Merge remote-tracking branch 'upstream/master' into cares_buildin

61 files changed, 2007 insertions, 403 deletions

diff --git a/src/core/lib/channel/channel_args.c b/src/core/lib/channel/channel_args.c
index 79ceeb66b3..3a56b1ff20 100644
--- a/src/core/lib/channel/channel_args.c
+++ b/src/core/lib/channel/channel_args.c
@@ -271,3 +271,21 @@ int grpc_channel_args_compare(const grpc_channel_args *a,
   }
   return 0;
 }
+
+int grpc_channel_arg_get_integer(grpc_arg *arg, grpc_integer_options options) {
+  if (arg->type != GRPC_ARG_INTEGER) {
+    gpr_log(GPR_ERROR, "%s ignored: it must be an integer", arg->key);
+    return options.default_value;
+  }
+  if (arg->value.integer < options.min_value) {
+    gpr_log(GPR_ERROR, "%s ignored: it must be >= %d", arg->key,
+            options.min_value);
+    return options.default_value;
+  }
+  if (arg->value.integer > options.max_value) {
+    gpr_log(GPR_ERROR, "%s ignored: it must be <= %d", arg->key,
+            options.max_value);
+    return options.default_value;
+  }
+  return arg->value.integer;
+}
diff --git a/src/core/lib/channel/channel_args.h b/src/core/lib/channel/channel_args.h
index aec61ee7c6..586a296d1f 100644
--- a/src/core/lib/channel/channel_args.h
+++ b/src/core/lib/channel/channel_args.h
@@ -89,4 +89,12 @@ uint32_t grpc_channel_args_compression_algorithm_get_states(
 int grpc_channel_args_compare(const grpc_channel_args *a,
                               const grpc_channel_args *b);
 
+typedef struct grpc_integer_options {
+  int default_value;  // Return this if value is outside of expected bounds.
+  int min_value;
+  int max_value;
+} grpc_integer_options;
+/** Returns the value of \a arg, subject to the contraints in \a options. */
+int grpc_channel_arg_get_integer(grpc_arg *arg, grpc_integer_options options);
+
 #endif /* GRPC_CORE_LIB_CHANNEL_CHANNEL_ARGS_H */
diff --git a/src/core/lib/channel/channel_stack.c b/src/core/lib/channel/channel_stack.c
index 98f304f2da..57d34d9e9a 100644
--- a/src/core/lib/channel/channel_stack.c
+++ b/src/core/lib/channel/channel_stack.c
@@ -32,6 +32,7 @@
  */
 
 #include "src/core/lib/channel/channel_stack.h"
+#include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 
 #include <stdlib.h>
@@ -157,13 +158,11 @@ void grpc_channel_stack_destroy(grpc_exec_ctx *exec_ctx,
   }
 }
 
-grpc_error *grpc_call_stack_init(grpc_exec_ctx *exec_ctx,
-                                 grpc_channel_stack *channel_stack,
-                                 int initial_refs, grpc_iomgr_cb_func destroy,
-                                 void *destroy_arg,
-                                 grpc_call_context_element *context,
-                                 const void *transport_server_data,
-                                 grpc_call_stack *call_stack) {
+grpc_error *grpc_call_stack_init(
+    grpc_exec_ctx *exec_ctx, grpc_channel_stack *channel_stack,
+    int initial_refs, grpc_iomgr_cb_func destroy, void *destroy_arg,
+    grpc_call_context_element *context, const void *transport_server_data,
+    gpr_timespec deadline, grpc_call_stack *call_stack) {
   grpc_channel_element *channel_elems = CHANNEL_ELEMS_FROM_STACK(channel_stack);
   grpc_call_element_args args;
   size_t count = channel_stack->count;
@@ -184,6 +183,7 @@ grpc_error *grpc_call_stack_init(grpc_exec_ctx *exec_ctx,
     args.call_stack = call_stack;
     args.server_transport_data = transport_server_data;
     args.context = context;
+    args.deadline = deadline;
     call_elems[i].filter = channel_elems[i].filter;
     call_elems[i].channel_data = channel_elems[i].channel_data;
     call_elems[i].call_data = user_data;
@@ -270,21 +270,38 @@ grpc_call_stack *grpc_call_stack_from_top_element(grpc_call_element *elem) {
       sizeof(grpc_call_stack)));
 }
 
+static void destroy_op(grpc_exec_ctx *exec_ctx, void *op, grpc_error *error) {
+  gpr_free(op);
+}
+
 void grpc_call_element_send_cancel(grpc_exec_ctx *exec_ctx,
-                                   grpc_call_element *cur_elem) {
-  grpc_transport_stream_op op;
-  memset(&op, 0, sizeof(op));
-  op.cancel_error = GRPC_ERROR_CANCELLED;
-  grpc_call_next_op(exec_ctx, cur_elem, &op);
+                                   grpc_call_element *elem) {
+  grpc_transport_stream_op *op = gpr_malloc(sizeof(*op));
+  memset(op, 0, sizeof(*op));
+  op->cancel_error = GRPC_ERROR_CANCELLED;
+  op->on_complete = grpc_closure_create(destroy_op, op);
+  elem->filter->start_transport_stream_op(exec_ctx, elem, op);
 }
 
 void grpc_call_element_send_cancel_with_message(grpc_exec_ctx *exec_ctx,
-                                                grpc_call_element *cur_elem,
+                                                grpc_call_element *elem,
                                                 grpc_status_code status,
                                                 gpr_slice *optional_message) {
-  grpc_transport_stream_op op;
-  memset(&op, 0, sizeof(op));
-  grpc_transport_stream_op_add_cancellation_with_message(&op, status,
+  grpc_transport_stream_op *op = gpr_malloc(sizeof(*op));
+  memset(op, 0, sizeof(*op));
+  op->on_complete = grpc_closure_create(destroy_op, op);
+  grpc_transport_stream_op_add_cancellation_with_message(op, status,
                                                          optional_message);
-  grpc_call_next_op(exec_ctx, cur_elem, &op);
+  elem->filter->start_transport_stream_op(exec_ctx, elem, op);
+}
+
+void grpc_call_element_send_close_with_message(grpc_exec_ctx *exec_ctx,
+                                               grpc_call_element *elem,
+                                               grpc_status_code status,
+                                               gpr_slice *optional_message) {
+  grpc_transport_stream_op *op = gpr_malloc(sizeof(*op));
+  memset(op, 0, sizeof(*op));
+  op->on_complete = grpc_closure_create(destroy_op, op);
+  grpc_transport_stream_op_add_close(op, status, optional_message);
+  elem->filter->start_transport_stream_op(exec_ctx, elem, op);
 }
diff --git a/src/core/lib/channel/channel_stack.h b/src/core/lib/channel/channel_stack.h
index 6b73cce380..1cfe2885d8 100644
--- a/src/core/lib/channel/channel_stack.h
+++ b/src/core/lib/channel/channel_stack.h
@@ -74,6 +74,7 @@ typedef struct {
   grpc_call_stack *call_stack;
   const void *server_transport_data;
   grpc_call_context_element *context;
+  gpr_timespec deadline;
 } grpc_call_element_args;
 
 typedef struct {
@@ -220,13 +221,11 @@ void grpc_channel_stack_destroy(grpc_exec_ctx *exec_ctx,
 /* Initialize a call stack given a channel stack. transport_server_data is
    expected to be NULL on a client, or an opaque transport owned pointer on the
    server. */
-grpc_error *grpc_call_stack_init(grpc_exec_ctx *exec_ctx,
-                                 grpc_channel_stack *channel_stack,
-                                 int initial_refs, grpc_iomgr_cb_func destroy,
-                                 void *destroy_arg,
-                                 grpc_call_context_element *context,
-                                 const void *transport_server_data,
-                                 grpc_call_stack *call_stack);
+grpc_error *grpc_call_stack_init(
+    grpc_exec_ctx *exec_ctx, grpc_channel_stack *channel_stack,
+    int initial_refs, grpc_iomgr_cb_func destroy, void *destroy_arg,
+    grpc_call_context_element *context, const void *transport_server_data,
+    gpr_timespec deadline, grpc_call_stack *call_stack);
 /* Set a pollset or a pollset_set for a call stack: must occur before the first
  * op is started */
 void grpc_call_stack_set_pollset_or_pollset_set(grpc_exec_ctx *exec_ctx,
@@ -290,6 +289,11 @@ void grpc_call_element_send_cancel_with_message(grpc_exec_ctx *exec_ctx,
                                                 grpc_status_code status,
                                                 gpr_slice *optional_message);
 
+void grpc_call_element_send_close_with_message(grpc_exec_ctx *exec_ctx,
+                                               grpc_call_element *cur_elem,
+                                               grpc_status_code status,
+                                               gpr_slice *optional_message);
+
 extern int grpc_trace_channel;
 
 #define GRPC_CALL_LOG_OP(sev, elem, op) \
diff --git a/src/core/lib/channel/compress_filter.c b/src/core/lib/channel/compress_filter.c
index 134180e619..0981d59f63 100644
--- a/src/core/lib/channel/compress_filter.c
+++ b/src/core/lib/channel/compress_filter.c
@@ -60,7 +60,7 @@ typedef struct call_data {
   /** If true, contents of \a compression_algorithm are authoritative */
   int has_compression_algorithm;
 
-  grpc_transport_stream_op send_op;
+  grpc_transport_stream_op *send_op;
   uint32_t send_length;
   uint32_t send_flags;
   gpr_slice incoming_slice;
@@ -199,11 +199,11 @@ static void finish_send_message(grpc_exec_ctx *exec_ctx,
 
   grpc_slice_buffer_stream_init(&calld->replacement_stream, &calld->slices,
                                 calld->send_flags);
-  calld->send_op.send_message = &calld->replacement_stream.base;
-  calld->post_send = calld->send_op.on_complete;
-  calld->send_op.on_complete = &calld->send_done;
+  calld->send_op->send_message = &calld->replacement_stream.base;
+  calld->post_send = calld->send_op->on_complete;
+  calld->send_op->on_complete = &calld->send_done;
 
-  grpc_call_next_op(exec_ctx, elem, &calld->send_op);
+  grpc_call_next_op(exec_ctx, elem, calld->send_op);
 }
 
 static void got_slice(grpc_exec_ctx *exec_ctx, void *elemp, grpc_error *error) {
@@ -220,7 +220,7 @@ static void got_slice(grpc_exec_ctx *exec_ctx, void *elemp, grpc_error *error) {
 static void continue_send_message(grpc_exec_ctx *exec_ctx,
                                   grpc_call_element *elem) {
   call_data *calld = elem->call_data;
-  while (grpc_byte_stream_next(exec_ctx, calld->send_op.send_message,
+  while (grpc_byte_stream_next(exec_ctx, calld->send_op->send_message,
                                &calld->incoming_slice, ~(size_t)0,
                                &calld->got_slice)) {
     gpr_slice_buffer_add(&calld->slices, calld->incoming_slice);
@@ -243,7 +243,7 @@ static void compress_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
   }
   if (op->send_message != NULL && !skip_compression(elem) &&
       0 == (op->send_message->flags & GRPC_WRITE_NO_COMPRESS)) {
-    calld->send_op = *op;
+    calld->send_op = op;
     calld->send_length = op->send_message->length;
     calld->send_flags = op->send_message->flags;
     continue_send_message(exec_ctx, elem);
diff --git a/src/core/lib/channel/deadline_filter.c b/src/core/lib/channel/deadline_filter.c
new file mode 100644
index 0000000000..079b98a2f8
--- /dev/null
+++ b/src/core/lib/channel/deadline_filter.c
@@ -0,0 +1,302 @@
+//
+// Copyright 2016, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+
+#include "src/core/lib/channel/deadline_filter.h"
+
+#include <stdbool.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/time.h>
+
+#include "src/core/lib/iomgr/exec_ctx.h"
+#include "src/core/lib/iomgr/timer.h"
+
+//
+// grpc_deadline_state
+//
+
+// Timer callback.
+static void timer_callback(grpc_exec_ctx* exec_ctx, void* arg,
+                           grpc_error* error) {
+  grpc_call_element* elem = arg;
+  grpc_deadline_state* deadline_state = elem->call_data;
+  gpr_mu_lock(&deadline_state->timer_mu);
+  deadline_state->timer_pending = false;
+  gpr_mu_unlock(&deadline_state->timer_mu);
+  if (error != GRPC_ERROR_CANCELLED) {
+    gpr_slice msg = gpr_slice_from_static_string("Deadline Exceeded");
+    grpc_call_element_send_cancel_with_message(
+        exec_ctx, elem, GRPC_STATUS_DEADLINE_EXCEEDED, &msg);
+    gpr_slice_unref(msg);
+  }
+  GRPC_CALL_STACK_UNREF(exec_ctx, deadline_state->call_stack, "deadline_timer");
+}
+
+// Starts the deadline timer.
+static void start_timer_if_needed(grpc_exec_ctx* exec_ctx,
+                                  grpc_call_element* elem,
+                                  gpr_timespec deadline) {
+  grpc_deadline_state* deadline_state = elem->call_data;
+  deadline = gpr_convert_clock_type(deadline, GPR_CLOCK_MONOTONIC);
+  if (gpr_time_cmp(deadline, gpr_inf_future(GPR_CLOCK_MONOTONIC)) != 0) {
+    // Take a reference to the call stack, to be owned by the timer.
+    GRPC_CALL_STACK_REF(deadline_state->call_stack, "deadline_timer");
+    gpr_mu_lock(&deadline_state->timer_mu);
+    deadline_state->timer_pending = true;
+    grpc_timer_init(exec_ctx, &deadline_state->timer, deadline, timer_callback,
+                    elem, gpr_now(GPR_CLOCK_MONOTONIC));
+    gpr_mu_unlock(&deadline_state->timer_mu);
+  }
+}
+
+// Cancels the deadline timer.
+static void cancel_timer_if_needed(grpc_exec_ctx* exec_ctx,
+                                   grpc_deadline_state* deadline_state) {
+  gpr_mu_lock(&deadline_state->timer_mu);
+  if (deadline_state->timer_pending) {
+    grpc_timer_cancel(exec_ctx, &deadline_state->timer);
+    deadline_state->timer_pending = false;
+  }
+  gpr_mu_unlock(&deadline_state->timer_mu);
+}
+
+// Callback run when the call is complete.
+static void on_complete(grpc_exec_ctx* exec_ctx, void* arg, grpc_error* error) {
+  grpc_deadline_state* deadline_state = arg;
+  cancel_timer_if_needed(exec_ctx, deadline_state);
+  // Invoke the next callback.
+  deadline_state->next_on_complete->cb(
+      exec_ctx, deadline_state->next_on_complete->cb_arg, error);
+}
+
+// Inject our own on_complete callback into op.
+static void inject_on_complete_cb(grpc_deadline_state* deadline_state,
+                                  grpc_transport_stream_op* op) {
+  deadline_state->next_on_complete = op->on_complete;
+  grpc_closure_init(&deadline_state->on_complete, on_complete, deadline_state);
+  op->on_complete = &deadline_state->on_complete;
+}
+
+// Callback and associated state for starting the timer after call stack
+// initialization has been completed.
+struct start_timer_after_init_state {
+  grpc_call_element* elem;
+  gpr_timespec deadline;
+  grpc_closure closure;
+};
+static void start_timer_after_init(grpc_exec_ctx* exec_ctx, void* arg,
+                                   grpc_error* error) {
+  struct start_timer_after_init_state* state = arg;
+  start_timer_if_needed(exec_ctx, state->elem, state->deadline);
+  gpr_free(state);
+}
+
+void grpc_deadline_state_init(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+                              grpc_call_element_args* args) {
+  grpc_deadline_state* deadline_state = elem->call_data;
+  memset(deadline_state, 0, sizeof(*deadline_state));
+  deadline_state->call_stack = args->call_stack;
+  gpr_mu_init(&deadline_state->timer_mu);
+  // Deadline will always be infinite on servers, so the timer will only be
+  // set on clients with a finite deadline.
+  const gpr_timespec deadline =
+      gpr_convert_clock_type(args->deadline, GPR_CLOCK_MONOTONIC);
+  if (gpr_time_cmp(deadline, gpr_inf_future(GPR_CLOCK_MONOTONIC)) != 0) {
+    // When the deadline passes, we indicate the failure by sending down
+    // an op with cancel_error set.  However, we can't send down any ops
+    // until after the call stack is fully initialized.  If we start the
+    // timer here, we have no guarantee that the timer won't pop before
+    // call stack initialization is finished.  To avoid that problem, we
+    // create a closure to start the timer, and we schedule that closure
+    // to be run after call stack initialization is done.
+    struct start_timer_after_init_state* state = gpr_malloc(sizeof(*state));
+    state->elem = elem;
+    state->deadline = deadline;
+    grpc_closure_init(&state->closure, start_timer_after_init, state);
+    grpc_exec_ctx_sched(exec_ctx, &state->closure, GRPC_ERROR_NONE, NULL);
+  }
+}
+
+void grpc_deadline_state_destroy(grpc_exec_ctx* exec_ctx,
+                                 grpc_call_element* elem) {
+  grpc_deadline_state* deadline_state = elem->call_data;
+  cancel_timer_if_needed(exec_ctx, deadline_state);
+  gpr_mu_destroy(&deadline_state->timer_mu);
+}
+
+void grpc_deadline_state_client_start_transport_stream_op(
+    grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+    grpc_transport_stream_op* op) {
+  grpc_deadline_state* deadline_state = elem->call_data;
+  if (op->cancel_error != GRPC_ERROR_NONE ||
+      op->close_error != GRPC_ERROR_NONE) {
+    cancel_timer_if_needed(exec_ctx, deadline_state);
+  } else {
+    // Make sure we know when the call is complete, so that we can cancel
+    // the timer.
+    if (op->recv_trailing_metadata != NULL) {
+      inject_on_complete_cb(deadline_state, op);
+    }
+  }
+}
+
+//
+// filter code
+//
+
+// Constructor for channel_data.  Used for both client and server filters.
+static void init_channel_elem(grpc_exec_ctx* exec_ctx,
+                              grpc_channel_element* elem,
+                              grpc_channel_element_args* args) {
+  GPR_ASSERT(!args->is_last);
+}
+
+// Destructor for channel_data.  Used for both client and server filters.
+static void destroy_channel_elem(grpc_exec_ctx* exec_ctx,
+                                 grpc_channel_element* elem) {}
+
+// Call data used for both client and server filter.
+typedef struct base_call_data {
+  grpc_deadline_state deadline_state;
+} base_call_data;
+
+// Additional call data used only for the server filter.
+typedef struct server_call_data {
+  base_call_data base;  // Must be first.
+  // The closure for receiving initial metadata.
+  grpc_closure recv_initial_metadata_ready;
+  // Received initial metadata batch.
+  grpc_metadata_batch* recv_initial_metadata;
+  // The original recv_initial_metadata_ready closure, which we chain to
+  // after our own closure is invoked.
+  grpc_closure* next_recv_initial_metadata_ready;
+} server_call_data;
+
+// Constructor for call_data.  Used for both client and server filters.
+static grpc_error* init_call_elem(grpc_exec_ctx* exec_ctx,
+                                  grpc_call_element* elem,
+                                  grpc_call_element_args* args) {
+  // Note: size of call data is different between client and server.
+  memset(elem->call_data, 0, elem->filter->sizeof_call_data);
+  grpc_deadline_state_init(exec_ctx, elem, args);
+  return GRPC_ERROR_NONE;
+}
+
+// Destructor for call_data.  Used for both client and server filters.
+static void destroy_call_elem(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+                              const grpc_call_final_info* final_info,
+                              void* and_free_memory) {
+  grpc_deadline_state_destroy(exec_ctx, elem);
+}
+
+// Method for starting a call op for client filter.
+static void client_start_transport_stream_op(grpc_exec_ctx* exec_ctx,
+                                             grpc_call_element* elem,
+                                             grpc_transport_stream_op* op) {
+  grpc_deadline_state_client_start_transport_stream_op(exec_ctx, elem, op);
+  // Chain to next filter.
+  grpc_call_next_op(exec_ctx, elem, op);
+}
+
+// Callback for receiving initial metadata on the server.
+static void recv_initial_metadata_ready(grpc_exec_ctx* exec_ctx, void* arg,
+                                        grpc_error* error) {
+  grpc_call_element* elem = arg;
+  server_call_data* calld = elem->call_data;
+  // Get deadline from metadata and start the timer if needed.
+  start_timer_if_needed(exec_ctx, elem, calld->recv_initial_metadata->deadline);
+  // Invoke the next callback.
+  calld->next_recv_initial_metadata_ready->cb(
+      exec_ctx, calld->next_recv_initial_metadata_ready->cb_arg, error);
+}
+
+// Method for starting a call op for server filter.
+static void server_start_transport_stream_op(grpc_exec_ctx* exec_ctx,
+                                             grpc_call_element* elem,
+                                             grpc_transport_stream_op* op) {
+  server_call_data* calld = elem->call_data;
+  if (op->cancel_error != GRPC_ERROR_NONE ||
+      op->close_error != GRPC_ERROR_NONE) {
+    cancel_timer_if_needed(exec_ctx, &calld->base.deadline_state);
+  } else {
+    // If we're receiving initial metadata, we need to get the deadline
+    // from the recv_initial_metadata_ready callback.  So we inject our
+    // own callback into that hook.
+    if (op->recv_initial_metadata_ready != NULL) {
+      calld->next_recv_initial_metadata_ready = op->recv_initial_metadata_ready;
+      calld->recv_initial_metadata = op->recv_initial_metadata;
+      grpc_closure_init(&calld->recv_initial_metadata_ready,
+                        recv_initial_metadata_ready, elem);
+      op->recv_initial_metadata_ready = &calld->recv_initial_metadata_ready;
+    }
+    // Make sure we know when the call is complete, so that we can cancel
+    // the timer.
+    // Note that we trigger this on recv_trailing_metadata, even though
+    // the client never sends trailing metadata, because this is the
+    // hook that tells us when the call is complete on the server side.
+    if (op->recv_trailing_metadata != NULL) {
+      inject_on_complete_cb(&calld->base.deadline_state, op);
+    }
+  }
+  // Chain to next filter.
+  grpc_call_next_op(exec_ctx, elem, op);
+}
+
+const grpc_channel_filter grpc_client_deadline_filter = {
+    client_start_transport_stream_op,
+    grpc_channel_next_op,
+    sizeof(base_call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset_or_pollset_set,
+    destroy_call_elem,
+    0,  // sizeof(channel_data)
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "deadline",
+};
+
+const grpc_channel_filter grpc_server_deadline_filter = {
+    server_start_transport_stream_op,
+    grpc_channel_next_op,
+    sizeof(server_call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset_or_pollset_set,
+    destroy_call_elem,
+    0,  // sizeof(channel_data)
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "deadline",
+};
diff --git a/src/core/lib/channel/deadline_filter.h b/src/core/lib/channel/deadline_filter.h
new file mode 100644
index 0000000000..685df87761
--- /dev/null
+++ b/src/core/lib/channel/deadline_filter.h
@@ -0,0 +1,79 @@
+//
+// Copyright 2016, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+
+#ifndef GRPC_CORE_LIB_CHANNEL_DEADLINE_FILTER_H
+#define GRPC_CORE_LIB_CHANNEL_DEADLINE_FILTER_H
+
+#include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/iomgr/timer.h"
+
+// State used for filters that enforce call deadlines.
+// Must be the first field in the filter's call_data.
+typedef struct grpc_deadline_state {
+  // We take a reference to the call stack for the timer callback.
+  grpc_call_stack* call_stack;
+  // Guards access to timer_pending and timer.
+  gpr_mu timer_mu;
+  // True if the timer callback is currently pending.
+  bool timer_pending;
+  // The deadline timer.
+  grpc_timer timer;
+  // Closure to invoke when the call is complete.
+  // We use this to cancel the timer.
+  grpc_closure on_complete;
+  // The original on_complete closure, which we chain to after our own
+  // closure is invoked.
+  grpc_closure* next_on_complete;
+} grpc_deadline_state;
+
+// To be used in a filter's init_call_elem(), destroy_call_elem(), and
+// start_transport_stream_op() methods to enforce call deadlines.
+//
+// REQUIRES: The first field in elem->call_data is a grpc_deadline_state.
+//
+// For grpc_deadline_state_client_start_transport_stream_op(), it is the
+// caller's responsibility to chain to the next filter if necessary
+// after the function returns.
+void grpc_deadline_state_init(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+                              grpc_call_element_args* args);
+void grpc_deadline_state_destroy(grpc_exec_ctx* exec_ctx,
+                                 grpc_call_element* elem);
+void grpc_deadline_state_client_start_transport_stream_op(
+    grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+    grpc_transport_stream_op* op);
+
+// Deadline filters for direct client channels and server channels.
+// Note: Deadlines for non-direct client channels are handled by the
+// client_channel filter.
+extern const grpc_channel_filter grpc_client_deadline_filter;
+extern const grpc_channel_filter grpc_server_deadline_filter;
+
+#endif /* GRPC_CORE_LIB_CHANNEL_DEADLINE_FILTER_H */
diff --git a/src/core/lib/channel/handshaker.c b/src/core/lib/channel/handshaker.c
index c0979f5e80..8f9fb17a31 100644
--- a/src/core/lib/channel/handshaker.c
+++ b/src/core/lib/channel/handshaker.c
@@ -33,8 +33,8 @@
 
 #include <string.h>
 
-#include <grpc/impl/codegen/alloc.h>
-#include <grpc/impl/codegen/log.h>
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
 
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/handshaker.h"
diff --git a/src/core/lib/channel/handshaker.h b/src/core/lib/channel/handshaker.h
index b276f6028c..d574b46242 100644
--- a/src/core/lib/channel/handshaker.h
+++ b/src/core/lib/channel/handshaker.h
@@ -35,8 +35,6 @@
 #define GRPC_CORE_LIB_CHANNEL_HANDSHAKER_H
 
 #include <grpc/impl/codegen/grpc_types.h>
-#include <grpc/impl/codegen/time.h>
-#include <grpc/support/slice_buffer.h>
 
 #include "src/core/lib/iomgr/closure.h"
 #include "src/core/lib/iomgr/endpoint.h"
diff --git a/src/core/lib/channel/http_client_filter.c b/src/core/lib/channel/http_client_filter.c
index ef68cc86ea..1dc05fb20d 100644
--- a/src/core/lib/channel/http_client_filter.c
+++ b/src/core/lib/channel/http_client_filter.c
@@ -103,8 +103,8 @@ static grpc_mdelem *client_recv_filter(void *user_data, grpc_mdelem *md) {
                  grpc_mdstr_as_c_string(md->value));
     gpr_slice message = gpr_slice_from_copied_string(message_string);
     gpr_free(message_string);
-    grpc_call_element_send_cancel_with_message(a->exec_ctx, a->elem,
-                                               GRPC_STATUS_CANCELLED, &message);
+    grpc_call_element_send_close_with_message(a->exec_ctx, a->elem,
+                                              GRPC_STATUS_CANCELLED, &message);
     return NULL;
   } else if (md == GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC) {
     return NULL;
@@ -233,7 +233,6 @@ static void hc_mutate_op(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
     if (method == GRPC_MDELEM_METHOD_GET) {
       /* allocate memory to hold the entire payload */
       calld->payload_bytes = gpr_malloc(op->send_message->length);
-      GPR_ASSERT(calld->payload_bytes);
 
       /* read slices of send_message and copy into payload_bytes */
       calld->send_op = *op;
diff --git a/src/core/lib/channel/message_size_filter.c b/src/core/lib/channel/message_size_filter.c
new file mode 100644
index 0000000000..02fc68fc3a
--- /dev/null
+++ b/src/core/lib/channel/message_size_filter.c
@@ -0,0 +1,169 @@
+//
+// Copyright 2016, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+
+#include "src/core/lib/channel/message_size_filter.h"
+
+#include <limits.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
+
+#include "src/core/lib/channel/channel_args.h"
+
+#define DEFAULT_MAX_SEND_MESSAGE_LENGTH -1  // Unlimited.
+// The protobuf library will (by default) start warning at 100 megs.
+#define DEFAULT_MAX_RECV_MESSAGE_LENGTH (4 * 1024 * 1024)
+
+typedef struct call_data {
+  // Receive closures are chained: we inject this closure as the
+  // recv_message_ready up-call on transport_stream_op, and remember to
+  // call our next_recv_message_ready member after handling it.
+  grpc_closure recv_message_ready;
+  // Used by recv_message_ready.
+  grpc_byte_stream** recv_message;
+  // Original recv_message_ready callback, invoked after our own.
+  grpc_closure* next_recv_message_ready;
+} call_data;
+
+typedef struct channel_data {
+  int max_send_size;
+  int max_recv_size;
+} channel_data;
+
+// Callback invoked when we receive a message.  Here we check the max
+// receive message size.
+static void recv_message_ready(grpc_exec_ctx* exec_ctx, void* user_data,
+                               grpc_error* error) {
+  grpc_call_element* elem = user_data;
+  call_data* calld = elem->call_data;
+  channel_data* chand = elem->channel_data;
+  if (*calld->recv_message != NULL && chand->max_recv_size >= 0 &&
+      (*calld->recv_message)->length > (size_t)chand->max_recv_size) {
+    char* message_string;
+    gpr_asprintf(&message_string,
+                 "Received message larger than max (%u vs. %d)",
+                 (*calld->recv_message)->length, chand->max_recv_size);
+    gpr_slice message = gpr_slice_from_copied_string(message_string);
+    gpr_free(message_string);
+    grpc_call_element_send_close_with_message(
+        exec_ctx, elem, GRPC_STATUS_INVALID_ARGUMENT, &message);
+  }
+  // Invoke the next callback.
+  grpc_exec_ctx_sched(exec_ctx, calld->next_recv_message_ready, error, NULL);
+}
+
+// Start transport op.
+static void start_transport_stream_op(grpc_exec_ctx* exec_ctx,
+                                      grpc_call_element* elem,
+                                      grpc_transport_stream_op* op) {
+  call_data* calld = elem->call_data;
+  channel_data* chand = elem->channel_data;
+  // Check max send message size.
+  if (op->send_message != NULL && chand->max_send_size >= 0 &&
+      op->send_message->length > (size_t)chand->max_send_size) {
+    char* message_string;
+    gpr_asprintf(&message_string, "Sent message larger than max (%u vs. %d)",
+                 op->send_message->length, chand->max_send_size);
+    gpr_slice message = gpr_slice_from_copied_string(message_string);
+    gpr_free(message_string);
+    grpc_call_element_send_close_with_message(
+        exec_ctx, elem, GRPC_STATUS_INVALID_ARGUMENT, &message);
+  }
+  // Inject callback for receiving a message.
+  if (op->recv_message_ready != NULL) {
+    calld->next_recv_message_ready = op->recv_message_ready;
+    calld->recv_message = op->recv_message;
+    op->recv_message_ready = &calld->recv_message_ready;
+  }
+  // Chain to the next filter.
+  grpc_call_next_op(exec_ctx, elem, op);
+}
+
+// Constructor for call_data.
+static grpc_error* init_call_elem(grpc_exec_ctx* exec_ctx,
+                                  grpc_call_element* elem,
+                                  grpc_call_element_args* args) {
+  call_data* calld = elem->call_data;
+  calld->next_recv_message_ready = NULL;
+  grpc_closure_init(&calld->recv_message_ready, recv_message_ready, elem);
+  return GRPC_ERROR_NONE;
+}
+
+// Destructor for call_data.
+static void destroy_call_elem(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
+                              const grpc_call_final_info* final_info,
+                              void* ignored) {}
+
+// Constructor for channel_data.
+static void init_channel_elem(grpc_exec_ctx* exec_ctx,
+                              grpc_channel_element* elem,
+                              grpc_channel_element_args* args) {
+  GPR_ASSERT(!args->is_last);
+  channel_data* chand = elem->channel_data;
+  memset(chand, 0, sizeof(*chand));
+  chand->max_send_size = DEFAULT_MAX_SEND_MESSAGE_LENGTH;
+  chand->max_recv_size = DEFAULT_MAX_RECV_MESSAGE_LENGTH;
+  for (size_t i = 0; i < args->channel_args->num_args; ++i) {
+    if (strcmp(args->channel_args->args[i].key,
+               GRPC_ARG_MAX_SEND_MESSAGE_LENGTH) == 0) {
+      const grpc_integer_options options = {DEFAULT_MAX_SEND_MESSAGE_LENGTH, 0,
+                                            INT_MAX};
+      chand->max_send_size =
+          grpc_channel_arg_get_integer(&args->channel_args->args[i], options);
+    }
+    if (strcmp(args->channel_args->args[i].key,
+               GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH) == 0) {
+      const grpc_integer_options options = {DEFAULT_MAX_RECV_MESSAGE_LENGTH, 0,
+                                            INT_MAX};
+      chand->max_recv_size =
+          grpc_channel_arg_get_integer(&args->channel_args->args[i], options);
+    }
+  }
+}
+
+// Destructor for channel_data.
+static void destroy_channel_elem(grpc_exec_ctx* exec_ctx,
+                                 grpc_channel_element* elem) {}
+
+const grpc_channel_filter grpc_message_size_filter = {
+    start_transport_stream_op,
+    grpc_channel_next_op,
+    sizeof(call_data),
+    init_call_elem,
+    grpc_call_stack_ignore_set_pollset_or_pollset_set,
+    destroy_call_elem,
+    sizeof(channel_data),
+    init_channel_elem,
+    destroy_channel_elem,
+    grpc_call_next_get_peer,
+    "message_size"};
diff --git a/src/core/lib/channel/message_size_filter.h b/src/core/lib/channel/message_size_filter.h
new file mode 100644
index 0000000000..a88ff7f81a
--- /dev/null
+++ b/src/core/lib/channel/message_size_filter.h
@@ -0,0 +1,39 @@
+//
+// Copyright 2016, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+
+#ifndef GRPC_CORE_LIB_CHANNEL_MESSAGE_SIZE_FILTER_H
+#define GRPC_CORE_LIB_CHANNEL_MESSAGE_SIZE_FILTER_H
+
+#include "src/core/lib/channel/channel_stack.h"
+
+extern const grpc_channel_filter grpc_message_size_filter;
+
+#endif /* GRPC_CORE_LIB_CHANNEL_MESSAGE_SIZE_FILTER_H */
diff --git a/src/core/lib/http/format_request.c b/src/core/lib/http/format_request.c
index 9240356fea..e818b70113 100644
--- a/src/core/lib/http/format_request.c
+++ b/src/core/lib/http/format_request.c
@@ -44,7 +44,7 @@
 #include "src/core/lib/support/string.h"
 
 static void fill_common_header(const grpc_httpcli_request *request,
-                               gpr_strvec *buf) {
+                               gpr_strvec *buf, bool connection_close) {
   size_t i;
   gpr_strvec_add(buf, gpr_strdup(request->http.path));
   gpr_strvec_add(buf, gpr_strdup(" HTTP/1.0\r\n"));
@@ -52,7 +52,8 @@ static void fill_common_header(const grpc_httpcli_request *request,
   gpr_strvec_add(buf, gpr_strdup("Host: "));
   gpr_strvec_add(buf, gpr_strdup(request->host));
   gpr_strvec_add(buf, gpr_strdup("\r\n"));
-  gpr_strvec_add(buf, gpr_strdup("Connection: close\r\n"));
+  if (connection_close)
+    gpr_strvec_add(buf, gpr_strdup("Connection: close\r\n"));
   gpr_strvec_add(buf,
                  gpr_strdup("User-Agent: " GRPC_HTTPCLI_USER_AGENT "\r\n"));
   /* user supplied headers */
@@ -71,7 +72,7 @@ gpr_slice grpc_httpcli_format_get_request(const grpc_httpcli_request *request) {
 
   gpr_strvec_init(&out);
   gpr_strvec_add(&out, gpr_strdup("GET "));
-  fill_common_header(request, &out);
+  fill_common_header(request, &out, true);
   gpr_strvec_add(&out, gpr_strdup("\r\n"));
 
   flat = gpr_strvec_flatten(&out, &flat_len);
@@ -91,7 +92,7 @@ gpr_slice grpc_httpcli_format_post_request(const grpc_httpcli_request *request,
   gpr_strvec_init(&out);
 
   gpr_strvec_add(&out, gpr_strdup("POST "));
-  fill_common_header(request, &out);
+  fill_common_header(request, &out, true);
   if (body_bytes) {
     uint8_t has_content_type = 0;
     for (i = 0; i < request->http.hdr_count; i++) {
@@ -118,3 +119,16 @@ gpr_slice grpc_httpcli_format_post_request(const grpc_httpcli_request *request,
 
   return gpr_slice_new(tmp, out_len, gpr_free);
 }
+
+gpr_slice grpc_httpcli_format_connect_request(
+    const grpc_httpcli_request *request) {
+  gpr_strvec out;
+  gpr_strvec_init(&out);
+  gpr_strvec_add(&out, gpr_strdup("CONNECT "));
+  fill_common_header(request, &out, false);
+  gpr_strvec_add(&out, gpr_strdup("\r\n"));
+  size_t flat_len;
+  char *flat = gpr_strvec_flatten(&out, &flat_len);
+  gpr_strvec_destroy(&out);
+  return gpr_slice_new(flat, flat_len, gpr_free);
+}
diff --git a/src/core/lib/http/format_request.h b/src/core/lib/http/format_request.h
index 1543efe4b0..7abd55f2f7 100644
--- a/src/core/lib/http/format_request.h
+++ b/src/core/lib/http/format_request.h
@@ -41,5 +41,7 @@ gpr_slice grpc_httpcli_format_get_request(const grpc_httpcli_request *request);
 gpr_slice grpc_httpcli_format_post_request(const grpc_httpcli_request *request,
                                            const char *body_bytes,
                                            size_t body_size);
+gpr_slice grpc_httpcli_format_connect_request(
+    const grpc_httpcli_request *request);
 
 #endif /* GRPC_CORE_LIB_HTTP_FORMAT_REQUEST_H */
diff --git a/src/core/lib/http/httpcli.c b/src/core/lib/http/httpcli.c
index 18135bcb58..7f3c2d120d 100644
--- a/src/core/lib/http/httpcli.c
+++ b/src/core/lib/http/httpcli.c
@@ -146,7 +146,7 @@ static void on_read(grpc_exec_ctx *exec_ctx, void *user_data,
     if (GPR_SLICE_LENGTH(req->incoming.slices[i])) {
       req->have_read_byte = 1;
       grpc_error *err =
-          grpc_http_parser_parse(&req->parser, req->incoming.slices[i]);
+          grpc_http_parser_parse(&req->parser, req->incoming.slices[i], NULL);
       if (err != GRPC_ERROR_NONE) {
         finish(exec_ctx, req, err);
         return;
diff --git a/src/core/lib/http/httpcli.h b/src/core/lib/http/httpcli.h
index 662e176f4c..320c0f86c6 100644
--- a/src/core/lib/http/httpcli.h
+++ b/src/core/lib/http/httpcli.h
@@ -93,8 +93,7 @@ void grpc_httpcli_context_destroy(grpc_httpcli_context *context);
    'request' contains request parameters - these are caller owned and can be
      destroyed once the call returns
    'deadline' contains a deadline for the request (or gpr_inf_future)
-   'on_response' is a callback to report results to (and 'user_data' is a user
-     supplied pointer to pass to said call) */
+   'on_response' is a callback to report results to */
 void grpc_httpcli_get(grpc_exec_ctx *exec_ctx, grpc_httpcli_context *context,
                       grpc_polling_entity *pollent,
                       const grpc_httpcli_request *request,
@@ -113,8 +112,7 @@ void grpc_httpcli_get(grpc_exec_ctx *exec_ctx, grpc_httpcli_context *context,
    'deadline' contains a deadline for the request (or gpr_inf_future)
    'em' points to a caller owned event manager that must be alive for the
      lifetime of the request
-   'on_response' is a callback to report results to (and 'user_data' is a user
-     supplied pointer to pass to said call)
+   'on_response' is a callback to report results to
    Does not support ?var1=val1&var2=val2 in the path. */
 void grpc_httpcli_post(grpc_exec_ctx *exec_ctx, grpc_httpcli_context *context,
                        grpc_polling_entity *pollent,
diff --git a/src/core/lib/http/parser.c b/src/core/lib/http/parser.c
index 92ed08ae51..be9e9b6b63 100644
--- a/src/core/lib/http/parser.c
+++ b/src/core/lib/http/parser.c
@@ -33,6 +33,7 @@
 
 #include "src/core/lib/http/parser.h"
 
+#include <stdbool.h>
 #include <string.h>
 
 #include <grpc/support/alloc.h>
@@ -200,7 +201,8 @@ done:
   return error;
 }
 
-static grpc_error *finish_line(grpc_http_parser *parser) {
+static grpc_error *finish_line(grpc_http_parser *parser,
+                               bool *found_body_start) {
   grpc_error *err;
   switch (parser->state) {
     case GRPC_HTTP_FIRST_LINE:
@@ -211,6 +213,7 @@ static grpc_error *finish_line(grpc_http_parser *parser) {
     case GRPC_HTTP_HEADERS:
       if (parser->cur_line_length == parser->cur_line_end_length) {
         parser->state = GRPC_HTTP_BODY;
+        *found_body_start = true;
         break;
       }
       err = add_header(parser);
@@ -274,7 +277,8 @@ static bool check_line(grpc_http_parser *parser) {
   return false;
 }
 
-static grpc_error *addbyte(grpc_http_parser *parser, uint8_t byte) {
+static grpc_error *addbyte(grpc_http_parser *parser, uint8_t byte,
+                           bool *found_body_start) {
   switch (parser->state) {
     case GRPC_HTTP_FIRST_LINE:
     case GRPC_HTTP_HEADERS:
@@ -282,20 +286,18 @@ static grpc_error *addbyte(grpc_http_parser *parser, uint8_t byte) {
         if (grpc_http1_trace)
           gpr_log(GPR_ERROR, "HTTP client max line length (%d) exceeded",
                   GRPC_HTTP_PARSER_MAX_HEADER_LENGTH);
-        return 0;
+        return GRPC_ERROR_NONE;
       }
       parser->cur_line[parser->cur_line_length] = byte;
       parser->cur_line_length++;
       if (check_line(parser)) {
-        return finish_line(parser);
-      } else {
-        return GRPC_ERROR_NONE;
+        return finish_line(parser, found_body_start);
       }
-      GPR_UNREACHABLE_CODE(return 0);
+      return GRPC_ERROR_NONE;
     case GRPC_HTTP_BODY:
       return addbyte_body(parser, byte);
   }
-  GPR_UNREACHABLE_CODE(return 0);
+  GPR_UNREACHABLE_CODE(return GRPC_ERROR_NONE);
 }
 
 void grpc_http_parser_init(grpc_http_parser *parser, grpc_http_type type,
@@ -331,14 +333,15 @@ void grpc_http_response_destroy(grpc_http_response *response) {
   gpr_free(response->hdrs);
 }
 
-grpc_error *grpc_http_parser_parse(grpc_http_parser *parser, gpr_slice slice) {
-  size_t i;
-
-  for (i = 0; i < GPR_SLICE_LENGTH(slice); i++) {
-    grpc_error *err = addbyte(parser, GPR_SLICE_START_PTR(slice)[i]);
+grpc_error *grpc_http_parser_parse(grpc_http_parser *parser, gpr_slice slice,
+                                   size_t *start_of_body) {
+  for (size_t i = 0; i < GPR_SLICE_LENGTH(slice); i++) {
+    bool found_body_start = false;
+    grpc_error *err =
+        addbyte(parser, GPR_SLICE_START_PTR(slice)[i], &found_body_start);
     if (err != GRPC_ERROR_NONE) return err;
+    if (found_body_start && start_of_body != NULL) *start_of_body = i + 1;
   }
-
   return GRPC_ERROR_NONE;
 }
 
diff --git a/src/core/lib/http/parser.h b/src/core/lib/http/parser.h
index 6df3cc8b13..fab42979cd 100644
--- a/src/core/lib/http/parser.h
+++ b/src/core/lib/http/parser.h
@@ -113,7 +113,9 @@ void grpc_http_parser_init(grpc_http_parser *parser, grpc_http_type type,
                            void *request_or_response);
 void grpc_http_parser_destroy(grpc_http_parser *parser);
 
-grpc_error *grpc_http_parser_parse(grpc_http_parser *parser, gpr_slice slice);
+/* Sets \a start_of_body to the offset in \a slice of the start of the body. */
+grpc_error *grpc_http_parser_parse(grpc_http_parser *parser, gpr_slice slice,
+                                   size_t *start_of_body);
 grpc_error *grpc_http_parser_eof(grpc_http_parser *parser);
 
 void grpc_http_request_destroy(grpc_http_request *request);
diff --git a/src/core/lib/iomgr/closure.c b/src/core/lib/iomgr/closure.c
index 0b6c3b2539..1ba0a5c141 100644
--- a/src/core/lib/iomgr/closure.c
+++ b/src/core/lib/iomgr/closure.c
@@ -41,6 +41,10 @@ void grpc_closure_init(grpc_closure *closure, grpc_iomgr_cb_func cb,
   closure->cb_arg = cb_arg;
 }
 
+void grpc_closure_list_init(grpc_closure_list *closure_list) {
+  closure_list->head = closure_list->tail = NULL;
+}
+
 void grpc_closure_list_append(grpc_closure_list *closure_list,
                               grpc_closure *closure, grpc_error *error) {
   if (closure == NULL) {
diff --git a/src/core/lib/iomgr/closure.h b/src/core/lib/iomgr/closure.h
index 08e59a168e..c1a22b6021 100644
--- a/src/core/lib/iomgr/closure.h
+++ b/src/core/lib/iomgr/closure.h
@@ -37,6 +37,7 @@
 #include <grpc/support/port_platform.h>
 #include <stdbool.h>
 #include "src/core/lib/iomgr/error.h"
+#include "src/core/lib/support/mpscq.h"
 
 struct grpc_closure;
 typedef struct grpc_closure grpc_closure;
@@ -60,6 +61,14 @@ typedef void (*grpc_iomgr_cb_func)(grpc_exec_ctx *exec_ctx, void *arg,
 
 /** A closure over a grpc_iomgr_cb_func. */
 struct grpc_closure {
+  /** Once queued, next indicates the next queued closure; before then, scratch
+   *  space */
+  union {
+    grpc_closure *next;
+    gpr_mpscq_node atm_next;
+    uintptr_t scratch;
+  } next_data;
+
   /** Bound callback. */
   grpc_iomgr_cb_func cb;
 
@@ -68,13 +77,6 @@ struct grpc_closure {
 
   /** Once queued, the result of the closure. Before then: scratch space */
   grpc_error *error;
-
-  /** Once queued, next indicates the next queued closure; before then, scratch
-   *  space */
-  union {
-    grpc_closure *next;
-    uintptr_t scratch;
-  } next_data;
 };
 
 /** Initializes \a closure with \a cb and \a cb_arg. */
@@ -87,6 +89,8 @@ grpc_closure *grpc_closure_create(grpc_iomgr_cb_func cb, void *cb_arg);
 #define GRPC_CLOSURE_LIST_INIT \
   { NULL, NULL }
 
+void grpc_closure_list_init(grpc_closure_list *list);
+
 /** add \a closure to the end of \a list
     and set \a closure's result to \a error */
 void grpc_closure_list_append(grpc_closure_list *list, grpc_closure *closure,
diff --git a/src/core/lib/iomgr/combiner.c b/src/core/lib/iomgr/combiner.c
new file mode 100644
index 0000000000..831bdb4aff
--- /dev/null
+++ b/src/core/lib/iomgr/combiner.c
@@ -0,0 +1,293 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/iomgr/combiner.h"
+
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+
+#include "src/core/lib/iomgr/workqueue.h"
+#include "src/core/lib/profiling/timers.h"
+
+int grpc_combiner_trace = 0;
+
+#define GRPC_COMBINER_TRACE(fn) \
+  do {                          \
+    if (grpc_combiner_trace) {  \
+      fn;                       \
+    }                           \
+  } while (0)
+
+struct grpc_combiner {
+  grpc_workqueue *optional_workqueue;
+  gpr_mpscq queue;
+  // state is:
+  // lower bit - zero if orphaned
+  // other bits - number of items queued on the lock
+  gpr_atm state;
+  bool take_async_break_before_final_list;
+  grpc_closure_list final_list;
+  grpc_closure continue_finishing;
+};
+
+grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue) {
+  grpc_combiner *lock = gpr_malloc(sizeof(*lock));
+  lock->optional_workqueue = optional_workqueue;
+  gpr_atm_no_barrier_store(&lock->state, 1);
+  gpr_mpscq_init(&lock->queue);
+  lock->take_async_break_before_final_list = false;
+  grpc_closure_list_init(&lock->final_list);
+  GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p create", lock));
+  return lock;
+}
+
+static void really_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG, "C:%p really_destroy", lock));
+  GPR_ASSERT(gpr_atm_no_barrier_load(&lock->state) == 0);
+  gpr_mpscq_destroy(&lock->queue);
+  GRPC_WORKQUEUE_UNREF(exec_ctx, lock->optional_workqueue, "combiner");
+  gpr_free(lock);
+}
+
+void grpc_combiner_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  gpr_atm old_state = gpr_atm_full_fetch_add(&lock->state, -1);
+  GRPC_COMBINER_TRACE(gpr_log(
+      GPR_DEBUG, "C:%p really_destroy old_state=%" PRIdPTR, lock, old_state));
+  if (old_state == 1) {
+    really_destroy(exec_ctx, lock);
+  }
+}
+
+static bool maybe_finish_one(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+static void finish(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+
+static void continue_finishing_mainline(grpc_exec_ctx *exec_ctx, void *arg,
+                                        grpc_error *error) {
+  GPR_TIMER_BEGIN("combiner.continue_executing_mainline", 0);
+  grpc_combiner *lock = arg;
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p continue_finishing_mainline", lock));
+  GPR_ASSERT(exec_ctx->active_combiner == NULL);
+  exec_ctx->active_combiner = lock;
+  if (maybe_finish_one(exec_ctx, lock)) finish(exec_ctx, lock);
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  exec_ctx->active_combiner = NULL;
+  GPR_TIMER_END("combiner.continue_executing_mainline", 0);
+}
+
+static void execute_final(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.execute_final", 0);
+  grpc_closure *c = lock->final_list.head;
+  GPR_ASSERT(c != NULL);
+  grpc_closure_list_init(&lock->final_list);
+  lock->take_async_break_before_final_list = false;
+  int loops = 0;
+  while (c != NULL) {
+    GRPC_COMBINER_TRACE(
+        gpr_log(GPR_DEBUG, "C:%p execute_final[%d] c=%p", lock, loops, c));
+    grpc_closure *next = c->next_data.next;
+    grpc_error *error = c->error;
+    c->cb(exec_ctx, c->cb_arg, error);
+    GRPC_ERROR_UNREF(error);
+    c = next;
+    loops++;
+  }
+  GPR_TIMER_END("combiner.execute_final", 0);
+}
+
+static void continue_executing_final(grpc_exec_ctx *exec_ctx, void *arg,
+                                     grpc_error *error) {
+  GPR_TIMER_BEGIN("combiner.continue_executing_final", 0);
+  grpc_combiner *lock = arg;
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p continue_executing_final", lock));
+  GPR_ASSERT(exec_ctx->active_combiner == NULL);
+  exec_ctx->active_combiner = lock;
+  // quick peek to see if new things have turned up on the queue: if so, go back
+  // to executing them before the final list
+  if ((gpr_atm_acq_load(&lock->state) >> 1) > 1) {
+    if (maybe_finish_one(exec_ctx, lock)) finish(exec_ctx, lock);
+  } else {
+    execute_final(exec_ctx, lock);
+    finish(exec_ctx, lock);
+  }
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  exec_ctx->active_combiner = NULL;
+  GPR_TIMER_END("combiner.continue_executing_final", 0);
+}
+
+static bool start_execute_final(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.start_execute_final", 0);
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG,
+              "C:%p start_execute_final take_async_break_before_final_list=%d",
+              lock, lock->take_async_break_before_final_list));
+  if (lock->take_async_break_before_final_list) {
+    grpc_closure_init(&lock->continue_finishing, continue_executing_final,
+                      lock);
+    grpc_exec_ctx_sched(exec_ctx, &lock->continue_finishing, GRPC_ERROR_NONE,
+                        GRPC_WORKQUEUE_REF(lock->optional_workqueue, "sched"));
+    GPR_TIMER_END("combiner.start_execute_final", 0);
+    return false;
+  } else {
+    execute_final(exec_ctx, lock);
+    GPR_TIMER_END("combiner.start_execute_final", 0);
+    return true;
+  }
+}
+
+static bool maybe_finish_one(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  GPR_TIMER_BEGIN("combiner.maybe_finish_one", 0);
+  gpr_mpscq_node *n = gpr_mpscq_pop(&lock->queue);
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p maybe_finish_one n=%p", lock, n));
+  GPR_ASSERT(exec_ctx->active_combiner == lock);
+  if (n == NULL) {
+    // Queue is in an transiently inconsistent state: a new item is being queued
+    // but is not visible to this thread yet.
+    // Use this as a cue that we should go off and do something else for a while
+    // (and come back later)
+    grpc_closure_init(&lock->continue_finishing, continue_finishing_mainline,
+                      lock);
+    grpc_exec_ctx_sched(exec_ctx, &lock->continue_finishing, GRPC_ERROR_NONE,
+                        GRPC_WORKQUEUE_REF(lock->optional_workqueue, "sched"));
+    GPR_TIMER_END("combiner.maybe_finish_one", 0);
+    return false;
+  }
+  grpc_closure *cl = (grpc_closure *)n;
+  grpc_error *error = cl->error;
+  cl->cb(exec_ctx, cl->cb_arg, error);
+  GRPC_ERROR_UNREF(error);
+  GPR_TIMER_END("combiner.maybe_finish_one", 0);
+  return true;
+}
+
+static void finish(grpc_exec_ctx *exec_ctx, grpc_combiner *lock) {
+  bool (*executor)(grpc_exec_ctx * exec_ctx, grpc_combiner * lock);
+  GPR_TIMER_BEGIN("combiner.finish", 0);
+  int loops = 0;
+  do {
+    executor = maybe_finish_one;
+    gpr_atm old_state = gpr_atm_full_fetch_add(&lock->state, -2);
+    GRPC_COMBINER_TRACE(gpr_log(GPR_DEBUG,
+                                "C:%p finish[%d] old_state=%" PRIdPTR, lock,
+                                loops, old_state));
+    switch (old_state) {
+      default:
+        // we have multiple queued work items: just continue executing them
+        break;
+      case 5:  // we're down to one queued item: if it's the final list we
+      case 4:  // should do that
+        if (!grpc_closure_list_empty(lock->final_list)) {
+          executor = start_execute_final;
+        }
+        break;
+      case 3:  // had one count, one unorphaned --> unlocked unorphaned
+        GPR_TIMER_END("combiner.finish", 0);
+        return;
+      case 2:  // and one count, one orphaned --> unlocked and orphaned
+        really_destroy(exec_ctx, lock);
+        GPR_TIMER_END("combiner.finish", 0);
+        return;
+      case 1:
+      case 0:
+        // these values are illegal - representing an already unlocked or
+        // deleted lock
+        GPR_UNREACHABLE_CODE(return );
+    }
+    loops++;
+  } while (executor(exec_ctx, lock));
+  GPR_TIMER_END("combiner.finish", 0);
+}
+
+void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                           grpc_closure *cl, grpc_error *error) {
+  GRPC_COMBINER_TRACE(
+      gpr_log(GPR_DEBUG, "C:%p grpc_combiner_execute c=%p", lock, cl));
+  GPR_TIMER_BEGIN("combiner.execute", 0);
+  gpr_atm last = gpr_atm_full_fetch_add(&lock->state, 2);
+  GPR_ASSERT(last & 1);  // ensure lock has not been destroyed
+  if (last == 1) {
+    exec_ctx->active_combiner = lock;
+    GPR_TIMER_BEGIN("combiner.execute_first_cb", 0);
+    cl->cb(exec_ctx, cl->cb_arg, error);
+    GPR_TIMER_END("combiner.execute_first_cb", 0);
+    GRPC_ERROR_UNREF(error);
+    finish(exec_ctx, lock);
+    GPR_ASSERT(exec_ctx->active_combiner == lock);
+    exec_ctx->active_combiner = NULL;
+  } else {
+    cl->error = error;
+    gpr_mpscq_push(&lock->queue, &cl->next_data.atm_next);
+  }
+  GPR_TIMER_END("combiner.execute", 0);
+}
+
+static void enqueue_finally(grpc_exec_ctx *exec_ctx, void *closure,
+                            grpc_error *error) {
+  grpc_combiner_execute_finally(exec_ctx, exec_ctx->active_combiner, closure,
+                                GRPC_ERROR_REF(error), false);
+}
+
+void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                                   grpc_closure *closure, grpc_error *error,
+                                   bool force_async_break) {
+  GRPC_COMBINER_TRACE(gpr_log(
+      GPR_DEBUG,
+      "C:%p grpc_combiner_execute_finally c=%p force_async_break=%d; ac=%p",
+      lock, closure, force_async_break, exec_ctx->active_combiner));
+  GPR_TIMER_BEGIN("combiner.execute_finally", 0);
+  if (exec_ctx->active_combiner != lock) {
+    GPR_TIMER_MARK("slowpath", 0);
+    grpc_combiner_execute(exec_ctx, lock,
+                          grpc_closure_create(enqueue_finally, closure), error);
+    GPR_TIMER_END("combiner.execute_finally", 0);
+    return;
+  }
+
+  if (force_async_break) {
+    lock->take_async_break_before_final_list = true;
+  }
+  if (grpc_closure_list_empty(lock->final_list)) {
+    gpr_atm_full_fetch_add(&lock->state, 2);
+  }
+  grpc_closure_list_append(&lock->final_list, closure, error);
+  GPR_TIMER_END("combiner.execute_finally", 0);
+}
+
+void grpc_combiner_force_async_finally(grpc_combiner *lock) {
+  lock->take_async_break_before_final_list = true;
+}
diff --git a/src/core/lib/iomgr/combiner.h b/src/core/lib/iomgr/combiner.h
new file mode 100644
index 0000000000..1409db24b9
--- /dev/null
+++ b/src/core/lib/iomgr/combiner.h
@@ -0,0 +1,71 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_COMBINER_H
+#define GRPC_CORE_LIB_IOMGR_COMBINER_H
+
+#include <stddef.h>
+
+#include <grpc/support/atm.h>
+#include "src/core/lib/iomgr/exec_ctx.h"
+#include "src/core/lib/support/mpscq.h"
+
+// Provides serialized access to some resource.
+// Each action queued on a combiner is executed serially in a borrowed thread.
+// The actual thread executing actions may change over time (but there will only
+// every be one at a time).
+
+// Initialize the lock, with an optional workqueue to shift load to when
+// necessary
+grpc_combiner *grpc_combiner_create(grpc_workqueue *optional_workqueue);
+// Destroy the lock
+void grpc_combiner_destroy(grpc_exec_ctx *exec_ctx, grpc_combiner *lock);
+// Execute \a action within the lock.
+void grpc_combiner_execute(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                           grpc_closure *closure, grpc_error *error);
+// Execute \a action within the lock just prior to unlocking.
+// if \a hint_async_break is true, the combiner tries to hand execution to
+// another thread before finishing the primary queue of combined closures and
+// executing the finally list.
+// Deprecation warning: \a hint_async_break will be removed in a future version
+// Takes a very slow and round-about path if not called from a
+// grpc_combiner_execute closure.
+void grpc_combiner_execute_finally(grpc_exec_ctx *exec_ctx, grpc_combiner *lock,
+                                   grpc_closure *closure, grpc_error *error,
+                                   bool hint_async_break);
+// Deprecated: force the finally list execution onto another thread
+void grpc_combiner_force_async_finally(grpc_combiner *lock);
+
+extern int grpc_combiner_trace;
+
+#endif /* GRPC_CORE_LIB_IOMGR_COMBINER_H */
diff --git a/src/core/lib/iomgr/endpoint.h b/src/core/lib/iomgr/endpoint.h
index 894efc0b23..910a6f6532 100644
--- a/src/core/lib/iomgr/endpoint.h
+++ b/src/core/lib/iomgr/endpoint.h
@@ -64,7 +64,8 @@ struct grpc_endpoint_vtable {
 /* When data is available on the connection, calls the callback with slices.
    Callback success indicates that the endpoint can accept more reads, failure
    indicates the endpoint is closed.
-   Valid slices may be placed into \a slices even on callback success == 0. */
+   Valid slices may be placed into \a slices even when the callback is
+   invoked with error != GRPC_ERROR_NONE. */
 void grpc_endpoint_read(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                         gpr_slice_buffer *slices, grpc_closure *cb);
 
diff --git a/src/core/lib/iomgr/error.c b/src/core/lib/iomgr/error.c
index 149c55663c..31c80260f8 100644
--- a/src/core/lib/iomgr/error.c
+++ b/src/core/lib/iomgr/error.c
@@ -324,6 +324,64 @@ const char *grpc_error_get_str(grpc_error *err, grpc_error_strs which) {
   return gpr_avl_get(err->strs, (void *)(uintptr_t)which);
 }
 
+typedef struct {
+  grpc_error *error;
+  grpc_status_code code;
+  const char *msg;
+} special_error_status_map;
+static special_error_status_map error_status_map[] = {
+    {GRPC_ERROR_NONE, GRPC_STATUS_OK, ""},
+    {GRPC_ERROR_CANCELLED, GRPC_STATUS_CANCELLED, "RPC cancelled"},
+    {GRPC_ERROR_OOM, GRPC_STATUS_RESOURCE_EXHAUSTED, "Out of memory"},
+};
+
+static grpc_error *recursively_find_error_with_status(grpc_error *error,
+                                                      intptr_t *status) {
+  // If the error itself has a status code, return it.
+  if (grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, status)) {
+    return error;
+  }
+  // Otherwise, search through its children.
+  intptr_t key = 0;
+  while (true) {
+    grpc_error *child_error = gpr_avl_get(error->errs, (void *)key++);
+    if (child_error == NULL) break;
+    grpc_error *result =
+        recursively_find_error_with_status(child_error, status);
+    if (result != NULL) return result;
+  }
+  return NULL;
+}
+
+void grpc_error_get_status(grpc_error *error, grpc_status_code *code,
+                           const char **msg) {
+  // Handle special errors via the static map.
+  for (size_t i = 0; i < GPR_ARRAY_SIZE(error_status_map); ++i) {
+    if (error == error_status_map[i].error) {
+      *code = error_status_map[i].code;
+      *msg = error_status_map[i].msg;
+      return;
+    }
+  }
+  // Populate code.
+  // Start with the parent error and recurse through the tree of children
+  // until we find the first one that has a status code.
+  intptr_t status = GRPC_STATUS_UNKNOWN;  // Default in case we don't find one.
+  grpc_error *found_error = recursively_find_error_with_status(error, &status);
+  *code = (grpc_status_code)status;
+  // Now populate msg.
+  // If we found an error with a status code above, use that; otherwise,
+  // fall back to using the parent error.
+  if (found_error == NULL) found_error = error;
+  // If the error has a status message, use it.  Otherwise, fall back to
+  // the error description.
+  *msg = grpc_error_get_str(found_error, GRPC_ERROR_STR_GRPC_MESSAGE);
+  if (*msg == NULL) {
+    *msg = grpc_error_get_str(found_error, GRPC_ERROR_STR_DESCRIPTION);
+    if (*msg == NULL) *msg = "uknown error";  // Just in case.
+  }
+}
+
 grpc_error *grpc_error_add_child(grpc_error *src, grpc_error *child) {
   GPR_TIMER_BEGIN("grpc_error_add_child", 0);
   grpc_error *new = copy_error_and_unref(src);
@@ -332,7 +390,7 @@ grpc_error *grpc_error_add_child(grpc_error *src, grpc_error *child) {
   return new;
 }
 
-static const char *no_error_string = "null";
+static const char *no_error_string = "\"No Error\"";
 static const char *oom_error_string = "\"Out of memory\"";
 static const char *cancelled_error_string = "\"Cancelled\"";
 
diff --git a/src/core/lib/iomgr/error.h b/src/core/lib/iomgr/error.h
index 6c769accdb..7e2fd7a3bd 100644
--- a/src/core/lib/iomgr/error.h
+++ b/src/core/lib/iomgr/error.h
@@ -37,6 +37,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#include <grpc/status.h>
 #include <grpc/support/time.h>
 
 /// Opaque representation of an error.
@@ -175,6 +176,13 @@ grpc_error *grpc_error_set_str(grpc_error *src, grpc_error_strs which,
 /// Returns NULL if the specified string is not set.
 /// Caller does NOT own return value.
 const char *grpc_error_get_str(grpc_error *error, grpc_error_strs which);
+
+/// A utility function to get the status code and message to be returned
+/// to the application.  If not set in the top-level message, looks
+/// through child errors until it finds the first one with these attributes.
+void grpc_error_get_status(grpc_error *error, grpc_status_code *code,
+                           const char **msg);
+
 /// Add a child error: an error that is believed to have contributed to this
 /// error occurring. Allows root causing high level errors from lower level
 /// errors that contributed to them.
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index eba347125e..ab77ebc78b 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -1531,6 +1531,8 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
 
 static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
                            grpc_fd *fd) {
+  GPR_TIMER_BEGIN("pollset_add_fd", 0);
+
   grpc_error *error = GRPC_ERROR_NONE;
 
   gpr_mu_lock(&pollset->mu);
@@ -1643,6 +1645,8 @@ retry:
   gpr_mu_unlock(&pollset->mu);
 
   GRPC_LOG_IF_ERROR("pollset_add_fd", error);
+
+  GPR_TIMER_END("pollset_add_fd", 0);
 }
 
 /*******************************************************************************
@@ -1893,7 +1897,7 @@ const grpc_event_engine_vtable *grpc_init_epoll_linux(void) {
   }
 
   if (!is_grpc_wakeup_signal_initialized) {
-    grpc_use_signal(SIGRTMIN + 2);
+    grpc_use_signal(SIGRTMIN + 6);
   }
 
   fd_global_init();
diff --git a/src/core/lib/iomgr/exec_ctx.h b/src/core/lib/iomgr/exec_ctx.h
index 917f332f03..4d20ecf922 100644
--- a/src/core/lib/iomgr/exec_ctx.h
+++ b/src/core/lib/iomgr/exec_ctx.h
@@ -40,10 +40,9 @@
 
 /** A workqueue represents a list of work to be executed asynchronously.
     Forward declared here to avoid a circular dependency with workqueue.h. */
-struct grpc_workqueue;
 typedef struct grpc_workqueue grpc_workqueue;
+typedef struct grpc_combiner grpc_combiner;
 
-#ifndef GRPC_EXECUTION_CONTEXT_SANITIZER
 /** Execution context.
  *  A bag of data that collects information along a callstack.
  *  Generally created at public API entry points, and passed down as
@@ -58,21 +57,24 @@ typedef struct grpc_workqueue grpc_workqueue;
  *    should actively try to finish up and get this thread back to its owner
  *
  *  CONVENTIONS:
- *  Instance of this must ALWAYS be constructed on the stack, never
- *  heap allocated. Instances and pointers to them must always be called
- *  exec_ctx. Instances are always passed as the first argument
- *  to a function that takes it, and always as a pointer (grpc_exec_ctx
- *  is never copied).
+ *  - Instance of this must ALWAYS be constructed on the stack, never
+ *    heap allocated.
+ *  - Instances and pointers to them must always be called exec_ctx.
+ *  - Instances are always passed as the first argument to a function that
+ *    takes it, and always as a pointer (grpc_exec_ctx is never copied).
  */
+#ifndef GRPC_EXECUTION_CONTEXT_SANITIZER
 struct grpc_exec_ctx {
   grpc_closure_list closure_list;
+  /** currently active combiner: updated only via combiner.c */
+  grpc_combiner *active_combiner;
   bool cached_ready_to_finish;
   void *check_ready_to_finish_arg;
   bool (*check_ready_to_finish)(grpc_exec_ctx *exec_ctx, void *arg);
 };
 
 #define GRPC_EXEC_CTX_INIT_WITH_FINISH_CHECK(finish_check, finish_check_arg) \
-  { GRPC_CLOSURE_LIST_INIT, false, finish_check_arg, finish_check }
+  { GRPC_CLOSURE_LIST_INIT, NULL, false, finish_check_arg, finish_check }
 #else
 struct grpc_exec_ctx {
   bool cached_ready_to_finish;
diff --git a/src/core/lib/iomgr/socket_windows.c b/src/core/lib/iomgr/socket_windows.c
index d7d5f6f157..78ef46d042 100644
--- a/src/core/lib/iomgr/socket_windows.c
+++ b/src/core/lib/iomgr/socket_windows.c
@@ -84,7 +84,7 @@ void grpc_winsocket_shutdown(grpc_winsocket *winsocket) {
     DisconnectEx(winsocket->socket, NULL, 0, 0);
   } else {
     char *utf8_message = gpr_format_message(WSAGetLastError());
-    gpr_log(GPR_ERROR, "Unable to retrieve DisconnectEx pointer : %s",
+    gpr_log(GPR_INFO, "Unable to retrieve DisconnectEx pointer : %s",
             utf8_message);
     gpr_free(utf8_message);
   }
diff --git a/src/core/lib/iomgr/tcp_client_posix.c b/src/core/lib/iomgr/tcp_client_posix.c
index 80c7a3f128..3496b6094f 100644
--- a/src/core/lib/iomgr/tcp_client_posix.c
+++ b/src/core/lib/iomgr/tcp_client_posix.c
@@ -146,61 +146,57 @@ static void on_writable(grpc_exec_ctx *exec_ctx, void *acp, grpc_error *error) {
   grpc_timer_cancel(exec_ctx, &ac->alarm);
 
   gpr_mu_lock(&ac->mu);
-  if (error == GRPC_ERROR_NONE) {
-    do {
-      so_error_size = sizeof(so_error);
-      err = getsockopt(grpc_fd_wrapped_fd(fd), SOL_SOCKET, SO_ERROR, &so_error,
-                       &so_error_size);
-    } while (err < 0 && errno == EINTR);
-    if (err < 0) {
-      error = GRPC_OS_ERROR(errno, "getsockopt");
-      goto finish;
-    } else if (so_error != 0) {
-      if (so_error == ENOBUFS) {
-        /* We will get one of these errors if we have run out of
-           memory in the kernel for the data structures allocated
-           when you connect a socket.  If this happens it is very
-           likely that if we wait a little bit then try again the
-           connection will work (since other programs or this
-           program will close their network connections and free up
-           memory).  This does _not_ indicate that there is anything
-           wrong with the server we are connecting to, this is a
-           local problem.
-
-           If you are looking at this code, then chances are that
-           your program or another program on the same computer
-           opened too many network connections.  The "easy" fix:
-           don't do that! */
-        gpr_log(GPR_ERROR, "kernel out of buffers");
-        gpr_mu_unlock(&ac->mu);
-        grpc_fd_notify_on_write(exec_ctx, fd, &ac->write_closure);
-        return;
-      } else {
-        switch (so_error) {
-          case ECONNREFUSED:
-            error = grpc_error_set_int(error, GRPC_ERROR_INT_ERRNO, errno);
-            error = grpc_error_set_str(error, GRPC_ERROR_STR_OS_ERROR,
-                                       "Connection refused");
-            break;
-          default:
-            error = GRPC_OS_ERROR(errno, "getsockopt(SO_ERROR)");
-            break;
-        }
-        goto finish;
-      }
-    } else {
-      grpc_pollset_set_del_fd(exec_ctx, ac->interested_parties, fd);
-      *ep = grpc_tcp_create(fd, GRPC_TCP_DEFAULT_READ_SLICE_SIZE, ac->addr_str);
-      fd = NULL;
-      goto finish;
-    }
-  } else {
+  if (error != GRPC_ERROR_NONE) {
     error =
         grpc_error_set_str(error, GRPC_ERROR_STR_OS_ERROR, "Timeout occurred");
     goto finish;
   }
 
-  GPR_UNREACHABLE_CODE(return );
+  do {
+    so_error_size = sizeof(so_error);
+    err = getsockopt(grpc_fd_wrapped_fd(fd), SOL_SOCKET, SO_ERROR, &so_error,
+                     &so_error_size);
+  } while (err < 0 && errno == EINTR);
+  if (err < 0) {
+    error = GRPC_OS_ERROR(errno, "getsockopt");
+    goto finish;
+  }
+
+  switch (so_error) {
+    case 0:
+      grpc_pollset_set_del_fd(exec_ctx, ac->interested_parties, fd);
+      *ep = grpc_tcp_create(fd, GRPC_TCP_DEFAULT_READ_SLICE_SIZE, ac->addr_str);
+      fd = NULL;
+      break;
+    case ENOBUFS:
+      /* We will get one of these errors if we have run out of
+         memory in the kernel for the data structures allocated
+         when you connect a socket.  If this happens it is very
+         likely that if we wait a little bit then try again the
+         connection will work (since other programs or this
+         program will close their network connections and free up
+         memory).  This does _not_ indicate that there is anything
+         wrong with the server we are connecting to, this is a
+         local problem.
+
+         If you are looking at this code, then chances are that
+         your program or another program on the same computer
+         opened too many network connections.  The "easy" fix:
+         don't do that! */
+      gpr_log(GPR_ERROR, "kernel out of buffers");
+      gpr_mu_unlock(&ac->mu);
+      grpc_fd_notify_on_write(exec_ctx, fd, &ac->write_closure);
+      return;
+    case ECONNREFUSED:
+      /* This error shouldn't happen for anything other than connect(). */
+      error = GRPC_OS_ERROR(so_error, "connect");
+      break;
+    default:
+      /* We don't really know which syscall triggered the problem here,
+         so punt by reporting getsockopt(). */
+      error = GRPC_OS_ERROR(so_error, "getsockopt(SO_ERROR)");
+      break;
+  }
 
 finish:
   if (fd != NULL) {
diff --git a/src/core/lib/iomgr/tcp_posix.c b/src/core/lib/iomgr/tcp_posix.c
index 974d5ae479..92767721d5 100644
--- a/src/core/lib/iomgr/tcp_posix.c
+++ b/src/core/lib/iomgr/tcp_posix.c
@@ -379,10 +379,19 @@ static void tcp_handle_write(grpc_exec_ctx *exec_ctx, void *arg /* grpc_tcp */,
   }
 
   if (!tcp_flush(tcp, &error)) {
+    if (grpc_tcp_trace) {
+      gpr_log(GPR_DEBUG, "write: delayed");
+    }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
     cb = tcp->write_cb;
     tcp->write_cb = NULL;
+    if (grpc_tcp_trace) {
+      const char *str = grpc_error_string(error);
+      gpr_log(GPR_DEBUG, "write: %s", str);
+      grpc_error_free_string(str);
+    }
+
     GPR_TIMER_BEGIN("tcp_handle_write.cb", 0);
     cb->cb(exec_ctx, cb->cb_arg, error);
     GPR_TIMER_END("tcp_handle_write.cb", 0);
@@ -425,8 +434,16 @@ static void tcp_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   if (!tcp_flush(tcp, &error)) {
     TCP_REF(tcp, "write");
     tcp->write_cb = cb;
+    if (grpc_tcp_trace) {
+      gpr_log(GPR_DEBUG, "write: delayed");
+    }
     grpc_fd_notify_on_write(exec_ctx, tcp->em_fd, &tcp->write_closure);
   } else {
+    if (grpc_tcp_trace) {
+      const char *str = grpc_error_string(error);
+      gpr_log(GPR_DEBUG, "write: %s", str);
+      grpc_error_free_string(str);
+    }
     grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
   }
 
diff --git a/src/core/lib/iomgr/tcp_windows.c b/src/core/lib/iomgr/tcp_windows.c
index 35054c42b5..448a72671c 100644
--- a/src/core/lib/iomgr/tcp_windows.c
+++ b/src/core/lib/iomgr/tcp_windows.c
@@ -319,6 +319,7 @@ static void win_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
                             ? GRPC_ERROR_NONE
                             : GRPC_WSA_ERROR(info->wsa_error, "WSASend");
     grpc_exec_ctx_sched(exec_ctx, cb, error, NULL);
+    if (allocated) gpr_free(allocated);
     return;
   }
 
diff --git a/src/core/lib/iomgr/workqueue.h b/src/core/lib/iomgr/workqueue.h
index 7156e490d7..b2805dc66c 100644
--- a/src/core/lib/iomgr/workqueue.h
+++ b/src/core/lib/iomgr/workqueue.h
@@ -50,10 +50,6 @@
 
 /* grpc_workqueue is forward declared in exec_ctx.h */
 
-/* Deprecated: do not use.
-   This has *already* been removed in a future commit. */
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue);
-
 /* Reference counting functions. Use the macro's always
    (GRPC_WORKQUEUE_{REF,UNREF}).
 
diff --git a/src/core/lib/iomgr/workqueue_posix.c b/src/core/lib/iomgr/workqueue_posix.c
index e0d6dac230..ecfea68f56 100644
--- a/src/core/lib/iomgr/workqueue_posix.c
+++ b/src/core/lib/iomgr/workqueue_posix.c
@@ -44,6 +44,7 @@
 #include <grpc/support/useful.h>
 
 #include "src/core/lib/iomgr/ev_posix.h"
+#include "src/core/lib/profiling/timers.h"
 
 static void on_readable(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error);
 
@@ -52,8 +53,7 @@ grpc_error *grpc_workqueue_create(grpc_exec_ctx *exec_ctx,
   char name[32];
   *workqueue = gpr_malloc(sizeof(grpc_workqueue));
   gpr_ref_init(&(*workqueue)->refs, 1);
-  gpr_mu_init(&(*workqueue)->mu);
-  (*workqueue)->closure_list.head = (*workqueue)->closure_list.tail = NULL;
+  gpr_atm_no_barrier_store(&(*workqueue)->state, 1);
   grpc_error *err = grpc_wakeup_fd_init(&(*workqueue)->wakeup_fd);
   if (err != GRPC_ERROR_NONE) {
     gpr_free(*workqueue);
@@ -62,6 +62,7 @@ grpc_error *grpc_workqueue_create(grpc_exec_ctx *exec_ctx,
   sprintf(name, "workqueue:%p", (void *)(*workqueue));
   (*workqueue)->wakeup_read_fd = grpc_fd_create(
       GRPC_WAKEUP_FD_GET_READ_FD(&(*workqueue)->wakeup_fd), name);
+  gpr_mpscq_init(&(*workqueue)->queue);
   grpc_closure_init(&(*workqueue)->read_closure, on_readable, *workqueue);
   grpc_fd_notify_on_read(exec_ctx, (*workqueue)->wakeup_read_fd,
                          &(*workqueue)->read_closure);
@@ -70,57 +71,79 @@ grpc_error *grpc_workqueue_create(grpc_exec_ctx *exec_ctx,
 
 static void workqueue_destroy(grpc_exec_ctx *exec_ctx,
                               grpc_workqueue *workqueue) {
-  grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
   grpc_fd_shutdown(exec_ctx, workqueue->wakeup_read_fd);
 }
 
+static void workqueue_orphan(grpc_exec_ctx *exec_ctx,
+                             grpc_workqueue *workqueue) {
+  if (gpr_atm_full_fetch_add(&workqueue->state, -1) == 1) {
+    workqueue_destroy(exec_ctx, workqueue);
+  }
+}
+
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_ref(grpc_workqueue *workqueue, const char *file, int line,
                         const char *reason) {
+  if (workqueue == NULL) return;
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "WORKQUEUE:%p   ref %d -> %d %s",
           workqueue, (int)workqueue->refs.count, (int)workqueue->refs.count + 1,
           reason);
+  gpr_ref(&workqueue->refs);
+}
 #else
 void grpc_workqueue_ref(grpc_workqueue *workqueue) {
-#endif
+  if (workqueue == NULL) return;
   gpr_ref(&workqueue->refs);
 }
+#endif
 
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
                           const char *file, int line, const char *reason) {
+  if (workqueue == NULL) return;
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG, "WORKQUEUE:%p unref %d -> %d %s",
           workqueue, (int)workqueue->refs.count, (int)workqueue->refs.count - 1,
           reason);
+  if (gpr_unref(&workqueue->refs)) {
+    workqueue_orphan(exec_ctx, workqueue);
+  }
+}
 #else
 void grpc_workqueue_unref(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
-#endif
+  if (workqueue == NULL) return;
   if (gpr_unref(&workqueue->refs)) {
-    workqueue_destroy(exec_ctx, workqueue);
+    workqueue_orphan(exec_ctx, workqueue);
   }
 }
+#endif
+
+static void drain(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
+  abort();
+}
 
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
-  gpr_mu_lock(&workqueue->mu);
-  grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
-  gpr_mu_unlock(&workqueue->mu);
+static void wakeup(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {
+  GPR_TIMER_MARK("workqueue.wakeup", 0);
+  grpc_error *err = grpc_wakeup_fd_wakeup(&workqueue->wakeup_fd);
+  if (!GRPC_LOG_IF_ERROR("wakeupfd_wakeup", err)) {
+    drain(exec_ctx, workqueue);
+  }
 }
 
 static void on_readable(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  GPR_TIMER_BEGIN("workqueue.on_readable", 0);
+
   grpc_workqueue *workqueue = arg;
 
   if (error != GRPC_ERROR_NONE) {
-    gpr_mu_destroy(&workqueue->mu);
     /* HACK: let wakeup_fd code know that we stole the fd */
     workqueue->wakeup_fd.read_fd = 0;
     grpc_wakeup_fd_destroy(&workqueue->wakeup_fd);
     grpc_fd_orphan(exec_ctx, workqueue->wakeup_read_fd, NULL, NULL, "destroy");
+    GPR_ASSERT(gpr_atm_no_barrier_load(&workqueue->state) == 0);
     gpr_free(workqueue);
   } else {
-    gpr_mu_lock(&workqueue->mu);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
     error = grpc_wakeup_fd_consume_wakeup(&workqueue->wakeup_fd);
-    gpr_mu_unlock(&workqueue->mu);
+    gpr_mpscq_node *n = gpr_mpscq_pop(&workqueue->queue);
     if (error == GRPC_ERROR_NONE) {
       grpc_fd_notify_on_read(exec_ctx, workqueue->wakeup_read_fd,
                              &workqueue->read_closure);
@@ -128,24 +151,46 @@ static void on_readable(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
       /* recurse to get error handling */
       on_readable(exec_ctx, arg, error);
     }
+    if (n == NULL) {
+      /* try again - queue in an inconsistant state */
+      wakeup(exec_ctx, workqueue);
+    } else {
+      switch (gpr_atm_full_fetch_add(&workqueue->state, -2)) {
+        case 3:  // had one count, one unorphaned --> done, unorphaned
+          break;
+        case 2:  // had one count, one orphaned --> done, orphaned
+          workqueue_destroy(exec_ctx, workqueue);
+          break;
+        case 1:
+        case 0:
+          // these values are illegal - representing an already done or
+          // deleted workqueue
+          GPR_UNREACHABLE_CODE(break);
+        default:
+          // schedule a wakeup since there's more to do
+          wakeup(exec_ctx, workqueue);
+      }
+      grpc_closure *cl = (grpc_closure *)n;
+      grpc_error *clerr = cl->error;
+      cl->cb(exec_ctx, cl->cb_arg, clerr);
+      GRPC_ERROR_UNREF(clerr);
+    }
   }
+
+  GPR_TIMER_END("workqueue.on_readable", 0);
 }
 
 void grpc_workqueue_enqueue(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue,
                             grpc_closure *closure, grpc_error *error) {
-  grpc_error *push_error = GRPC_ERROR_NONE;
-  gpr_mu_lock(&workqueue->mu);
-  if (grpc_closure_list_empty(workqueue->closure_list)) {
-    push_error = grpc_wakeup_fd_wakeup(&workqueue->wakeup_fd);
-  }
-  grpc_closure_list_append(&workqueue->closure_list, closure, error);
-  if (push_error != GRPC_ERROR_NONE) {
-    const char *msg = grpc_error_string(push_error);
-    gpr_log(GPR_ERROR, "Failed to push to workqueue: %s", msg);
-    grpc_error_free_string(msg);
-    grpc_exec_ctx_enqueue_list(exec_ctx, &workqueue->closure_list, NULL);
+  GPR_TIMER_BEGIN("workqueue.enqueue", 0);
+  gpr_atm last = gpr_atm_full_fetch_add(&workqueue->state, 2);
+  GPR_ASSERT(last & 1);
+  closure->error = error;
+  gpr_mpscq_push(&workqueue->queue, &closure->next_data.atm_next);
+  if (last == 1) {
+    wakeup(exec_ctx, workqueue);
   }
-  gpr_mu_unlock(&workqueue->mu);
+  GPR_TIMER_END("workqueue.enqueue", 0);
 }
 
 #endif /* GPR_POSIX_SOCKET */
diff --git a/src/core/lib/iomgr/workqueue_posix.h b/src/core/lib/iomgr/workqueue_posix.h
index 0f26ba58e2..03ee21cef7 100644
--- a/src/core/lib/iomgr/workqueue_posix.h
+++ b/src/core/lib/iomgr/workqueue_posix.h
@@ -35,14 +35,17 @@
 #define GRPC_CORE_LIB_IOMGR_WORKQUEUE_POSIX_H
 
 #include "src/core/lib/iomgr/wakeup_fd_posix.h"
+#include "src/core/lib/support/mpscq.h"
 
 struct grpc_fd;
 
 struct grpc_workqueue {
   gpr_refcount refs;
-
-  gpr_mu mu;
-  grpc_closure_list closure_list;
+  gpr_mpscq queue;
+  // state is:
+  // lower bit - zero if orphaned
+  // other bits - number of items enqueued
+  gpr_atm state;
 
   grpc_wakeup_fd wakeup_fd;
   struct grpc_fd *wakeup_read_fd;
diff --git a/src/core/lib/iomgr/workqueue_windows.c b/src/core/lib/iomgr/workqueue_windows.c
index 23e2dea185..ee81dc248e 100644
--- a/src/core/lib/iomgr/workqueue_windows.c
+++ b/src/core/lib/iomgr/workqueue_windows.c
@@ -42,8 +42,6 @@
 // context, which is at least correct, if not performant or in the spirit of
 // workqueues.
 
-void grpc_workqueue_flush(grpc_exec_ctx *exec_ctx, grpc_workqueue *workqueue) {}
-
 #ifdef GRPC_WORKQUEUE_REFCOUNT_DEBUG
 void grpc_workqueue_ref(grpc_workqueue *workqueue, const char *file, int line,
                         const char *reason) {}
diff --git a/src/core/lib/security/credentials/jwt/json_token.c b/src/core/lib/security/credentials/jwt/json_token.c
index 354c13133e..192a5f47ed 100644
--- a/src/core/lib/security/credentials/jwt/json_token.c
+++ b/src/core/lib/security/credentials/jwt/json_token.c
@@ -38,6 +38,7 @@
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
+#include <grpc/support/time.h>
 
 #include "src/core/lib/security/util/b64.h"
 #include "src/core/lib/security/util/json_util.h"
diff --git a/src/core/lib/security/credentials/plugin/plugin_credentials.c b/src/core/lib/security/credentials/plugin/plugin_credentials.c
index 824ff081dc..905de3723e 100644
--- a/src/core/lib/security/credentials/plugin/plugin_credentials.c
+++ b/src/core/lib/security/credentials/plugin/plugin_credentials.c
@@ -37,6 +37,7 @@
 
 #include "src/core/lib/surface/api_trace.h"
 
+#include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
 #include <grpc/support/string_util.h>
@@ -71,17 +72,33 @@ static void plugin_md_request_metadata_ready(void *request,
           error_details);
   } else {
     size_t i;
+    bool seen_illegal_header = false;
     grpc_credentials_md *md_array = NULL;
-    if (num_md > 0) {
+    for (i = 0; i < num_md; i++) {
+      if (!grpc_header_key_is_legal(md[i].key, strlen(md[i].key))) {
+        gpr_log(GPR_ERROR, "Plugin added invalid metadata key: %s", md[i].key);
+        seen_illegal_header = true;
+        break;
+      } else if (!grpc_is_binary_header(md[i].key, strlen(md[i].key)) &&
+                 !grpc_header_nonbin_value_is_legal(md[i].value,
+                                                    md[i].value_length)) {
+        gpr_log(GPR_ERROR, "Plugin added invalid metadata value.");
+        seen_illegal_header = true;
+        break;
+      }
+    }
+    if (seen_illegal_header) {
+      r->cb(&exec_ctx, r->user_data, NULL, 0, GRPC_CREDENTIALS_ERROR,
+            "Illegal metadata");
+    } else if (num_md > 0) {
       md_array = gpr_malloc(num_md * sizeof(grpc_credentials_md));
       for (i = 0; i < num_md; i++) {
         md_array[i].key = gpr_slice_from_copied_string(md[i].key);
         md_array[i].value =
             gpr_slice_from_copied_buffer(md[i].value, md[i].value_length);
       }
-    }
-    r->cb(&exec_ctx, r->user_data, md_array, num_md, GRPC_CREDENTIALS_OK, NULL);
-    if (md_array != NULL) {
+      r->cb(&exec_ctx, r->user_data, md_array, num_md, GRPC_CREDENTIALS_OK,
+            NULL);
       for (i = 0; i < num_md; i++) {
         gpr_slice_unref(md_array[i].key);
         gpr_slice_unref(md_array[i].value);
diff --git a/src/core/lib/security/transport/client_auth_filter.c b/src/core/lib/security/transport/client_auth_filter.c
index 2a1bf4d4e3..b366d1410f 100644
--- a/src/core/lib/security/transport/client_auth_filter.c
+++ b/src/core/lib/security/transport/client_auth_filter.c
@@ -40,6 +40,7 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/lib/channel/channel_stack.h"
+#include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/security/context/security_context.h"
 #include "src/core/lib/security/credentials/credentials.h"
 #include "src/core/lib/security/transport/security_connector.h"
@@ -218,6 +219,8 @@ static void on_host_checked(grpc_exec_ctx *exec_ctx, void *user_data,
 static void auth_start_transport_op(grpc_exec_ctx *exec_ctx,
                                     grpc_call_element *elem,
                                     grpc_transport_stream_op *op) {
+  GPR_TIMER_BEGIN("auth_start_transport_op", 0);
+
   /* grab pointers to our data from the call element */
   call_data *calld = elem->call_data;
   channel_data *chand = elem->channel_data;
@@ -258,12 +261,14 @@ static void auth_start_transport_op(grpc_exec_ctx *exec_ctx,
       grpc_channel_security_connector_check_call_host(
           exec_ctx, chand->security_connector, call_host, chand->auth_context,
           on_host_checked, elem);
+      GPR_TIMER_END("auth_start_transport_op", 0);
       return; /* early exit */
     }
   }
 
   /* pass control down the stack */
   grpc_call_next_op(exec_ctx, elem, op);
+  GPR_TIMER_END("auth_start_transport_op", 0);
 }
 
 /* Constructor for call_data */
diff --git a/src/core/lib/security/transport/secure_endpoint.c b/src/core/lib/security/transport/secure_endpoint.c
index 0169ccd9ef..acb0113ea8 100644
--- a/src/core/lib/security/transport/secure_endpoint.c
+++ b/src/core/lib/security/transport/secure_endpoint.c
@@ -38,6 +38,7 @@
 #include <grpc/support/slice_buffer.h>
 #include <grpc/support/sync.h>
 #include "src/core/lib/debug/trace.h"
+#include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/security/transport/tsi_error.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/tsi/transport_security_interface.h"
@@ -248,6 +249,8 @@ static void flush_write_staging_buffer(secure_endpoint *ep, uint8_t **cur,
 
 static void endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *secure_ep,
                            gpr_slice_buffer *slices, grpc_closure *cb) {
+  GPR_TIMER_BEGIN("secure_endpoint.endpoint_write", 0);
+
   unsigned i;
   tsi_result result = TSI_OK;
   secure_endpoint *ep = (secure_endpoint *)secure_ep;
@@ -323,10 +326,12 @@ static void endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *secure_ep,
         exec_ctx, cb,
         grpc_set_tsi_error_result(GRPC_ERROR_CREATE("Wrap failed"), result),
         NULL);
+    GPR_TIMER_END("secure_endpoint.endpoint_write", 0);
     return;
   }
 
   grpc_endpoint_write(exec_ctx, ep->wrapped_ep, &ep->output_buffer, cb);
+  GPR_TIMER_END("secure_endpoint.endpoint_write", 0);
 }
 
 static void endpoint_shutdown(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/security/transport/server_auth_filter.c b/src/core/lib/security/transport/server_auth_filter.c
index def16c8229..b2c6815af8 100644
--- a/src/core/lib/security/transport/server_auth_filter.c
+++ b/src/core/lib/security/transport/server_auth_filter.c
@@ -48,7 +48,7 @@ typedef struct call_data {
      up-call on transport_op, and remember to call our on_done_recv member after
      handling it. */
   grpc_closure auth_on_recv;
-  grpc_transport_stream_op transport_op;
+  grpc_transport_stream_op *transport_op;
   grpc_metadata_array md;
   const grpc_metadata *consumed_md;
   size_t num_consumed_md;
@@ -106,6 +106,10 @@ static grpc_mdelem *remove_consumed_md(void *user_data, grpc_mdelem *md) {
   return md;
 }
 
+static void destroy_op(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
+  gpr_free(arg);
+}
+
 /* called from application code */
 static void on_md_processing_done(
     void *user_data, const grpc_metadata *consumed_md, size_t num_consumed_md,
@@ -131,21 +135,22 @@ static void on_md_processing_done(
     grpc_exec_ctx_sched(&exec_ctx, calld->on_done_recv, GRPC_ERROR_NONE, NULL);
   } else {
     gpr_slice message;
-    grpc_transport_stream_op close_op;
-    memset(&close_op, 0, sizeof(close_op));
+    grpc_transport_stream_op *close_op = gpr_malloc(sizeof(*close_op));
+    memset(close_op, 0, sizeof(*close_op));
     grpc_metadata_array_destroy(&calld->md);
     error_details = error_details != NULL
                         ? error_details
                         : "Authentication metadata processing failed.";
     message = gpr_slice_from_copied_string(error_details);
-    calld->transport_op.send_initial_metadata = NULL;
-    if (calld->transport_op.send_message != NULL) {
-      grpc_byte_stream_destroy(&exec_ctx, calld->transport_op.send_message);
-      calld->transport_op.send_message = NULL;
+    calld->transport_op->send_initial_metadata = NULL;
+    if (calld->transport_op->send_message != NULL) {
+      grpc_byte_stream_destroy(&exec_ctx, calld->transport_op->send_message);
+      calld->transport_op->send_message = NULL;
     }
-    calld->transport_op.send_trailing_metadata = NULL;
-    grpc_transport_stream_op_add_close(&close_op, status, &message);
-    grpc_call_next_op(&exec_ctx, elem, &close_op);
+    calld->transport_op->send_trailing_metadata = NULL;
+    close_op->on_complete = grpc_closure_create(destroy_op, close_op);
+    grpc_transport_stream_op_add_close(close_op, status, &message);
+    grpc_call_next_op(&exec_ctx, elem, close_op);
     grpc_exec_ctx_sched(&exec_ctx, calld->on_done_recv,
                         grpc_error_set_int(GRPC_ERROR_CREATE(error_details),
                                            GRPC_ERROR_INT_GRPC_STATUS, status),
@@ -182,7 +187,7 @@ static void set_recv_ops_md_callbacks(grpc_call_element *elem,
     calld->recv_initial_metadata = op->recv_initial_metadata;
     calld->on_done_recv = op->recv_initial_metadata_ready;
     op->recv_initial_metadata_ready = &calld->auth_on_recv;
-    calld->transport_op = *op;
+    calld->transport_op = op;
   }
 }
 
diff --git a/src/core/lib/support/log_posix.c b/src/core/lib/support/log_posix.c
index 6ae6320767..f972da0887 100644
--- a/src/core/lib/support/log_posix.c
+++ b/src/core/lib/support/log_posix.c
@@ -33,7 +33,7 @@
 
 #include <grpc/support/port_platform.h>
 
-#if defined(GPR_POSIX_LOG)
+#ifdef GPR_POSIX_LOG
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
diff --git a/src/core/lib/support/mpscq.c b/src/core/lib/support/mpscq.c
new file mode 100644
index 0000000000..5b9323275a
--- /dev/null
+++ b/src/core/lib/support/mpscq.c
@@ -0,0 +1,83 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/support/mpscq.h"
+
+#include <grpc/support/log.h>
+
+void gpr_mpscq_init(gpr_mpscq *q) {
+  gpr_atm_no_barrier_store(&q->head, (gpr_atm)&q->stub);
+  q->tail = &q->stub;
+  gpr_atm_no_barrier_store(&q->stub.next, (gpr_atm)NULL);
+}
+
+void gpr_mpscq_destroy(gpr_mpscq *q) {
+  GPR_ASSERT(gpr_atm_no_barrier_load(&q->head) == (gpr_atm)&q->stub);
+  GPR_ASSERT(q->tail == &q->stub);
+}
+
+void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n) {
+  gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
+  gpr_mpscq_node *prev =
+      (gpr_mpscq_node *)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
+  gpr_atm_rel_store(&prev->next, (gpr_atm)n);
+}
+
+gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
+  gpr_mpscq_node *tail = q->tail;
+  gpr_mpscq_node *next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (tail == &q->stub) {
+    // indicates the list is actually (ephemerally) empty
+    if (next == NULL) return NULL;
+    q->tail = next;
+    tail = next;
+    next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  }
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  gpr_mpscq_node *head = (gpr_mpscq_node *)gpr_atm_acq_load(&q->head);
+  if (tail != head) {
+    // indicates a retry is in order: we're still adding
+    return NULL;
+  }
+  gpr_mpscq_push(q, &q->stub);
+  next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
+  if (next != NULL) {
+    q->tail = next;
+    return tail;
+  }
+  // indicates a retry is in order: we're still adding
+  return NULL;
+}
diff --git a/src/core/lib/support/mpscq.h b/src/core/lib/support/mpscq.h
new file mode 100644
index 0000000000..977a117952
--- /dev/null
+++ b/src/core/lib/support/mpscq.h
@@ -0,0 +1,65 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_SUPPORT_MPSCQ_H
+#define GRPC_CORE_LIB_SUPPORT_MPSCQ_H
+
+#include <grpc/support/atm.h>
+#include <stddef.h>
+
+// Multiple-producer single-consumer lock free queue, based upon the
+// implementation from Dmitry Vyukov here:
+// http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
+
+// List node (include this in a data structure at the top, and add application
+// fields after it - to simulate inheritance)
+typedef struct gpr_mpscq_node { gpr_atm next; } gpr_mpscq_node;
+
+// Actual queue type
+typedef struct gpr_mpscq {
+  gpr_atm head;
+  // make sure head & tail don't share a cacheline
+  char padding[GPR_CACHELINE_SIZE];
+  gpr_mpscq_node *tail;
+  gpr_mpscq_node stub;
+} gpr_mpscq;
+
+void gpr_mpscq_init(gpr_mpscq *q);
+void gpr_mpscq_destroy(gpr_mpscq *q);
+// Push a node
+void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n);
+// Pop a node (returns NULL if no node is ready - which doesn't indicate that
+// the queue is empty!!)
+gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q);
+
+#endif /* GRPC_CORE_LIB_SUPPORT_MPSCQ_H */
diff --git a/src/core/lib/support/percent_encoding.c b/src/core/lib/support/percent_encoding.c
new file mode 100644
index 0000000000..3c19f264f9
--- /dev/null
+++ b/src/core/lib/support/percent_encoding.c
@@ -0,0 +1,180 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include "src/core/lib/support/percent_encoding.h"
+
+#include <grpc/support/log.h>
+
+const uint8_t gpr_url_percent_encoding_unreserved_bytes[256 / 8] = {
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x60, 0xff, 0x03, 0xfe, 0xff, 0xff,
+    0x87, 0xfe, 0xff, 0xff, 0x47, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+const uint8_t gpr_compatible_percent_encoding_unreserved_bytes[256 / 8] = {
+    0x00, 0x00, 0x00, 0x00, 0xdf, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+static bool is_unreserved_character(uint8_t c,
+                                    const uint8_t *unreserved_bytes) {
+  return ((unreserved_bytes[c / 8] >> (c % 8)) & 1) != 0;
+}
+
+gpr_slice gpr_percent_encode_slice(gpr_slice slice,
+                                   const uint8_t *unreserved_bytes) {
+  static const uint8_t hex[] = "0123456789ABCDEF";
+
+  // first pass: count the number of bytes needed to output this string
+  size_t output_length = 0;
+  const uint8_t *slice_start = GPR_SLICE_START_PTR(slice);
+  const uint8_t *slice_end = GPR_SLICE_END_PTR(slice);
+  const uint8_t *p;
+  bool any_reserved_bytes = false;
+  for (p = slice_start; p < slice_end; p++) {
+    bool unres = is_unreserved_character(*p, unreserved_bytes);
+    output_length += unres ? 1 : 3;
+    any_reserved_bytes |= !unres;
+  }
+  // no unreserved bytes: return the string unmodified
+  if (!any_reserved_bytes) {
+    return gpr_slice_ref(slice);
+  }
+  // second pass: actually encode
+  gpr_slice out = gpr_slice_malloc(output_length);
+  uint8_t *q = GPR_SLICE_START_PTR(out);
+  for (p = slice_start; p < slice_end; p++) {
+    if (is_unreserved_character(*p, unreserved_bytes)) {
+      *q++ = *p;
+    } else {
+      *q++ = '%';
+      *q++ = hex[*p >> 4];
+      *q++ = hex[*p & 15];
+    }
+  }
+  GPR_ASSERT(q == GPR_SLICE_END_PTR(out));
+  return out;
+}
+
+static bool valid_hex(const uint8_t *p, const uint8_t *end) {
+  if (p >= end) return false;
+  return (*p >= '0' && *p <= '9') || (*p >= 'a' && *p <= 'f') ||
+         (*p >= 'A' && *p <= 'F');
+}
+
+static uint8_t dehex(uint8_t c) {
+  if (c >= '0' && c <= '9') return (uint8_t)(c - '0');
+  if (c >= 'A' && c <= 'F') return (uint8_t)(c - 'A' + 10);
+  if (c >= 'a' && c <= 'f') return (uint8_t)(c - 'a' + 10);
+  GPR_UNREACHABLE_CODE(return 255);
+}
+
+bool gpr_strict_percent_decode_slice(gpr_slice slice_in,
+                                     const uint8_t *unreserved_bytes,
+                                     gpr_slice *slice_out) {
+  const uint8_t *p = GPR_SLICE_START_PTR(slice_in);
+  const uint8_t *in_end = GPR_SLICE_END_PTR(slice_in);
+  size_t out_length = 0;
+  bool any_percent_encoded_stuff = false;
+  while (p != in_end) {
+    if (*p == '%') {
+      if (!valid_hex(++p, in_end)) return false;
+      if (!valid_hex(++p, in_end)) return false;
+      p++;
+      out_length++;
+      any_percent_encoded_stuff = true;
+    } else if (is_unreserved_character(*p, unreserved_bytes)) {
+      p++;
+      out_length++;
+    } else {
+      return false;
+    }
+  }
+  if (!any_percent_encoded_stuff) {
+    *slice_out = gpr_slice_ref(slice_in);
+    return true;
+  }
+  p = GPR_SLICE_START_PTR(slice_in);
+  *slice_out = gpr_slice_malloc(out_length);
+  uint8_t *q = GPR_SLICE_START_PTR(*slice_out);
+  while (p != in_end) {
+    if (*p == '%') {
+      *q++ = (uint8_t)(dehex(p[1]) << 4) | (dehex(p[2]));
+      p += 3;
+    } else {
+      *q++ = *p++;
+    }
+  }
+  GPR_ASSERT(q == GPR_SLICE_END_PTR(*slice_out));
+  return true;
+}
+
+gpr_slice gpr_permissive_percent_decode_slice(gpr_slice slice_in) {
+  const uint8_t *p = GPR_SLICE_START_PTR(slice_in);
+  const uint8_t *in_end = GPR_SLICE_END_PTR(slice_in);
+  size_t out_length = 0;
+  bool any_percent_encoded_stuff = false;
+  while (p != in_end) {
+    if (*p == '%') {
+      if (!valid_hex(p + 1, in_end) || !valid_hex(p + 2, in_end)) {
+        p++;
+        out_length++;
+      } else {
+        p += 3;
+        out_length++;
+        any_percent_encoded_stuff = true;
+      }
+    } else {
+      p++;
+      out_length++;
+    }
+  }
+  if (!any_percent_encoded_stuff) {
+    return gpr_slice_ref(slice_in);
+  }
+  p = GPR_SLICE_START_PTR(slice_in);
+  gpr_slice out = gpr_slice_malloc(out_length);
+  uint8_t *q = GPR_SLICE_START_PTR(out);
+  while (p != in_end) {
+    if (*p == '%') {
+      if (!valid_hex(p + 1, in_end) || !valid_hex(p + 2, in_end)) {
+        *q++ = *p++;
+      } else {
+        *q++ = (uint8_t)(dehex(p[1]) << 4) | (dehex(p[2]));
+        p += 3;
+      }
+    } else {
+      *q++ = *p++;
+    }
+  }
+  GPR_ASSERT(q == GPR_SLICE_END_PTR(out));
+  return out;
+}
diff --git a/src/core/lib/support/percent_encoding.h b/src/core/lib/support/percent_encoding.h
new file mode 100644
index 0000000000..000bf14ede
--- /dev/null
+++ b/src/core/lib/support/percent_encoding.h
@@ -0,0 +1,78 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_SUPPORT_PERCENT_ENCODING_H
+#define GRPC_CORE_LIB_SUPPORT_PERCENT_ENCODING_H
+
+/* Percent encoding and decoding of slices.
+   Transforms arbitrary strings into safe-for-transmission strings by using
+   variants of percent encoding (RFC 3986).
+   Two major variants are supplied: one that strictly matches URL encoding,
+     and another which applies percent encoding only to non-http2 header
+     bytes (the 'compatible' variant) */
+
+#include <stdbool.h>
+
+#include <grpc/support/slice.h>
+
+/* URL percent encoding spec bitfield (usabel as 'unreserved_bytes' in
+   gpr_percent_encode_slice, gpr_strict_percent_decode_slice).
+   Flags [A-Za-z0-9-_.~] as unreserved bytes for the percent encoding routines
+   */
+extern const uint8_t gpr_url_percent_encoding_unreserved_bytes[256 / 8];
+/* URL percent encoding spec bitfield (usabel as 'unreserved_bytes' in
+   gpr_percent_encode_slice, gpr_strict_percent_decode_slice).
+   Flags ascii7 non-control characters excluding '%' as unreserved bytes for the
+   percent encoding routines */
+extern const uint8_t gpr_compatible_percent_encoding_unreserved_bytes[256 / 8];
+
+/* Percent-encode a slice, returning the new slice (this cannot fail):
+   unreserved_bytes is a bitfield indicating which bytes are considered
+   unreserved and thus do not need percent encoding */
+gpr_slice gpr_percent_encode_slice(gpr_slice slice,
+                                   const uint8_t *unreserved_bytes);
+/* Percent-decode a slice, strictly.
+   If the input is legal (contains no unreserved bytes, and legal % encodings),
+   returns true and sets *slice_out to the decoded slice.
+   If the input is not legal, returns false and leaves *slice_out untouched.
+   unreserved_bytes is a bitfield indicating which bytes are considered
+   unreserved and thus do not need percent encoding */
+bool gpr_strict_percent_decode_slice(gpr_slice slice_in,
+                                     const uint8_t *unreserved_bytes,
+                                     gpr_slice *slice_out);
+/* Percent-decode a slice, permissively.
+   If a % triplet can not be decoded, pass it through verbatim.
+   This cannot fail. */
+gpr_slice gpr_permissive_percent_decode_slice(gpr_slice slice_in);
+
+#endif /* GRPC_CORE_LIB_SUPPORT_PERCENT_ENCODING_H */
diff --git a/src/core/lib/support/time_posix.c b/src/core/lib/support/time_posix.c
index 11542072fe..a69c501e9f 100644
--- a/src/core/lib/support/time_posix.c
+++ b/src/core/lib/support/time_posix.c
@@ -127,7 +127,7 @@ static gpr_timespec now_impl(gpr_clock_type clock) {
       now.tv_nsec = now_tv.tv_usec * 1000;
       break;
     case GPR_CLOCK_MONOTONIC:
-      now_dbl = (mach_absolute_time() - g_time_start) * g_time_scale;
+      now_dbl = ((double)(mach_absolute_time() - g_time_start)) * g_time_scale;
       now.tv_sec = (int64_t)(now_dbl * 1e-9);
       now.tv_nsec = (int32_t)(now_dbl - ((double)now.tv_sec) * 1e9);
       break;
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 772681109a..5690bcab1e 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -109,6 +109,10 @@ typedef struct batch_control {
   uint8_t recv_message;
   uint8_t recv_final_op;
   uint8_t is_notify_tag_closure;
+
+  /* TODO(ctiller): now that this is inlined, figure out how much of the above
+                    state can be eliminated */
+  grpc_transport_stream_op op;
 } batch_control;
 
 struct grpc_call {
@@ -122,8 +126,6 @@ struct grpc_call {
 
   /* client or server call */
   bool is_client;
-  /* is the alarm set */
-  bool have_alarm;
   /** has grpc_call_destroy been called */
   bool destroy_called;
   /** flag indicating that cancellation is inherited */
@@ -166,9 +168,6 @@ struct grpc_call {
   /* Contexts for various subsystems (security, tracing, ...). */
   grpc_call_context_element context[GRPC_CONTEXT_COUNT];
 
-  /* Deadline alarm - if have_alarm is non-zero */
-  grpc_timer alarm;
-
   /* for the client, extra metadata is initial metadata; for the
      server, it's trailing metadata */
   grpc_linked_mdelem send_extra_metadata[MAX_SEND_EXTRA_METADATA_COUNT];
@@ -211,8 +210,6 @@ struct grpc_call {
 #define CALL_FROM_TOP_ELEM(top_elem) \
   CALL_FROM_CALL_STACK(grpc_call_stack_from_top_element(top_elem))
 
-static void set_deadline_alarm(grpc_exec_ctx *exec_ctx, grpc_call *call,
-                               gpr_timespec deadline);
 static void execute_op(grpc_exec_ctx *exec_ctx, grpc_call *call,
                        grpc_transport_stream_op *op);
 static grpc_call_error cancel_with_status(grpc_exec_ctx *exec_ctx, grpc_call *c,
@@ -260,39 +257,8 @@ grpc_call *grpc_call_create(
       call->metadata_batch[i][j].deadline = gpr_inf_future(GPR_CLOCK_MONOTONIC);
     }
   }
-  call->send_deadline =
-      gpr_convert_clock_type(send_deadline, GPR_CLOCK_MONOTONIC);
-  GRPC_CHANNEL_INTERNAL_REF(channel, "call");
-  /* initial refcount dropped by grpc_call_destroy */
-  grpc_error *error = grpc_call_stack_init(
-      &exec_ctx, channel_stack, 1, destroy_call, call, call->context,
-      server_transport_data, CALL_STACK_FROM_CALL(call));
-  if (error != GRPC_ERROR_NONE) {
-    intptr_t status;
-    if (!grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, &status))
-      status = GRPC_STATUS_UNKNOWN;
-    const char *error_str =
-        grpc_error_get_str(error, GRPC_ERROR_STR_DESCRIPTION);
-    close_with_status(&exec_ctx, call, (grpc_status_code)status,
-                      error_str == NULL ? "unknown error" : error_str);
-    GRPC_ERROR_UNREF(error);
-  }
-  if (cq != NULL) {
-    GPR_ASSERT(
-        pollset_set_alternative == NULL &&
-        "Only one of 'cq' and 'pollset_set_alternative' should be non-NULL.");
-    GRPC_CQ_INTERNAL_REF(cq, "bind");
-    call->pollent =
-        grpc_polling_entity_create_from_pollset(grpc_cq_pollset(cq));
-  }
-  if (pollset_set_alternative != NULL) {
-    call->pollent =
-        grpc_polling_entity_create_from_pollset_set(pollset_set_alternative);
-  }
-  if (!grpc_polling_entity_is_empty(&call->pollent)) {
-    grpc_call_stack_set_pollset_or_pollset_set(
-        &exec_ctx, CALL_STACK_FROM_CALL(call), &call->pollent);
-  }
+  send_deadline = gpr_convert_clock_type(send_deadline, GPR_CLOCK_MONOTONIC);
+
   if (parent_call != NULL) {
     GRPC_CALL_INTERNAL_REF(parent_call, "child");
     GPR_ASSERT(call->is_client);
@@ -334,10 +300,38 @@ grpc_call *grpc_call_create(
 
     gpr_mu_unlock(&parent_call->mu);
   }
-  if (gpr_time_cmp(send_deadline, gpr_inf_future(send_deadline.clock_type)) !=
-      0) {
-    set_deadline_alarm(&exec_ctx, call, send_deadline);
+
+  call->send_deadline = send_deadline;
+
+  GRPC_CHANNEL_INTERNAL_REF(channel, "call");
+  /* initial refcount dropped by grpc_call_destroy */
+  grpc_error *error = grpc_call_stack_init(
+      &exec_ctx, channel_stack, 1, destroy_call, call, call->context,
+      server_transport_data, send_deadline, CALL_STACK_FROM_CALL(call));
+  if (error != GRPC_ERROR_NONE) {
+    grpc_status_code status;
+    const char *error_str;
+    grpc_error_get_status(error, &status, &error_str);
+    close_with_status(&exec_ctx, call, status, error_str);
+    GRPC_ERROR_UNREF(error);
   }
+  if (cq != NULL) {
+    GPR_ASSERT(
+        pollset_set_alternative == NULL &&
+        "Only one of 'cq' and 'pollset_set_alternative' should be non-NULL.");
+    GRPC_CQ_INTERNAL_REF(cq, "bind");
+    call->pollent =
+        grpc_polling_entity_create_from_pollset(grpc_cq_pollset(cq));
+  }
+  if (pollset_set_alternative != NULL) {
+    call->pollent =
+        grpc_polling_entity_create_from_pollset_set(pollset_set_alternative);
+  }
+  if (!grpc_polling_entity_is_empty(&call->pollent)) {
+    grpc_call_stack_set_pollset_or_pollset_set(
+        &exec_ctx, CALL_STACK_FROM_CALL(call), &call->pollent);
+  }
+
   grpc_exec_ctx_finish(&exec_ctx);
   GPR_TIMER_END("grpc_call_create", 0);
   return call;
@@ -450,20 +444,11 @@ static void set_status_details(grpc_call *call, status_source source,
 
 static void set_status_from_error(grpc_call *call, status_source source,
                                   grpc_error *error) {
-  intptr_t status;
-  if (grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, &status)) {
-    set_status_code(call, source, (uint32_t)status);
-  } else {
-    set_status_code(call, source, GRPC_STATUS_INTERNAL);
-  }
-  const char *msg = grpc_error_get_str(error, GRPC_ERROR_STR_GRPC_MESSAGE);
-  bool free_msg = false;
-  if (msg == NULL) {
-    free_msg = true;
-    msg = grpc_error_string(error);
-  }
+  grpc_status_code status;
+  const char *msg;
+  grpc_error_get_status(error, &status, &msg);
+  set_status_code(call, source, (uint32_t)status);
   set_status_details(call, source, grpc_mdstr_from_string(msg));
-  if (free_msg) grpc_error_free_string(msg);
 }
 
 static void set_incoming_compression_algorithm(
@@ -736,9 +721,6 @@ void grpc_call_destroy(grpc_call *c) {
   gpr_mu_lock(&c->mu);
   GPR_ASSERT(!c->destroy_called);
   c->destroy_called = 1;
-  if (c->have_alarm) {
-    grpc_timer_cancel(&exec_ctx, &c->alarm);
-  }
   cancel = !c->received_final_op;
   gpr_mu_unlock(&c->mu);
   if (cancel) grpc_call_cancel(c, NULL);
@@ -776,8 +758,8 @@ typedef struct termination_closure {
   grpc_closure closure;
   grpc_call *call;
   grpc_error *error;
-  grpc_closure *op_closure;
   enum { TC_CANCEL, TC_CLOSE } type;
+  grpc_transport_stream_op op;
 } termination_closure;
 
 static void done_termination(grpc_exec_ctx *exec_ctx, void *tcp,
@@ -792,31 +774,27 @@ static void done_termination(grpc_exec_ctx *exec_ctx, void *tcp,
       break;
   }
   GRPC_ERROR_UNREF(tc->error);
-  grpc_exec_ctx_sched(exec_ctx, tc->op_closure, GRPC_ERROR_NONE, NULL);
   gpr_free(tc);
 }
 
 static void send_cancel(grpc_exec_ctx *exec_ctx, void *tcp, grpc_error *error) {
-  grpc_transport_stream_op op;
   termination_closure *tc = tcp;
-  memset(&op, 0, sizeof(op));
-  op.cancel_error = tc->error;
+  memset(&tc->op, 0, sizeof(tc->op));
+  tc->op.cancel_error = tc->error;
   /* reuse closure to catch completion */
   grpc_closure_init(&tc->closure, done_termination, tc);
-  op.on_complete = &tc->closure;
-  execute_op(exec_ctx, tc->call, &op);
+  tc->op.on_complete = &tc->closure;
+  execute_op(exec_ctx, tc->call, &tc->op);
 }
 
 static void send_close(grpc_exec_ctx *exec_ctx, void *tcp, grpc_error *error) {
-  grpc_transport_stream_op op;
   termination_closure *tc = tcp;
-  memset(&op, 0, sizeof(op));
-  op.close_error = tc->error;
+  memset(&tc->op, 0, sizeof(tc->op));
+  tc->op.close_error = tc->error;
   /* reuse closure to catch completion */
   grpc_closure_init(&tc->closure, done_termination, tc);
-  tc->op_closure = op.on_complete;
-  op.on_complete = &tc->closure;
-  execute_op(exec_ctx, tc->call, &op);
+  tc->op.on_complete = &tc->closure;
+  execute_op(exec_ctx, tc->call, &tc->op);
 }
 
 static grpc_call_error terminate_with_status(grpc_exec_ctx *exec_ctx,
@@ -897,32 +875,6 @@ grpc_call *grpc_call_from_top_element(grpc_call_element *elem) {
   return CALL_FROM_TOP_ELEM(elem);
 }
 
-static void call_alarm(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
-  grpc_call *call = arg;
-  gpr_mu_lock(&call->mu);
-  call->have_alarm = 0;
-  if (error != GRPC_ERROR_CANCELLED) {
-    cancel_with_status(exec_ctx, call, GRPC_STATUS_DEADLINE_EXCEEDED,
-                       "Deadline Exceeded");
-  }
-  gpr_mu_unlock(&call->mu);
-  GRPC_CALL_INTERNAL_UNREF(exec_ctx, call, "alarm");
-}
-
-static void set_deadline_alarm(grpc_exec_ctx *exec_ctx, grpc_call *call,
-                               gpr_timespec deadline) {
-  if (call->have_alarm) {
-    gpr_log(GPR_ERROR, "Attempt to set deadline alarm twice");
-    assert(0);
-    return;
-  }
-  GRPC_CALL_INTERNAL_REF(call, "alarm");
-  call->have_alarm = 1;
-  call->send_deadline = gpr_convert_clock_type(deadline, GPR_CLOCK_MONOTONIC);
-  grpc_timer_init(exec_ctx, &call->alarm, call->send_deadline, call_alarm, call,
-                  gpr_now(GPR_CLOCK_MONOTONIC));
-}
-
 /* we offset status by a small amount when storing it into transport metadata
    as metadata cannot store a 0 value (which is used as OK for grpc_status_codes
    */
@@ -1160,17 +1112,6 @@ static void process_data_after_md(grpc_exec_ctx *exec_ctx, batch_control *bctl,
     if (gpr_unref(&bctl->steps_to_complete)) {
       post_batch_completion(exec_ctx, bctl);
     }
-  } else if (call->receiving_stream->length >
-             grpc_channel_get_max_message_length(call->channel)) {
-    cancel_with_status(exec_ctx, call, GRPC_STATUS_INTERNAL,
-                       "Max message size exceeded");
-    grpc_byte_stream_destroy(exec_ctx, call->receiving_stream);
-    call->receiving_stream = NULL;
-    *call->receiving_buffer = NULL;
-    call->receiving_message = 0;
-    if (gpr_unref(&bctl->steps_to_complete)) {
-      post_batch_completion(exec_ctx, bctl);
-    }
   } else {
     call->test_only_last_message_flags = call->receiving_stream->flags;
     if ((call->receiving_stream->flags & GRPC_WRITE_INTERNAL_COMPRESS) &&
@@ -1275,9 +1216,8 @@ static void receiving_initial_metadata_ready(grpc_exec_ctx *exec_ctx,
     if (gpr_time_cmp(md->deadline, gpr_inf_future(md->deadline.clock_type)) !=
             0 &&
         !call->is_client) {
-      GPR_TIMER_BEGIN("set_deadline_alarm", 0);
-      set_deadline_alarm(exec_ctx, call, md->deadline);
-      GPR_TIMER_END("set_deadline_alarm", 0);
+      call->send_deadline =
+          gpr_convert_clock_type(md->deadline, GPR_CLOCK_MONOTONIC);
     }
   }
 
@@ -1306,9 +1246,17 @@ static void finish_batch(grpc_exec_ctx *exec_ctx, void *bctlp,
   GRPC_ERROR_REF(error);
 
   gpr_mu_lock(&call->mu);
+
+  // If the error has an associated status code, set the call's status.
+  intptr_t status;
+  if (error != GRPC_ERROR_NONE &&
+      grpc_error_get_int(error, GRPC_ERROR_INT_GRPC_STATUS, &status)) {
+    set_status_from_error(call, STATUS_FROM_CORE, error);
+  }
+
   if (bctl->send_initial_metadata) {
     if (error != GRPC_ERROR_NONE) {
-      set_status_code(call, STATUS_FROM_CORE, GRPC_STATUS_UNAVAILABLE);
+      set_status_from_error(call, STATUS_FROM_CORE, error);
     }
     grpc_metadata_batch_destroy(
         &call->metadata_batch[0 /* is_receiving */][0 /* is_trailing */]);
@@ -1326,9 +1274,6 @@ static void finish_batch(grpc_exec_ctx *exec_ctx, void *bctlp,
     grpc_metadata_batch_filter(md, recv_trailing_filter, call);
 
     call->received_final_op = true;
-    if (call->have_alarm) {
-      grpc_timer_cancel(exec_ctx, &call->alarm);
-    }
     /* propagate cancellation to any interested children */
     child_call = call->first_child;
     if (child_call != NULL) {
@@ -1370,7 +1315,6 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
                                         grpc_call *call, const grpc_op *ops,
                                         size_t nops, void *notify_tag,
                                         int is_notify_tag_closure) {
-  grpc_transport_stream_op stream_op;
   size_t i;
   const grpc_op *op;
   batch_control *bctl;
@@ -1384,8 +1328,6 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
 
   GRPC_CALL_LOG_BATCH(GPR_INFO, call, ops, nops, notify_tag);
 
-  memset(&stream_op, 0, sizeof(stream_op));
-
   /* TODO(ctiller): this feels like it could be made lock-free */
   gpr_mu_lock(&call->mu);
   bctl = allocate_batch_control(call);
@@ -1394,6 +1336,9 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
   bctl->notify_tag = notify_tag;
   bctl->is_notify_tag_closure = (uint8_t)(is_notify_tag_closure != 0);
 
+  grpc_transport_stream_op *stream_op = &bctl->op;
+  memset(stream_op, 0, sizeof(*stream_op));
+
   if (nops == 0) {
     GRPC_CALL_INTERNAL_REF(call, "completion");
     bctl->error = GRPC_ERROR_NONE;
@@ -1471,9 +1416,9 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         }
         /* TODO(ctiller): just make these the same variable? */
         call->metadata_batch[0][0].deadline = call->send_deadline;
-        stream_op.send_initial_metadata =
+        stream_op->send_initial_metadata =
             &call->metadata_batch[0 /* is_receiving */][0 /* is_trailing */];
-        stream_op.send_initial_metadata_flags = op->flags;
+        stream_op->send_initial_metadata_flags = op->flags;
         break;
       case GRPC_OP_SEND_MESSAGE:
         if (!are_write_flags_valid(op->flags)) {
@@ -1493,7 +1438,7 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         grpc_slice_buffer_stream_init(
             &call->sending_stream,
             &op->data.send_message->data.raw.slice_buffer, op->flags);
-        stream_op.send_message = &call->sending_stream.base;
+        stream_op->send_message = &call->sending_stream.base;
         break;
       case GRPC_OP_SEND_CLOSE_FROM_CLIENT:
         /* Flag validation: currently allow no flags */
@@ -1511,7 +1456,7 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         }
         bctl->send_final_op = 1;
         call->sent_final_op = 1;
-        stream_op.send_trailing_metadata =
+        stream_op->send_trailing_metadata =
             &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
         break;
       case GRPC_OP_SEND_STATUS_FROM_SERVER:
@@ -1558,7 +1503,7 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
           error = GRPC_CALL_ERROR_INVALID_METADATA;
           goto done_with_error;
         }
-        stream_op.send_trailing_metadata =
+        stream_op->send_trailing_metadata =
             &call->metadata_batch[0 /* is_receiving */][1 /* is_trailing */];
         break;
       case GRPC_OP_RECV_INITIAL_METADATA:
@@ -1576,9 +1521,9 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         grpc_closure_init(&call->receiving_initial_metadata_ready,
                           receiving_initial_metadata_ready, bctl);
         bctl->recv_initial_metadata = 1;
-        stream_op.recv_initial_metadata =
+        stream_op->recv_initial_metadata =
             &call->metadata_batch[1 /* is_receiving */][0 /* is_trailing */];
-        stream_op.recv_initial_metadata_ready =
+        stream_op->recv_initial_metadata_ready =
             &call->receiving_initial_metadata_ready;
         num_completion_callbacks_needed++;
         break;
@@ -1595,10 +1540,10 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         call->receiving_message = 1;
         bctl->recv_message = 1;
         call->receiving_buffer = op->data.recv_message;
-        stream_op.recv_message = &call->receiving_stream;
+        stream_op->recv_message = &call->receiving_stream;
         grpc_closure_init(&call->receiving_stream_ready, receiving_stream_ready,
                           bctl);
-        stream_op.recv_message_ready = &call->receiving_stream_ready;
+        stream_op->recv_message_ready = &call->receiving_stream_ready;
         num_completion_callbacks_needed++;
         break;
       case GRPC_OP_RECV_STATUS_ON_CLIENT:
@@ -1624,9 +1569,9 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         call->final_op.client.status_details_capacity =
             op->data.recv_status_on_client.status_details_capacity;
         bctl->recv_final_op = 1;
-        stream_op.recv_trailing_metadata =
+        stream_op->recv_trailing_metadata =
             &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
-        stream_op.collect_stats =
+        stream_op->collect_stats =
             &call->final_info.stats.transport_stream_stats;
         break;
       case GRPC_OP_RECV_CLOSE_ON_SERVER:
@@ -1647,9 +1592,9 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
         call->final_op.server.cancelled =
             op->data.recv_close_on_server.cancelled;
         bctl->recv_final_op = 1;
-        stream_op.recv_trailing_metadata =
+        stream_op->recv_trailing_metadata =
             &call->metadata_batch[1 /* is_receiving */][1 /* is_trailing */];
-        stream_op.collect_stats =
+        stream_op->collect_stats =
             &call->final_info.stats.transport_stream_stats;
         break;
     }
@@ -1661,12 +1606,12 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
   }
   gpr_ref_init(&bctl->steps_to_complete, num_completion_callbacks_needed);
 
-  stream_op.context = call->context;
+  stream_op->context = call->context;
   grpc_closure_init(&bctl->finish_batch, finish_batch, bctl);
-  stream_op.on_complete = &bctl->finish_batch;
+  stream_op->on_complete = &bctl->finish_batch;
   gpr_mu_unlock(&call->mu);
 
-  execute_op(exec_ctx, call, &stream_op);
+  execute_op(exec_ctx, call, stream_op);
 
 done:
   GPR_TIMER_END("grpc_call_start_batch", 0);
diff --git a/src/core/lib/surface/channel.c b/src/core/lib/surface/channel.c
index 6d2b1c4935..6adb70a987 100644
--- a/src/core/lib/surface/channel.c
+++ b/src/core/lib/surface/channel.c
@@ -64,7 +64,6 @@ typedef struct registered_call {
 
 struct grpc_channel {
   int is_client;
-  uint32_t max_message_length;
   grpc_compression_options compression_options;
   grpc_mdelem *default_authority;
 
@@ -80,9 +79,6 @@ struct grpc_channel {
 #define CHANNEL_FROM_TOP_ELEM(top_elem) \
   CHANNEL_FROM_CHANNEL_STACK(grpc_channel_stack_from_top_element(top_elem))
 
-/* the protobuf library will (by default) start warning at 100megs */
-#define DEFAULT_MAX_MESSAGE_LENGTH (4 * 1024 * 1024)
-
 static void destroy_channel(grpc_exec_ctx *exec_ctx, void *arg,
                             grpc_error *error);
 
@@ -114,21 +110,10 @@ grpc_channel *grpc_channel_create(grpc_exec_ctx *exec_ctx, const char *target,
   gpr_mu_init(&channel->registered_call_mu);
   channel->registered_calls = NULL;
 
-  channel->max_message_length = DEFAULT_MAX_MESSAGE_LENGTH;
   grpc_compression_options_init(&channel->compression_options);
   if (args) {
     for (size_t i = 0; i < args->num_args; i++) {
-      if (0 == strcmp(args->args[i].key, GRPC_ARG_MAX_MESSAGE_LENGTH)) {
-        if (args->args[i].type != GRPC_ARG_INTEGER) {
-          gpr_log(GPR_ERROR, "%s ignored: it must be an integer",
-                  GRPC_ARG_MAX_MESSAGE_LENGTH);
-        } else if (args->args[i].value.integer < 0) {
-          gpr_log(GPR_ERROR, "%s ignored: it must be >= 0",
-                  GRPC_ARG_MAX_MESSAGE_LENGTH);
-        } else {
-          channel->max_message_length = (uint32_t)args->args[i].value.integer;
-        }
-      } else if (0 == strcmp(args->args[i].key, GRPC_ARG_DEFAULT_AUTHORITY)) {
+      if (0 == strcmp(args->args[i].key, GRPC_ARG_DEFAULT_AUTHORITY)) {
         if (args->args[i].type != GRPC_ARG_STRING) {
           gpr_log(GPR_ERROR, "%s ignored: it must be a string",
                   GRPC_ARG_DEFAULT_AUTHORITY);
@@ -334,14 +319,13 @@ static void destroy_channel(grpc_exec_ctx *exec_ctx, void *arg,
 }
 
 void grpc_channel_destroy(grpc_channel *channel) {
-  grpc_transport_op op;
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   grpc_channel_element *elem;
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GRPC_API_TRACE("grpc_channel_destroy(channel=%p)", 1, (channel));
-  memset(&op, 0, sizeof(op));
-  op.disconnect_with_error = GRPC_ERROR_CREATE("Channel Destroyed");
+  op->disconnect_with_error = GRPC_ERROR_CREATE("Channel Destroyed");
   elem = grpc_channel_stack_element(CHANNEL_STACK_FROM_CHANNEL(channel), 0);
-  elem->filter->start_transport_op(&exec_ctx, elem, &op);
+  elem->filter->start_transport_op(&exec_ctx, elem, op);
 
   GRPC_CHANNEL_INTERNAL_UNREF(&exec_ctx, channel, "channel");
 
@@ -371,7 +355,3 @@ grpc_mdelem *grpc_channel_get_reffed_status_elem(grpc_channel *channel, int i) {
   return grpc_mdelem_from_metadata_strings(GRPC_MDSTR_GRPC_STATUS,
                                            grpc_mdstr_from_string(tmp));
 }
-
-uint32_t grpc_channel_get_max_message_length(grpc_channel *channel) {
-  return channel->max_message_length;
-}
diff --git a/src/core/lib/surface/channel.h b/src/core/lib/surface/channel.h
index 4c62974346..23cc8656ca 100644
--- a/src/core/lib/surface/channel.h
+++ b/src/core/lib/surface/channel.h
@@ -64,7 +64,6 @@ grpc_channel_stack *grpc_channel_get_channel_stack(grpc_channel *channel);
     The returned elem is owned by the caller. */
 grpc_mdelem *grpc_channel_get_reffed_status_elem(grpc_channel *channel,
                                                  int status_code);
-uint32_t grpc_channel_get_max_message_length(grpc_channel *channel);
 
 #ifdef GRPC_STREAM_REFCOUNT_DEBUG
 void grpc_channel_internal_ref(grpc_channel *channel, const char *reason);
diff --git a/src/core/lib/surface/channel_ping.c b/src/core/lib/surface/channel_ping.c
index 9818f9d2f2..0d2f01a649 100644
--- a/src/core/lib/surface/channel_ping.c
+++ b/src/core/lib/surface/channel_ping.c
@@ -61,19 +61,20 @@ static void ping_done(grpc_exec_ctx *exec_ctx, void *arg, grpc_error *error) {
 
 void grpc_channel_ping(grpc_channel *channel, grpc_completion_queue *cq,
                        void *tag, void *reserved) {
-  grpc_transport_op op;
+  GRPC_API_TRACE("grpc_channel_ping(channel=%p, cq=%p, tag=%p, reserved=%p)", 4,
+                 (channel, cq, tag, reserved));
+  grpc_transport_op *op = grpc_make_transport_op(NULL);
   ping_result *pr = gpr_malloc(sizeof(*pr));
   grpc_channel_element *top_elem =
       grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
   grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   GPR_ASSERT(reserved == NULL);
-  memset(&op, 0, sizeof(op));
   pr->tag = tag;
   pr->cq = cq;
   grpc_closure_init(&pr->closure, ping_done, pr);
-  op.send_ping = &pr->closure;
-  op.bind_pollset = grpc_cq_pollset(cq);
+  op->send_ping = &pr->closure;
+  op->bind_pollset = grpc_cq_pollset(cq);
   grpc_cq_begin_op(cq, tag);
-  top_elem->filter->start_transport_op(&exec_ctx, top_elem, &op);
+  top_elem->filter->start_transport_op(&exec_ctx, top_elem, op);
   grpc_exec_ctx_finish(&exec_ctx);
 }
diff --git a/src/core/lib/surface/completion_queue.h b/src/core/lib/surface/completion_queue.h
index 3049284f68..4dbf3aae63 100644
--- a/src/core/lib/surface/completion_queue.h
+++ b/src/core/lib/surface/completion_queue.h
@@ -57,6 +57,8 @@ typedef struct grpc_cq_completion {
   uintptr_t next;
 } grpc_cq_completion;
 
+//#define GRPC_CQ_REF_COUNT_DEBUG
+
 #ifdef GRPC_CQ_REF_COUNT_DEBUG
 void grpc_cq_internal_ref(grpc_completion_queue *cc, const char *reason,
                           const char *file, int line);
diff --git a/src/core/lib/surface/init.c b/src/core/lib/surface/init.c
index 5397913a21..289f4ce8e8 100644
--- a/src/core/lib/surface/init.c
+++ b/src/core/lib/surface/init.c
@@ -43,10 +43,13 @@
 #include "src/core/lib/channel/channel_stack.h"
 #include "src/core/lib/channel/compress_filter.h"
 #include "src/core/lib/channel/connected_channel.h"
+#include "src/core/lib/channel/deadline_filter.h"
 #include "src/core/lib/channel/http_client_filter.h"
 #include "src/core/lib/channel/http_server_filter.h"
+#include "src/core/lib/channel/message_size_filter.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/http/parser.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/iomgr/iomgr.h"
 #include "src/core/lib/profiling/timers.h"
@@ -98,6 +101,21 @@ static bool maybe_add_http_filter(grpc_channel_stack_builder *builder,
 
 static void register_builtin_channel_init() {
   grpc_channel_init_register_stage(
+      GRPC_CLIENT_DIRECT_CHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY,
+      prepend_filter, (void *)&grpc_client_deadline_filter);
+  grpc_channel_init_register_stage(
+      GRPC_SERVER_CHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY, prepend_filter,
+      (void *)&grpc_server_deadline_filter);
+  grpc_channel_init_register_stage(
+      GRPC_CLIENT_SUBCHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY,
+      prepend_filter, (void *)&grpc_message_size_filter);
+  grpc_channel_init_register_stage(
+      GRPC_CLIENT_DIRECT_CHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY,
+      prepend_filter, (void *)&grpc_message_size_filter);
+  grpc_channel_init_register_stage(
+      GRPC_SERVER_CHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY, prepend_filter,
+      (void *)&grpc_message_size_filter);
+  grpc_channel_init_register_stage(
       GRPC_CLIENT_CHANNEL, GRPC_CHANNEL_INIT_BUILTIN_PRIORITY, prepend_filter,
       (void *)&grpc_compress_filter);
   grpc_channel_init_register_stage(
@@ -165,6 +183,7 @@ void grpc_init(void) {
     grpc_register_tracer("http1", &grpc_http1_trace);
     grpc_register_tracer("compression", &grpc_compression_trace);
     grpc_register_tracer("queue_pluck", &grpc_cq_pluck_trace);
+    grpc_register_tracer("combiner", &grpc_combiner_trace);
     // Default pluck trace to 1
     grpc_cq_pluck_trace = 1;
     grpc_register_tracer("queue_timeout", &grpc_cq_event_timeout_trace);
diff --git a/src/core/lib/surface/lame_client.c b/src/core/lib/surface/lame_client.c
index 19b78369dd..d32c884e8e 100644
--- a/src/core/lib/surface/lame_client.c
+++ b/src/core/lib/surface/lame_client.c
@@ -97,14 +97,14 @@ static void lame_start_transport_op(grpc_exec_ctx *exec_ctx,
     grpc_exec_ctx_sched(exec_ctx, op->on_connectivity_state_change,
                         GRPC_ERROR_NONE, NULL);
   }
-  if (op->on_consumed != NULL) {
-    grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
-  }
   if (op->send_ping != NULL) {
     grpc_exec_ctx_sched(exec_ctx, op->send_ping,
                         GRPC_ERROR_CREATE("lame client channel"), NULL);
   }
   GRPC_ERROR_UNREF(op->disconnect_with_error);
+  if (op->on_consumed != NULL) {
+    grpc_exec_ctx_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE, NULL);
+  }
 }
 
 static grpc_error *init_call_elem(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/surface/server.c b/src/core/lib/surface/server.c
index 55e6d99057..7300d79b9f 100644
--- a/src/core/lib/surface/server.c
+++ b/src/core/lib/surface/server.c
@@ -273,23 +273,20 @@ static void shutdown_cleanup(grpc_exec_ctx *exec_ctx, void *arg,
 }
 
 static void send_shutdown(grpc_exec_ctx *exec_ctx, grpc_channel *channel,
-                          bool send_goaway, grpc_error *send_disconnect) {
-  grpc_transport_op op;
-  struct shutdown_cleanup_args *sc;
+                          int send_goaway, grpc_error *send_disconnect) {
+  struct shutdown_cleanup_args *sc = gpr_malloc(sizeof(*sc));
+  grpc_closure_init(&sc->closure, shutdown_cleanup, sc);
+  grpc_transport_op *op = grpc_make_transport_op(&sc->closure);
   grpc_channel_element *elem;
 
-  memset(&op, 0, sizeof(op));
-  op.send_goaway = send_goaway;
-  sc = gpr_malloc(sizeof(*sc));
+  op->send_goaway = send_goaway;
   sc->slice = gpr_slice_from_copied_string("Server shutdown");
-  op.goaway_message = &sc->slice;
-  op.goaway_status = GRPC_STATUS_OK;
-  op.disconnect_with_error = send_disconnect;
-  grpc_closure_init(&sc->closure, shutdown_cleanup, sc);
-  op.on_consumed = &sc->closure;
+  op->goaway_message = &sc->slice;
+  op->goaway_status = GRPC_STATUS_OK;
+  op->disconnect_with_error = send_disconnect;
 
   elem = grpc_channel_stack_element(grpc_channel_get_channel_stack(channel), 0);
-  elem->filter->start_transport_op(exec_ctx, elem, &op);
+  elem->filter->start_transport_op(exec_ctx, elem, op);
 }
 
 static void channel_broadcaster_shutdown(grpc_exec_ctx *exec_ctx,
@@ -432,7 +429,8 @@ static void finish_destroy_channel(grpc_exec_ctx *exec_ctx, void *cd,
   server_unref(exec_ctx, server);
 }
 
-static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand) {
+static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand,
+                            grpc_error *error) {
   if (is_channel_orphaned(chand)) return;
   GPR_ASSERT(chand->server != NULL);
   orphan_channel(chand);
@@ -441,14 +439,20 @@ static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand) {
   chand->finish_destroy_channel_closure.cb = finish_destroy_channel;
   chand->finish_destroy_channel_closure.cb_arg = chand;
 
-  grpc_transport_op op;
-  memset(&op, 0, sizeof(op));
-  op.set_accept_stream = true;
-  op.on_consumed = &chand->finish_destroy_channel_closure;
+  grpc_transport_op *op =
+      grpc_make_transport_op(&chand->finish_destroy_channel_closure);
+  op->set_accept_stream = true;
   grpc_channel_next_op(exec_ctx,
                        grpc_channel_stack_element(
                            grpc_channel_get_channel_stack(chand->channel), 0),
-                       &op);
+                       op);
+
+  if (error != GRPC_ERROR_NONE) {
+    const char *msg = grpc_error_string(error);
+    gpr_log(GPR_INFO, "Disconnected client: %s", msg);
+    grpc_error_free_string(msg);
+  }
+  GRPC_ERROR_UNREF(error);
 }
 
 static void cpstr(char **dest, size_t *capacity, grpc_mdstr *value) {
@@ -845,17 +849,16 @@ static void channel_connectivity_changed(grpc_exec_ctx *exec_ctx, void *cd,
   channel_data *chand = cd;
   grpc_server *server = chand->server;
   if (chand->connectivity_state != GRPC_CHANNEL_SHUTDOWN) {
-    grpc_transport_op op;
-    memset(&op, 0, sizeof(op));
-    op.on_connectivity_state_change = &chand->channel_connectivity_changed,
-    op.connectivity_state = &chand->connectivity_state;
+    grpc_transport_op *op = grpc_make_transport_op(NULL);
+    op->on_connectivity_state_change = &chand->channel_connectivity_changed,
+    op->connectivity_state = &chand->connectivity_state;
     grpc_channel_next_op(exec_ctx,
                          grpc_channel_stack_element(
                              grpc_channel_get_channel_stack(chand->channel), 0),
-                         &op);
+                         op);
   } else {
     gpr_mu_lock(&server->mu_global);
-    destroy_channel(exec_ctx, chand);
+    destroy_channel(exec_ctx, chand, GRPC_ERROR_REF(error));
     gpr_mu_unlock(&server->mu_global);
     GRPC_CHANNEL_INTERNAL_UNREF(exec_ctx, chand->channel, "connectivity");
   }
@@ -1103,6 +1106,12 @@ void grpc_server_start(grpc_server *server) {
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
+void grpc_server_get_pollsets(grpc_server *server, grpc_pollset ***pollsets,
+                              size_t *pollset_count) {
+  *pollset_count = server->cq_count;
+  *pollsets = server->pollsets;
+}
+
 void grpc_server_setup_transport(grpc_exec_ctx *exec_ctx, grpc_server *s,
                                  grpc_transport *transport,
                                  grpc_pollset *accepting_pollset,
@@ -1119,7 +1128,7 @@ void grpc_server_setup_transport(grpc_exec_ctx *exec_ctx, grpc_server *s,
   size_t slots;
   uint32_t probes;
   uint32_t max_probes = 0;
-  grpc_transport_op op;
+  grpc_transport_op *op = NULL;
 
   channel =
       grpc_channel_create(exec_ctx, NULL, args, GRPC_SERVER_CHANNEL, transport);
@@ -1179,16 +1188,16 @@ void grpc_server_setup_transport(grpc_exec_ctx *exec_ctx, grpc_server *s,
   gpr_mu_unlock(&s->mu_global);
 
   GRPC_CHANNEL_INTERNAL_REF(channel, "connectivity");
-  memset(&op, 0, sizeof(op));
-  op.set_accept_stream = true;
-  op.set_accept_stream_fn = accept_stream;
-  op.set_accept_stream_user_data = chand;
-  op.on_connectivity_state_change = &chand->channel_connectivity_changed;
-  op.connectivity_state = &chand->connectivity_state;
+  op = grpc_make_transport_op(NULL);
+  op->set_accept_stream = true;
+  op->set_accept_stream_fn = accept_stream;
+  op->set_accept_stream_user_data = chand;
+  op->on_connectivity_state_change = &chand->channel_connectivity_changed;
+  op->connectivity_state = &chand->connectivity_state;
   if (gpr_atm_acq_load(&s->shutdown_flag) != 0) {
-    op.disconnect_with_error = GRPC_ERROR_CREATE("Server shutdown");
+    op->disconnect_with_error = GRPC_ERROR_CREATE("Server shutdown");
   }
-  grpc_transport_perform_op(exec_ctx, transport, &op);
+  grpc_transport_perform_op(exec_ctx, transport, op);
 }
 
 void done_published_shutdown(grpc_exec_ctx *exec_ctx, void *done_arg,
diff --git a/src/core/lib/surface/server.h b/src/core/lib/surface/server.h
index fb6e4d60c5..551a40a4ff 100644
--- a/src/core/lib/surface/server.h
+++ b/src/core/lib/surface/server.h
@@ -60,4 +60,9 @@ const grpc_channel_args *grpc_server_get_channel_args(grpc_server *server);
 
 int grpc_server_has_open_connections(grpc_server *server);
 
+/* Do not call this before grpc_server_start. Returns the pollsets and the
+ * number of pollsets via 'pollsets' and 'pollset_count'. */
+void grpc_server_get_pollsets(grpc_server *server, grpc_pollset ***pollsets,
+                              size_t *pollset_count);
+
 #endif /* GRPC_CORE_LIB_SURFACE_SERVER_H */
diff --git a/src/core/lib/transport/metadata.c b/src/core/lib/transport/metadata.c
index 0677f29766..4b40c275ad 100644
--- a/src/core/lib/transport/metadata.c
+++ b/src/core/lib/transport/metadata.c
@@ -278,7 +278,7 @@ static void ref_md_locked(mdtab_shard *shard,
                           internal_metadata *md DEBUG_ARGS) {
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM   REF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM   REF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) + 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
@@ -566,7 +566,7 @@ grpc_mdelem *grpc_mdelem_from_metadata_strings(grpc_mdstr *mkey,
   shard->elems[idx] = md;
   gpr_mu_init(&md->mu_user_data);
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
-  gpr_log(GPR_DEBUG, "ELM   NEW:%p:%d: '%s' = '%s'", md,
+  gpr_log(GPR_DEBUG, "ELM   NEW:%p:%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->value));
@@ -639,7 +639,7 @@ grpc_mdelem *grpc_mdelem_ref(grpc_mdelem *gmd DEBUG_ARGS) {
   if (is_mdelem_static(gmd)) return gmd;
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM   REF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM   REF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) + 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
@@ -649,7 +649,7 @@ grpc_mdelem *grpc_mdelem_ref(grpc_mdelem *gmd DEBUG_ARGS) {
      this function - meaning that no adjustment to mdtab_free is necessary,
      simplifying the logic here to be just an atomic increment */
   /* use C assert to have this removed in opt builds */
-  assert(gpr_atm_no_barrier_load(&md->refcnt) >= 1);
+  GPR_ASSERT(gpr_atm_no_barrier_load(&md->refcnt) >= 1);
   gpr_atm_no_barrier_fetch_add(&md->refcnt, 1);
   return gmd;
 }
@@ -660,14 +660,16 @@ void grpc_mdelem_unref(grpc_mdelem *gmd DEBUG_ARGS) {
   if (is_mdelem_static(gmd)) return;
 #ifdef GRPC_METADATA_REFCOUNT_DEBUG
   gpr_log(file, line, GPR_LOG_SEVERITY_DEBUG,
-          "ELM UNREF:%p:%d->%d: '%s' = '%s'", md,
+          "ELM UNREF:%p:%zu->%zu: '%s' = '%s'", (void *)md,
           gpr_atm_no_barrier_load(&md->refcnt),
           gpr_atm_no_barrier_load(&md->refcnt) - 1,
           grpc_mdstr_as_c_string((grpc_mdstr *)md->key),
           grpc_mdstr_as_c_string((grpc_mdstr *)md->value));
 #endif
   uint32_t hash = GRPC_MDSTR_KV_HASH(md->key->hash, md->value->hash);
-  if (1 == gpr_atm_full_fetch_add(&md->refcnt, -1)) {
+  const gpr_atm prev_refcount = gpr_atm_full_fetch_add(&md->refcnt, -1);
+  GPR_ASSERT(prev_refcount >= 1);
+  if (1 == prev_refcount) {
     /* once the refcount hits zero, some other thread can come along and
        free md at any time: it's unsafe from this point on to access it */
     mdtab_shard *shard =
@@ -676,10 +678,12 @@ void grpc_mdelem_unref(grpc_mdelem *gmd DEBUG_ARGS) {
   }
 }
 
-const char *grpc_mdstr_as_c_string(grpc_mdstr *s) {
+const char *grpc_mdstr_as_c_string(const grpc_mdstr *s) {
   return (const char *)GPR_SLICE_START_PTR(s->slice);
 }
 
+size_t grpc_mdstr_length(const grpc_mdstr *s) { return GRPC_MDSTR_LENGTH(s); }
+
 grpc_mdstr *grpc_mdstr_ref(grpc_mdstr *gs DEBUG_ARGS) {
   internal_string *s = (internal_string *)gs;
   if (is_mdstr_static(gs)) return gs;
diff --git a/src/core/lib/transport/metadata.h b/src/core/lib/transport/metadata.h
index 2b0921c8d7..71eff0acf2 100644
--- a/src/core/lib/transport/metadata.h
+++ b/src/core/lib/transport/metadata.h
@@ -147,7 +147,7 @@ void grpc_mdelem_unref(grpc_mdelem *md);
 
 /* Recover a char* from a grpc_mdstr. The returned string is null terminated.
    Does not promise that the returned string has no embedded nulls however. */
-const char *grpc_mdstr_as_c_string(grpc_mdstr *s);
+const char *grpc_mdstr_as_c_string(const grpc_mdstr *s);
 
 #define GRPC_MDSTR_LENGTH(s) (GPR_SLICE_LENGTH(s->slice))
 
diff --git a/src/core/lib/transport/static_metadata.c b/src/core/lib/transport/static_metadata.c
index fce591f346..5e0352a467 100644
--- a/src/core/lib/transport/static_metadata.c
+++ b/src/core/lib/transport/static_metadata.c
@@ -54,7 +54,7 @@ const uint8_t grpc_static_metadata_elem_indices[GRPC_STATIC_MDELEM_COUNT * 2] =
     {11, 33, 10, 33, 12, 33, 12, 50, 13, 33, 14, 33, 15, 33, 16, 33, 17, 33,
      19, 33, 20, 33, 21, 33, 22, 33, 23, 33, 24, 33, 25, 33, 26, 33, 27, 33,
      28, 18, 28, 33, 29, 33, 30, 33, 34, 33, 35, 33, 36, 33, 37, 33, 40, 31,
-     40, 32, 40, 49, 40, 54, 40, 55, 40, 56, 40, 57, 42, 31, 42, 49, 42, 54,
+     40, 32, 40, 49, 40, 54, 40, 55, 40, 56, 40, 57, 41, 31, 41, 49, 41, 54,
      46, 0,  46, 1,  46, 2,  51, 33, 58, 33, 59, 33, 60, 33, 61, 33, 62, 33,
      63, 33, 64, 33, 65, 33, 66, 33, 67, 33, 68, 33, 69, 38, 69, 71, 69, 74,
      70, 82, 70, 83, 72, 33, 73, 33, 75, 33, 76, 33, 77, 33, 78, 33, 79, 39,
@@ -103,11 +103,11 @@ const char *const grpc_static_metadata_strings[GRPC_STATIC_MDSTR_COUNT] = {
     "GET",
     "grpc",
     "grpc-accept-encoding",
-    "grpc-census-bin",
     "grpc-encoding",
     "grpc-internal-encoding-request",
     "grpc-message",
     "grpc-payload-bin",
+    "grpc-stats-bin",
     "grpc-status",
     "grpc-timeout",
     "grpc-tracing-bin",
diff --git a/src/core/lib/transport/static_metadata.h b/src/core/lib/transport/static_metadata.h
index 54b6f38be1..5b9ee1a60a 100644
--- a/src/core/lib/transport/static_metadata.h
+++ b/src/core/lib/transport/static_metadata.h
@@ -128,16 +128,16 @@ extern grpc_mdstr grpc_static_mdstr_table[GRPC_STATIC_MDSTR_COUNT];
 #define GRPC_MDSTR_GRPC (&grpc_static_mdstr_table[39])
 /* "grpc-accept-encoding" */
 #define GRPC_MDSTR_GRPC_ACCEPT_ENCODING (&grpc_static_mdstr_table[40])
-/* "grpc-census-bin" */
-#define GRPC_MDSTR_GRPC_CENSUS_BIN (&grpc_static_mdstr_table[41])
 /* "grpc-encoding" */
-#define GRPC_MDSTR_GRPC_ENCODING (&grpc_static_mdstr_table[42])
+#define GRPC_MDSTR_GRPC_ENCODING (&grpc_static_mdstr_table[41])
 /* "grpc-internal-encoding-request" */
-#define GRPC_MDSTR_GRPC_INTERNAL_ENCODING_REQUEST (&grpc_static_mdstr_table[43])
+#define GRPC_MDSTR_GRPC_INTERNAL_ENCODING_REQUEST (&grpc_static_mdstr_table[42])
 /* "grpc-message" */
-#define GRPC_MDSTR_GRPC_MESSAGE (&grpc_static_mdstr_table[44])
+#define GRPC_MDSTR_GRPC_MESSAGE (&grpc_static_mdstr_table[43])
 /* "grpc-payload-bin" */
-#define GRPC_MDSTR_GRPC_PAYLOAD_BIN (&grpc_static_mdstr_table[45])
+#define GRPC_MDSTR_GRPC_PAYLOAD_BIN (&grpc_static_mdstr_table[44])
+/* "grpc-stats-bin" */
+#define GRPC_MDSTR_GRPC_STATS_BIN (&grpc_static_mdstr_table[45])
 /* "grpc-status" */
 #define GRPC_MDSTR_GRPC_STATUS (&grpc_static_mdstr_table[46])
 /* "grpc-timeout" */
diff --git a/src/core/lib/transport/transport.c b/src/core/lib/transport/transport.c
index 857c3909d2..82fc605218 100644
--- a/src/core/lib/transport/transport.c
+++ b/src/core/lib/transport/transport.c
@@ -32,10 +32,14 @@
  */
 
 #include "src/core/lib/transport/transport.h"
+
+#include <string.h>
+
 #include <grpc/support/alloc.h>
 #include <grpc/support/atm.h>
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
+
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/transport/transport_impl.h"
 
@@ -43,7 +47,7 @@
 void grpc_stream_ref(grpc_stream_refcount *refcount, const char *reason) {
   gpr_atm val = gpr_atm_no_barrier_load(&refcount->refs.count);
   gpr_log(GPR_DEBUG, "%s %p:%p   REF %d->%d %s", refcount->object_type,
-          refcount, refcount->destroy.cb_arg, val, val + 1, reason);
+          refcount, refcount->destroy.cb_arg, (int)val, (int)val + 1, reason);
 #else
 void grpc_stream_ref(grpc_stream_refcount *refcount) {
 #endif
@@ -55,7 +59,7 @@ void grpc_stream_unref(grpc_exec_ctx *exec_ctx, grpc_stream_refcount *refcount,
                        const char *reason) {
   gpr_atm val = gpr_atm_no_barrier_load(&refcount->refs.count);
   gpr_log(GPR_DEBUG, "%s %p:%p UNREF %d->%d %s", refcount->object_type,
-          refcount, refcount->destroy.cb_arg, val, val - 1, reason);
+          refcount, refcount->destroy.cb_arg, (int)val, (int)val - 1, reason);
 #else
 void grpc_stream_unref(grpc_exec_ctx *exec_ctx,
                        grpc_stream_refcount *refcount) {
@@ -220,7 +224,7 @@ void grpc_transport_stream_op_add_cancellation_with_message(
     error = GRPC_ERROR_CREATE("Call cancelled");
   }
   error = grpc_error_set_int(error, GRPC_ERROR_INT_GRPC_STATUS, status);
-  add_error(op, &op->close_error, error);
+  add_error(op, &op->cancel_error, error);
 }
 
 void grpc_transport_stream_op_add_close(grpc_transport_stream_op *op,
@@ -247,3 +251,26 @@ void grpc_transport_stream_op_add_close(grpc_transport_stream_op *op,
   error = grpc_error_set_int(error, GRPC_ERROR_INT_GRPC_STATUS, status);
   add_error(op, &op->close_error, error);
 }
+
+typedef struct {
+  grpc_closure outer_on_complete;
+  grpc_closure *inner_on_complete;
+  grpc_transport_op op;
+} made_transport_op;
+
+static void destroy_made_transport_op(grpc_exec_ctx *exec_ctx, void *arg,
+                                      grpc_error *error) {
+  made_transport_op *op = arg;
+  grpc_exec_ctx_sched(exec_ctx, op->inner_on_complete, GRPC_ERROR_REF(error),
+                      NULL);
+  gpr_free(op);
+}
+
+grpc_transport_op *grpc_make_transport_op(grpc_closure *on_complete) {
+  made_transport_op *op = gpr_malloc(sizeof(*op));
+  grpc_closure_init(&op->outer_on_complete, destroy_made_transport_op, op);
+  op->inner_on_complete = on_complete;
+  memset(&op->op, 0, sizeof(op->op));
+  op->op.on_consumed = &op->outer_on_complete;
+  return &op->op;
+}
diff --git a/src/core/lib/transport/transport.h b/src/core/lib/transport/transport.h
index 26ed6cb839..8dc393fd61 100644
--- a/src/core/lib/transport/transport.h
+++ b/src/core/lib/transport/transport.h
@@ -100,6 +100,11 @@ void grpc_transport_move_one_way_stats(grpc_transport_one_way_stats *from,
 void grpc_transport_move_stats(grpc_transport_stream_stats *from,
                                grpc_transport_stream_stats *to);
 
+typedef struct {
+  grpc_closure closure;
+  void *args[2];
+} grpc_transport_private_op_data;
+
 /* Transport stream op: a set of operations to perform on a transport
    against a single stream */
 typedef struct grpc_transport_stream_op {
@@ -149,6 +154,12 @@ typedef struct grpc_transport_stream_op {
 
   /* Indexes correspond to grpc_context_index enum values */
   grpc_call_context_element *context;
+
+  /***************************************************************************
+   * remaining fields are initialized and used at the discretion of the
+   * transport implementation */
+
+  grpc_transport_private_op_data transport_private;
 } grpc_transport_stream_op;
 
 /** Transport op: a set of operations to perform on a transport as a whole */
@@ -182,6 +193,12 @@ typedef struct grpc_transport_op {
   grpc_pollset_set *bind_pollset_set;
   /** send a ping, call this back if not NULL */
   grpc_closure *send_ping;
+
+  /***************************************************************************
+   * remaining fields are initialized and used at the discretion of the
+   * transport implementation */
+
+  grpc_transport_private_op_data transport_private;
 } grpc_transport_op;
 
 /* Returns the amount of memory required to store a grpc_stream for this
@@ -273,6 +290,10 @@ void grpc_transport_destroy(grpc_exec_ctx *exec_ctx, grpc_transport *transport);
 char *grpc_transport_get_peer(grpc_exec_ctx *exec_ctx,
                               grpc_transport *transport);
 
+/* Allocate a grpc_transport_op, and preconfigure the on_consumed closure to
+   \a on_consumed and then delete the returned transport op */
+grpc_transport_op *grpc_make_transport_op(grpc_closure *on_consumed);
+
 #ifdef __cplusplus
 }
 #endif