Merge pull request #9660 from ctiller/c3

Convert client_channel.c to use a combiner lock

24 files changed, 419 insertions, 295 deletions

diff --git a/src/core/ext/client_channel/client_channel.c b/src/core/ext/client_channel/client_channel.c
index 06038bb5ba..62fb061bcf 100644
--- a/src/core/ext/client_channel/client_channel.c
+++ b/src/core/ext/client_channel/client_channel.c
@@ -51,6 +51,7 @@
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/connected_channel.h"
 #include "src/core/lib/channel/deadline_filter.h"
+#include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/iomgr/iomgr.h"
 #include "src/core/lib/iomgr/polling_entity.h"
 #include "src/core/lib/profiling/timers.h"
@@ -160,13 +161,10 @@ typedef struct client_channel_channel_data {
   /** client channel factory */
   grpc_client_channel_factory *client_channel_factory;
 
-  /** mutex protecting all variables below in this data structure */
-  gpr_mu mu;
+  /** combiner protecting all variables below in this data structure */
+  grpc_combiner *combiner;
   /** currently active load balancer */
-  char *lb_policy_name;
   grpc_lb_policy *lb_policy;
-  /** service config in JSON form */
-  char *service_config_json;
   /** maps method names to method_parameters structs */
   grpc_slice_hash_table *method_params_table;
   /** incoming resolver result - set by resolver.next() */
@@ -183,6 +181,13 @@ typedef struct client_channel_channel_data {
   grpc_channel_stack *owning_stack;
   /** interested parties (owned) */
   grpc_pollset_set *interested_parties;
+
+  /* the following properties are guarded by a mutex since API's require them
+     to be instantaniously available */
+  gpr_mu info_mu;
+  char *info_lb_policy_name;
+  /** service config in JSON form */
+  char *info_service_config_json;
 } channel_data;
 
 /** We create one watcher for each new lb_policy that is returned from a
@@ -218,32 +223,23 @@ static void set_channel_connectivity_state_locked(grpc_exec_ctx *exec_ctx,
 }
 
 static void on_lb_policy_state_changed_locked(grpc_exec_ctx *exec_ctx,
-                                              lb_policy_connectivity_watcher *w,
-                                              grpc_error *error) {
+                                              void *arg, grpc_error *error) {
+  lb_policy_connectivity_watcher *w = arg;
   grpc_connectivity_state publish_state = w->state;
-  /* check if the notification is for a stale policy */
-  if (w->lb_policy != w->chand->lb_policy) return;
-
-  if (publish_state == GRPC_CHANNEL_SHUTDOWN && w->chand->resolver != NULL) {
-    publish_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
-    grpc_resolver_channel_saw_error(exec_ctx, w->chand->resolver);
-    GRPC_LB_POLICY_UNREF(exec_ctx, w->chand->lb_policy, "channel");
-    w->chand->lb_policy = NULL;
-  }
-  set_channel_connectivity_state_locked(exec_ctx, w->chand, publish_state,
-                                        GRPC_ERROR_REF(error), "lb_changed");
-  if (w->state != GRPC_CHANNEL_SHUTDOWN) {
-    watch_lb_policy(exec_ctx, w->chand, w->lb_policy, w->state);
+  /* check if the notification is for the latest policy */
+  if (w->lb_policy == w->chand->lb_policy) {
+    if (publish_state == GRPC_CHANNEL_SHUTDOWN && w->chand->resolver != NULL) {
+      publish_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
+      grpc_resolver_channel_saw_error(exec_ctx, w->chand->resolver);
+      GRPC_LB_POLICY_UNREF(exec_ctx, w->chand->lb_policy, "channel");
+      w->chand->lb_policy = NULL;
+    }
+    set_channel_connectivity_state_locked(exec_ctx, w->chand, publish_state,
+                                          GRPC_ERROR_REF(error), "lb_changed");
+    if (w->state != GRPC_CHANNEL_SHUTDOWN) {
+      watch_lb_policy(exec_ctx, w->chand, w->lb_policy, w->state);
+    }
   }
-}
-
-static void on_lb_policy_state_changed(grpc_exec_ctx *exec_ctx, void *arg,
-                                       grpc_error *error) {
-  lb_policy_connectivity_watcher *w = arg;
-
-  gpr_mu_lock(&w->chand->mu);
-  on_lb_policy_state_changed_locked(exec_ctx, w, error);
-  gpr_mu_unlock(&w->chand->mu);
 
   GRPC_CHANNEL_STACK_UNREF(exec_ctx, w->chand->owning_stack, "watch_lb_policy");
   gpr_free(w);
@@ -256,16 +252,16 @@ static void watch_lb_policy(grpc_exec_ctx *exec_ctx, channel_data *chand,
   GRPC_CHANNEL_STACK_REF(chand->owning_stack, "watch_lb_policy");
 
   w->chand = chand;
-  grpc_closure_init(&w->on_changed, on_lb_policy_state_changed, w,
-                    grpc_schedule_on_exec_ctx);
+  grpc_closure_init(&w->on_changed, on_lb_policy_state_changed_locked, w,
+                    grpc_combiner_scheduler(chand->combiner, false));
   w->state = current_state;
   w->lb_policy = lb_policy;
   grpc_lb_policy_notify_on_state_change(exec_ctx, lb_policy, &w->state,
                                         &w->on_changed);
 }
 
-static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
-                                       grpc_error *error) {
+static void on_resolver_result_changed_locked(grpc_exec_ctx *exec_ctx,
+                                              void *arg, grpc_error *error) {
   channel_data *chand = arg;
   char *lb_policy_name = NULL;
   grpc_lb_policy *lb_policy = NULL;
@@ -353,17 +349,18 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
                                      chand->interested_parties);
   }
 
-  gpr_mu_lock(&chand->mu);
+  gpr_mu_lock(&chand->info_mu);
   if (lb_policy_name != NULL) {
-    gpr_free(chand->lb_policy_name);
-    chand->lb_policy_name = lb_policy_name;
+    gpr_free(chand->info_lb_policy_name);
+    chand->info_lb_policy_name = lb_policy_name;
   }
   old_lb_policy = chand->lb_policy;
   chand->lb_policy = lb_policy;
   if (service_config_json != NULL) {
-    gpr_free(chand->service_config_json);
-    chand->service_config_json = service_config_json;
+    gpr_free(chand->info_service_config_json);
+    chand->info_service_config_json = service_config_json;
   }
+  gpr_mu_unlock(&chand->info_mu);
   if (chand->method_params_table != NULL) {
     grpc_slice_hash_table_unref(exec_ctx, chand->method_params_table);
   }
@@ -391,7 +388,6 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
     GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
     grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
                        &chand->on_resolver_result_changed);
-    gpr_mu_unlock(&chand->mu);
   } else {
     if (chand->resolver != NULL) {
       grpc_resolver_shutdown(exec_ctx, chand->resolver);
@@ -404,7 +400,6 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
         GRPC_ERROR_CREATE_REFERENCING("Got config after disconnection", refs,
                                       GPR_ARRAY_SIZE(refs)),
         "resolver_gone");
-    gpr_mu_unlock(&chand->mu);
   }
 
   if (exit_idle) {
@@ -426,20 +421,12 @@ static void on_resolver_result_changed(grpc_exec_ctx *exec_ctx, void *arg,
   GRPC_ERROR_UNREF(state_error);
 }
 
-static void cc_start_transport_op(grpc_exec_ctx *exec_ctx,
-                                  grpc_channel_element *elem,
-                                  grpc_transport_op *op) {
+static void start_transport_op_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                      grpc_error *error_ignored) {
+  grpc_transport_op *op = arg;
+  grpc_channel_element *elem = op->transport_private.args[0];
   channel_data *chand = elem->channel_data;
 
-  grpc_closure_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE);
-
-  GPR_ASSERT(op->set_accept_stream == false);
-  if (op->bind_pollset != NULL) {
-    grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties,
-                                 op->bind_pollset);
-  }
-
-  gpr_mu_lock(&chand->mu);
   if (op->on_connectivity_state_change != NULL) {
     grpc_connectivity_state_notify_on_state_change(
         exec_ctx, &chand->state_tracker, op->connectivity_state,
@@ -482,25 +469,48 @@ static void cc_start_transport_op(grpc_exec_ctx *exec_ctx,
     }
     GRPC_ERROR_UNREF(op->disconnect_with_error);
   }
-  gpr_mu_unlock(&chand->mu);
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "start_transport_op");
+
+  grpc_closure_sched(exec_ctx, op->on_consumed, GRPC_ERROR_NONE);
+}
+
+static void cc_start_transport_op(grpc_exec_ctx *exec_ctx,
+                                  grpc_channel_element *elem,
+                                  grpc_transport_op *op) {
+  channel_data *chand = elem->channel_data;
+
+  GPR_ASSERT(op->set_accept_stream == false);
+  if (op->bind_pollset != NULL) {
+    grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties,
+                                 op->bind_pollset);
+  }
+
+  op->transport_private.args[0] = elem;
+  GRPC_CHANNEL_STACK_REF(chand->owning_stack, "start_transport_op");
+  grpc_closure_sched(
+      exec_ctx, grpc_closure_init(
+                    &op->transport_private.closure, start_transport_op_locked,
+                    op, grpc_combiner_scheduler(chand->combiner, false)),
+      GRPC_ERROR_NONE);
 }
 
 static void cc_get_channel_info(grpc_exec_ctx *exec_ctx,
                                 grpc_channel_element *elem,
                                 const grpc_channel_info *info) {
   channel_data *chand = elem->channel_data;
-  gpr_mu_lock(&chand->mu);
+  gpr_mu_lock(&chand->info_mu);
   if (info->lb_policy_name != NULL) {
-    *info->lb_policy_name = chand->lb_policy_name == NULL
+    *info->lb_policy_name = chand->info_lb_policy_name == NULL
                                 ? NULL
-                                : gpr_strdup(chand->lb_policy_name);
+                                : gpr_strdup(chand->info_lb_policy_name);
   }
   if (info->service_config_json != NULL) {
-    *info->service_config_json = chand->service_config_json == NULL
-                                     ? NULL
-                                     : gpr_strdup(chand->service_config_json);
+    *info->service_config_json =
+        chand->info_service_config_json == NULL
+            ? NULL
+            : gpr_strdup(chand->info_service_config_json);
   }
-  gpr_mu_unlock(&chand->mu);
+  gpr_mu_unlock(&chand->info_mu);
 }
 
 /* Constructor for channel_data */
@@ -512,11 +522,12 @@ static grpc_error *cc_init_channel_elem(grpc_exec_ctx *exec_ctx,
   GPR_ASSERT(args->is_last);
   GPR_ASSERT(elem->filter == &grpc_client_channel_filter);
   // Initialize data members.
-  gpr_mu_init(&chand->mu);
+  chand->combiner = grpc_combiner_create(NULL);
+  gpr_mu_init(&chand->info_mu);
   chand->owning_stack = args->channel_stack;
   grpc_closure_init(&chand->on_resolver_result_changed,
-                    on_resolver_result_changed, chand,
-                    grpc_schedule_on_exec_ctx);
+                    on_resolver_result_changed_locked, chand,
+                    grpc_combiner_scheduler(chand->combiner, false));
   chand->interested_parties = grpc_pollset_set_create();
   grpc_connectivity_state_init(&chand->state_tracker, GRPC_CHANNEL_IDLE,
                                "client_channel");
@@ -565,14 +576,15 @@ static void cc_destroy_channel_elem(grpc_exec_ctx *exec_ctx,
                                      chand->interested_parties);
     GRPC_LB_POLICY_UNREF(exec_ctx, chand->lb_policy, "channel");
   }
-  gpr_free(chand->lb_policy_name);
-  gpr_free(chand->service_config_json);
+  gpr_free(chand->info_lb_policy_name);
+  gpr_free(chand->info_service_config_json);
   if (chand->method_params_table != NULL) {
     grpc_slice_hash_table_unref(exec_ctx, chand->method_params_table);
   }
   grpc_connectivity_state_destroy(exec_ctx, &chand->state_tracker);
-  grpc_pollset_set_destroy(chand->interested_parties);
-  gpr_mu_destroy(&chand->mu);
+  grpc_pollset_set_destroy(exec_ctx, chand->interested_parties);
+  GRPC_COMBINER_UNREF(exec_ctx, chand->combiner, "client_channel");
+  gpr_mu_destroy(&chand->info_mu);
 }
 
 /*************************************************************************
@@ -615,8 +627,6 @@ typedef struct client_channel_call_data {
       grpc_subchannel_call */
   gpr_atm subchannel_call;
 
-  gpr_mu mu;
-
   subchannel_creation_phase creation_phase;
   grpc_connected_subchannel *connected_subchannel;
   grpc_polling_entity *pollent;
@@ -661,52 +671,32 @@ static void fail_locked(grpc_exec_ctx *exec_ctx, call_data *calld,
   GRPC_ERROR_UNREF(error);
 }
 
-typedef struct {
-  grpc_transport_stream_op **ops;
-  size_t nops;
-  grpc_subchannel_call *call;
-} retry_ops_args;
-
-static void retry_ops(grpc_exec_ctx *exec_ctx, void *args, grpc_error *error) {
-  retry_ops_args *a = args;
-  size_t i;
-  for (i = 0; i < a->nops; i++) {
-    grpc_subchannel_call_process_op(exec_ctx, a->call, a->ops[i]);
-  }
-  GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, a->call, "retry_ops");
-  gpr_free(a->ops);
-  gpr_free(a);
-}
-
 static void retry_waiting_locked(grpc_exec_ctx *exec_ctx, call_data *calld) {
   if (calld->waiting_ops_count == 0) {
     return;
   }
 
-  retry_ops_args *a = gpr_malloc(sizeof(*a));
-  a->ops = calld->waiting_ops;
-  a->nops = calld->waiting_ops_count;
-  a->call = GET_CALL(calld);
-  if (a->call == CANCELLED_CALL) {
-    gpr_free(a);
+  grpc_subchannel_call *call = GET_CALL(calld);
+  grpc_transport_stream_op **ops = calld->waiting_ops;
+  size_t nops = calld->waiting_ops_count;
+  if (call == CANCELLED_CALL) {
     fail_locked(exec_ctx, calld, GRPC_ERROR_CANCELLED);
     return;
   }
   calld->waiting_ops = NULL;
   calld->waiting_ops_count = 0;
   calld->waiting_ops_capacity = 0;
-  GRPC_SUBCHANNEL_CALL_REF(a->call, "retry_ops");
-  grpc_closure_sched(
-      exec_ctx, grpc_closure_create(retry_ops, a, grpc_schedule_on_exec_ctx),
-      GRPC_ERROR_NONE);
+  for (size_t i = 0; i < nops; i++) {
+    grpc_subchannel_call_process_op(exec_ctx, call, ops[i]);
+  }
+  gpr_free(ops);
 }
 
-static void subchannel_ready(grpc_exec_ctx *exec_ctx, void *arg,
-                             grpc_error *error) {
+static void subchannel_ready_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                    grpc_error *error) {
   grpc_call_element *elem = arg;
   call_data *calld = elem->call_data;
   channel_data *chand = elem->channel_data;
-  gpr_mu_lock(&calld->mu);
   GPR_ASSERT(calld->creation_phase ==
              GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL);
   grpc_polling_entity_del_from_pollset_set(exec_ctx, calld->pollent,
@@ -742,7 +732,6 @@ static void subchannel_ready(grpc_exec_ctx *exec_ctx, void *arg,
                       (gpr_atm)(uintptr_t)subchannel_call);
     retry_waiting_locked(exec_ctx, calld);
   }
-  gpr_mu_unlock(&calld->mu);
   GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call, "pick_subchannel");
 }
 
@@ -768,37 +757,35 @@ typedef struct {
 /** Return true if subchannel is available immediately (in which case on_ready
     should not be called), or false otherwise (in which case on_ready should be
     called when the subchannel is available). */
-static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
-                            grpc_metadata_batch *initial_metadata,
-                            uint32_t initial_metadata_flags,
-                            grpc_connected_subchannel **connected_subchannel,
-                            grpc_closure *on_ready, grpc_error *error);
-
-static void continue_picking(grpc_exec_ctx *exec_ctx, void *arg,
-                             grpc_error *error) {
+static bool pick_subchannel_locked(
+    grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+    grpc_metadata_batch *initial_metadata, uint32_t initial_metadata_flags,
+    grpc_connected_subchannel **connected_subchannel, grpc_closure *on_ready,
+    grpc_error *error);
+
+static void continue_picking_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                    grpc_error *error) {
   continue_picking_args *cpa = arg;
   if (cpa->connected_subchannel == NULL) {
     /* cancelled, do nothing */
   } else if (error != GRPC_ERROR_NONE) {
     grpc_closure_sched(exec_ctx, cpa->on_ready, GRPC_ERROR_REF(error));
   } else {
-    call_data *calld = cpa->elem->call_data;
-    gpr_mu_lock(&calld->mu);
-    if (pick_subchannel(exec_ctx, cpa->elem, cpa->initial_metadata,
-                        cpa->initial_metadata_flags, cpa->connected_subchannel,
-                        cpa->on_ready, GRPC_ERROR_NONE)) {
+    if (pick_subchannel_locked(exec_ctx, cpa->elem, cpa->initial_metadata,
+                               cpa->initial_metadata_flags,
+                               cpa->connected_subchannel, cpa->on_ready,
+                               GRPC_ERROR_NONE)) {
       grpc_closure_sched(exec_ctx, cpa->on_ready, GRPC_ERROR_NONE);
     }
-    gpr_mu_unlock(&calld->mu);
   }
   gpr_free(cpa);
 }
 
-static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
-                            grpc_metadata_batch *initial_metadata,
-                            uint32_t initial_metadata_flags,
-                            grpc_connected_subchannel **connected_subchannel,
-                            grpc_closure *on_ready, grpc_error *error) {
+static bool pick_subchannel_locked(
+    grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
+    grpc_metadata_batch *initial_metadata, uint32_t initial_metadata_flags,
+    grpc_connected_subchannel **connected_subchannel, grpc_closure *on_ready,
+    grpc_error *error) {
   GPR_TIMER_BEGIN("pick_subchannel", 0);
 
   channel_data *chand = elem->channel_data;
@@ -808,7 +795,6 @@ static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
 
   GPR_ASSERT(connected_subchannel);
 
-  gpr_mu_lock(&chand->mu);
   if (initial_metadata == NULL) {
     if (chand->lb_policy != NULL) {
       grpc_lb_policy_cancel_pick(exec_ctx, chand->lb_policy,
@@ -824,7 +810,6 @@ static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
             GRPC_ERROR_CREATE_REFERENCING("Pick cancelled", &error, 1));
       }
     }
-    gpr_mu_unlock(&chand->mu);
     GPR_TIMER_END("pick_subchannel", 0);
     GRPC_ERROR_UNREF(error);
     return true;
@@ -833,7 +818,6 @@ static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
   if (chand->lb_policy != NULL) {
     grpc_lb_policy *lb_policy = chand->lb_policy;
     GRPC_LB_POLICY_REF(lb_policy, "pick_subchannel");
-    gpr_mu_unlock(&chand->mu);
     // If the application explicitly set wait_for_ready, use that.
     // Otherwise, if the service config specified a value for this
     // method, use that.
@@ -872,88 +856,66 @@ static bool pick_subchannel(grpc_exec_ctx *exec_ctx, grpc_call_element *elem,
     cpa->connected_subchannel = connected_subchannel;
     cpa->on_ready = on_ready;
     cpa->elem = elem;
-    grpc_closure_init(&cpa->closure, continue_picking, cpa,
-                      grpc_schedule_on_exec_ctx);
+    grpc_closure_init(&cpa->closure, continue_picking_locked, cpa,
+                      grpc_combiner_scheduler(chand->combiner, true));
     grpc_closure_list_append(&chand->waiting_for_config_closures, &cpa->closure,
                              GRPC_ERROR_NONE);
   } else {
     grpc_closure_sched(exec_ctx, on_ready, GRPC_ERROR_CREATE("Disconnected"));
   }
-  gpr_mu_unlock(&chand->mu);
 
   GPR_TIMER_END("pick_subchannel", 0);
   return false;
 }
 
-// The logic here is fairly complicated, due to (a) the fact that we
-// need to handle the case where we receive the send op before the
-// initial metadata op, and (b) the need for efficiency, especially in
-// the streaming case.
-// TODO(ctiller): Explain this more thoroughly.
-static void cc_start_transport_stream_op(grpc_exec_ctx *exec_ctx,
-                                         grpc_call_element *elem,
-                                         grpc_transport_stream_op *op) {
-  call_data *calld = elem->call_data;
+static void start_transport_stream_op_locked_inner(grpc_exec_ctx *exec_ctx,
+                                                   grpc_transport_stream_op *op,
+                                                   grpc_call_element *elem) {
   channel_data *chand = elem->channel_data;
-  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
-  grpc_deadline_state_client_start_transport_stream_op(exec_ctx, elem, op);
-  /* try to (atomically) get the call */
-  grpc_subchannel_call *call = GET_CALL(calld);
-  GPR_TIMER_BEGIN("cc_start_transport_stream_op", 0);
-  if (call == CANCELLED_CALL) {
-    grpc_transport_stream_op_finish_with_failure(
-        exec_ctx, op, GRPC_ERROR_REF(calld->cancel_error));
-    GPR_TIMER_END("cc_start_transport_stream_op", 0);
-    return;
-  }
-  if (call != NULL) {
-    grpc_subchannel_call_process_op(exec_ctx, call, op);
-    GPR_TIMER_END("cc_start_transport_stream_op", 0);
-    return;
-  }
-  /* we failed; lock and figure out what to do */
-  gpr_mu_lock(&calld->mu);
-retry:
+  call_data *calld = elem->call_data;
+  grpc_subchannel_call *call;
+
   /* need to recheck that another thread hasn't set the call */
   call = GET_CALL(calld);
   if (call == CANCELLED_CALL) {
-    gpr_mu_unlock(&calld->mu);
     grpc_transport_stream_op_finish_with_failure(
         exec_ctx, op, GRPC_ERROR_REF(calld->cancel_error));
-    GPR_TIMER_END("cc_start_transport_stream_op", 0);
+    /* early out */
     return;
   }
   if (call != NULL) {
-    gpr_mu_unlock(&calld->mu);
     grpc_subchannel_call_process_op(exec_ctx, call, op);
-    GPR_TIMER_END("cc_start_transport_stream_op", 0);
+    /* early out */
     return;
   }
   /* if this is a cancellation, then we can raise our cancelled flag */
   if (op->cancel_error != GRPC_ERROR_NONE) {
     if (!gpr_atm_rel_cas(&calld->subchannel_call, 0,
                          (gpr_atm)(uintptr_t)CANCELLED_CALL)) {
-      goto retry;
+      /* recurse to retry */
+      start_transport_stream_op_locked_inner(exec_ctx, op, elem);
+      /* early out */
+      return;
     } else {
-      // Stash a copy of cancel_error in our call data, so that we can use
-      // it for subsequent operations.  This ensures that if the call is
-      // cancelled before any ops are passed down (e.g., if the deadline
-      // is in the past when the call starts), we can return the right
-      // error to the caller when the first op does get passed down.
+      /* Stash a copy of cancel_error in our call data, so that we can use
+         it for subsequent operations.  This ensures that if the call is
+         cancelled before any ops are passed down (e.g., if the deadline
+         is in the past when the call starts), we can return the right
+         error to the caller when the first op does get passed down. */
       calld->cancel_error = GRPC_ERROR_REF(op->cancel_error);
       switch (calld->creation_phase) {
         case GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING:
           fail_locked(exec_ctx, calld, GRPC_ERROR_REF(op->cancel_error));
           break;
         case GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL:
-          pick_subchannel(exec_ctx, elem, NULL, 0, &calld->connected_subchannel,
-                          NULL, GRPC_ERROR_REF(op->cancel_error));
+          pick_subchannel_locked(exec_ctx, elem, NULL, 0,
+                                 &calld->connected_subchannel, NULL,
+                                 GRPC_ERROR_REF(op->cancel_error));
           break;
       }
-      gpr_mu_unlock(&calld->mu);
       grpc_transport_stream_op_finish_with_failure(
           exec_ctx, op, GRPC_ERROR_REF(op->cancel_error));
-      GPR_TIMER_END("cc_start_transport_stream_op", 0);
+      /* early out */
       return;
     }
   }
@@ -962,16 +924,16 @@ retry:
       calld->connected_subchannel == NULL &&
       op->send_initial_metadata != NULL) {
     calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_PICKING_SUBCHANNEL;
-    grpc_closure_init(&calld->next_step, subchannel_ready, elem,
-                      grpc_schedule_on_exec_ctx);
+    grpc_closure_init(&calld->next_step, subchannel_ready_locked, elem,
+                      grpc_combiner_scheduler(chand->combiner, true));
     GRPC_CALL_STACK_REF(calld->owning_call, "pick_subchannel");
     /* If a subchannel is not available immediately, the polling entity from
        call_data should be provided to channel_data's interested_parties, so
        that IO of the lb_policy and resolver could be done under it. */
-    if (pick_subchannel(exec_ctx, elem, op->send_initial_metadata,
-                        op->send_initial_metadata_flags,
-                        &calld->connected_subchannel, &calld->next_step,
-                        GRPC_ERROR_NONE)) {
+    if (pick_subchannel_locked(exec_ctx, elem, op->send_initial_metadata,
+                               op->send_initial_metadata_flags,
+                               &calld->connected_subchannel, &calld->next_step,
+                               GRPC_ERROR_NONE)) {
       calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
       GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call, "pick_subchannel");
     } else {
@@ -994,31 +956,89 @@ retry:
     gpr_atm_rel_store(&calld->subchannel_call,
                       (gpr_atm)(uintptr_t)subchannel_call);
     retry_waiting_locked(exec_ctx, calld);
-    goto retry;
+    /* recurse to retry */
+    start_transport_stream_op_locked_inner(exec_ctx, op, elem);
+    /* early out */
+    return;
   }
   /* nothing to be done but wait */
   add_waiting_locked(calld, op);
-  gpr_mu_unlock(&calld->mu);
+}
+
+static void cc_start_transport_stream_op_locked(grpc_exec_ctx *exec_ctx,
+                                                void *arg,
+                                                grpc_error *error_ignored) {
+  GPR_TIMER_BEGIN("cc_start_transport_stream_op_locked", 0);
+
+  grpc_transport_stream_op *op = arg;
+  grpc_call_element *elem = op->handler_private.args[0];
+  call_data *calld = elem->call_data;
+
+  start_transport_stream_op_locked_inner(exec_ctx, op, elem);
+
+  GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call,
+                        "start_transport_stream_op");
+  GPR_TIMER_END("cc_start_transport_stream_op_locked", 0);
+}
+
+/* The logic here is fairly complicated, due to (a) the fact that we
+   need to handle the case where we receive the send op before the
+   initial metadata op, and (b) the need for efficiency, especially in
+   the streaming case.
+
+   We use double-checked locking to initially see if initialization has been
+   performed. If it has not, we acquire the combiner and perform initialization.
+   If it has, we proceed on the fast path. */
+static void cc_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;
+  GRPC_CALL_LOG_OP(GPR_INFO, elem, op);
+  grpc_deadline_state_client_start_transport_stream_op(exec_ctx, elem, op);
+  /* try to (atomically) get the call */
+  grpc_subchannel_call *call = GET_CALL(calld);
+  GPR_TIMER_BEGIN("cc_start_transport_stream_op", 0);
+  if (call == CANCELLED_CALL) {
+    grpc_transport_stream_op_finish_with_failure(
+        exec_ctx, op, GRPC_ERROR_REF(calld->cancel_error));
+    GPR_TIMER_END("cc_start_transport_stream_op", 0);
+    /* early out */
+    return;
+  }
+  if (call != NULL) {
+    grpc_subchannel_call_process_op(exec_ctx, call, op);
+    GPR_TIMER_END("cc_start_transport_stream_op", 0);
+    /* early out */
+    return;
+  }
+  /* we failed; lock and figure out what to do */
+  GRPC_CALL_STACK_REF(calld->owning_call, "start_transport_stream_op");
+  op->handler_private.args[0] = elem;
+  grpc_closure_sched(
+      exec_ctx,
+      grpc_closure_init(&op->handler_private.closure,
+                        cc_start_transport_stream_op_locked, op,
+                        grpc_combiner_scheduler(chand->combiner, false)),
+      GRPC_ERROR_NONE);
   GPR_TIMER_END("cc_start_transport_stream_op", 0);
 }
 
 // Gets data from the service config.  Invoked when the resolver returns
 // its initial result.
-static void read_service_config(grpc_exec_ctx *exec_ctx, void *arg,
-                                grpc_error *error) {
+static void read_service_config_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                       grpc_error *error) {
   grpc_call_element *elem = arg;
   channel_data *chand = elem->channel_data;
   call_data *calld = elem->call_data;
   // If this is an error, there's no point in looking at the service config.
   if (error == GRPC_ERROR_NONE) {
     // Get the method config table from channel data.
-    gpr_mu_lock(&chand->mu);
     grpc_slice_hash_table *method_params_table = NULL;
     if (chand->method_params_table != NULL) {
       method_params_table =
           grpc_slice_hash_table_ref(chand->method_params_table);
     }
-    gpr_mu_unlock(&chand->mu);
     // If the method config table was present, use it.
     if (method_params_table != NULL) {
       const method_parameters *method_params = grpc_method_config_table_get(
@@ -1028,7 +1048,6 @@ static void read_service_config(grpc_exec_ctx *exec_ctx, void *arg,
             gpr_time_cmp(method_params->timeout, gpr_time_0(GPR_TIMESPAN)) != 0;
         if (have_method_timeout ||
             method_params->wait_for_ready != WAIT_FOR_READY_UNSET) {
-          gpr_mu_lock(&calld->mu);
           if (have_method_timeout) {
             const gpr_timespec per_method_deadline =
                 gpr_time_add(calld->call_start_time, method_params->timeout);
@@ -1042,7 +1061,6 @@ static void read_service_config(grpc_exec_ctx *exec_ctx, void *arg,
             calld->wait_for_ready_from_service_config =
                 method_params->wait_for_ready;
           }
-          gpr_mu_unlock(&calld->mu);
         }
       }
       grpc_slice_hash_table_unref(exec_ctx, method_params_table);
@@ -1051,43 +1069,25 @@ static void read_service_config(grpc_exec_ctx *exec_ctx, void *arg,
   GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call, "read_service_config");
 }
 
-/* Constructor for call_data */
-static grpc_error *cc_init_call_elem(grpc_exec_ctx *exec_ctx,
-                                     grpc_call_element *elem,
-                                     grpc_call_element_args *args) {
+static void initial_read_service_config_locked(grpc_exec_ctx *exec_ctx,
+                                               void *arg,
+                                               grpc_error *error_ignored) {
+  grpc_call_element *elem = arg;
   channel_data *chand = elem->channel_data;
   call_data *calld = elem->call_data;
-  // Initialize data members.
-  grpc_deadline_state_init(exec_ctx, elem, args->call_stack);
-  calld->path = grpc_slice_ref_internal(args->path);
-  calld->call_start_time = args->start_time;
-  calld->deadline = gpr_convert_clock_type(args->deadline, GPR_CLOCK_MONOTONIC);
-  calld->wait_for_ready_from_service_config = WAIT_FOR_READY_UNSET;
-  calld->cancel_error = GRPC_ERROR_NONE;
-  gpr_atm_rel_store(&calld->subchannel_call, 0);
-  gpr_mu_init(&calld->mu);
-  calld->connected_subchannel = NULL;
-  calld->waiting_ops = NULL;
-  calld->waiting_ops_count = 0;
-  calld->waiting_ops_capacity = 0;
-  calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
-  calld->owning_call = args->call_stack;
-  calld->pollent = NULL;
   // If the resolver has already returned results, then we can access
   // the service config parameters immediately.  Otherwise, we need to
   // defer that work until the resolver returns an initial result.
   // TODO(roth): This code is almost but not quite identical to the code
   // in read_service_config() above.  It would be nice to find a way to
   // combine them, to avoid having to maintain it twice.
-  gpr_mu_lock(&chand->mu);
   if (chand->lb_policy != NULL) {
     // We already have a resolver result, so check for service config.
     if (chand->method_params_table != NULL) {
       grpc_slice_hash_table *method_params_table =
           grpc_slice_hash_table_ref(chand->method_params_table);
-      gpr_mu_unlock(&chand->mu);
       method_parameters *method_params = grpc_method_config_table_get(
-          exec_ctx, method_params_table, args->path);
+          exec_ctx, method_params_table, calld->path);
       if (method_params != NULL) {
         if (gpr_time_cmp(method_params->timeout,
                          gpr_time_0(GPR_CLOCK_MONOTONIC)) != 0) {
@@ -1101,24 +1101,53 @@ static grpc_error *cc_init_call_elem(grpc_exec_ctx *exec_ctx,
         }
       }
       grpc_slice_hash_table_unref(exec_ctx, method_params_table);
-    } else {
-      gpr_mu_unlock(&chand->mu);
     }
   } else {
     // We don't yet have a resolver result, so register a callback to
     // get the service config data once the resolver returns.
     // Take a reference to the call stack to be owned by the callback.
     GRPC_CALL_STACK_REF(calld->owning_call, "read_service_config");
-    grpc_closure_init(&calld->read_service_config, read_service_config, elem,
-                      grpc_schedule_on_exec_ctx);
+    grpc_closure_init(&calld->read_service_config, read_service_config_locked,
+                      elem, grpc_combiner_scheduler(chand->combiner, false));
     grpc_closure_list_append(&chand->waiting_for_config_closures,
                              &calld->read_service_config, GRPC_ERROR_NONE);
-    gpr_mu_unlock(&chand->mu);
   }
   // Start the deadline timer with the current deadline value.  If we
   // do not yet have service config data, then the timer may be reset
   // later.
   grpc_deadline_state_start(exec_ctx, elem, calld->deadline);
+  GRPC_CALL_STACK_UNREF(exec_ctx, calld->owning_call,
+                        "initial_read_service_config");
+}
+
+/* Constructor for call_data */
+static grpc_error *cc_init_call_elem(grpc_exec_ctx *exec_ctx,
+                                     grpc_call_element *elem,
+                                     grpc_call_element_args *args) {
+  channel_data *chand = elem->channel_data;
+  call_data *calld = elem->call_data;
+  // Initialize data members.
+  grpc_deadline_state_init(exec_ctx, elem, args->call_stack);
+  calld->path = grpc_slice_ref_internal(args->path);
+  calld->call_start_time = args->start_time;
+  calld->deadline = gpr_convert_clock_type(args->deadline, GPR_CLOCK_MONOTONIC);
+  calld->wait_for_ready_from_service_config = WAIT_FOR_READY_UNSET;
+  calld->cancel_error = GRPC_ERROR_NONE;
+  gpr_atm_rel_store(&calld->subchannel_call, 0);
+  calld->connected_subchannel = NULL;
+  calld->waiting_ops = NULL;
+  calld->waiting_ops_count = 0;
+  calld->waiting_ops_capacity = 0;
+  calld->creation_phase = GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING;
+  calld->owning_call = args->call_stack;
+  calld->pollent = NULL;
+  GRPC_CALL_STACK_REF(calld->owning_call, "initial_read_service_config");
+  grpc_closure_sched(
+      exec_ctx,
+      grpc_closure_init(&calld->read_service_config,
+                        initial_read_service_config_locked, elem,
+                        grpc_combiner_scheduler(chand->combiner, false)),
+      GRPC_ERROR_NONE);
   return GRPC_ERROR_NONE;
 }
 
@@ -1136,7 +1165,6 @@ static void cc_destroy_call_elem(grpc_exec_ctx *exec_ctx,
     GRPC_SUBCHANNEL_CALL_UNREF(exec_ctx, call, "client_channel_destroy_call");
   }
   GPR_ASSERT(calld->creation_phase == GRPC_SUBCHANNEL_CALL_HOLDER_NOT_CREATING);
-  gpr_mu_destroy(&calld->mu);
   GPR_ASSERT(calld->waiting_ops_count == 0);
   if (calld->connected_subchannel != NULL) {
     GRPC_CONNECTED_SUBCHANNEL_UNREF(exec_ctx, calld->connected_subchannel,
@@ -1172,26 +1200,36 @@ const grpc_channel_filter grpc_client_channel_filter = {
     "client-channel",
 };
 
+static void try_to_connect_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                  grpc_error *error_ignored) {
+  channel_data *chand = arg;
+  if (chand->lb_policy != NULL) {
+    grpc_lb_policy_exit_idle(exec_ctx, chand->lb_policy);
+  } else {
+    chand->exit_idle_when_lb_policy_arrives = true;
+    if (!chand->started_resolving && chand->resolver != NULL) {
+      GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
+      chand->started_resolving = true;
+      grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
+                         &chand->on_resolver_result_changed);
+    }
+  }
+  GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "try_to_connect");
+}
+
 grpc_connectivity_state grpc_client_channel_check_connectivity_state(
     grpc_exec_ctx *exec_ctx, grpc_channel_element *elem, int try_to_connect) {
   channel_data *chand = elem->channel_data;
-  grpc_connectivity_state out;
-  gpr_mu_lock(&chand->mu);
-  out = grpc_connectivity_state_check(&chand->state_tracker, NULL);
+  grpc_connectivity_state out =
+      grpc_connectivity_state_check(&chand->state_tracker);
   if (out == GRPC_CHANNEL_IDLE && try_to_connect) {
-    if (chand->lb_policy != NULL) {
-      grpc_lb_policy_exit_idle(exec_ctx, chand->lb_policy);
-    } else {
-      chand->exit_idle_when_lb_policy_arrives = true;
-      if (!chand->started_resolving && chand->resolver != NULL) {
-        GRPC_CHANNEL_STACK_REF(chand->owning_stack, "resolver");
-        chand->started_resolving = true;
-        grpc_resolver_next(exec_ctx, chand->resolver, &chand->resolver_result,
-                           &chand->on_resolver_result_changed);
-      }
-    }
+    GRPC_CHANNEL_STACK_REF(chand->owning_stack, "try_to_connect");
+    grpc_closure_sched(
+        exec_ctx,
+        grpc_closure_create(try_to_connect_locked, chand,
+                            grpc_combiner_scheduler(chand->combiner, false)),
+        GRPC_ERROR_NONE);
   }
-  gpr_mu_unlock(&chand->mu);
   return out;
 }
 
@@ -1199,6 +1237,7 @@ typedef struct {
   channel_data *chand;
   grpc_pollset *pollset;
   grpc_closure *on_complete;
+  grpc_connectivity_state *state;
   grpc_closure my_closure;
 } external_connectivity_watcher;
 
@@ -1211,7 +1250,16 @@ static void on_external_watch_complete(grpc_exec_ctx *exec_ctx, void *arg,
   GRPC_CHANNEL_STACK_UNREF(exec_ctx, w->chand->owning_stack,
                            "external_connectivity_watcher");
   gpr_free(w);
-  follow_up->cb(exec_ctx, follow_up->cb_arg, error);
+  grpc_closure_run(exec_ctx, follow_up, GRPC_ERROR_REF(error));
+}
+
+static void watch_connectivity_state_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                            grpc_error *error_ignored) {
+  external_connectivity_watcher *w = arg;
+  grpc_closure_init(&w->my_closure, on_external_watch_complete, w,
+                    grpc_schedule_on_exec_ctx);
+  grpc_connectivity_state_notify_on_state_change(
+      exec_ctx, &w->chand->state_tracker, w->state, &w->my_closure);
 }
 
 void grpc_client_channel_watch_connectivity_state(
@@ -1222,13 +1270,13 @@ void grpc_client_channel_watch_connectivity_state(
   w->chand = chand;
   w->pollset = pollset;
   w->on_complete = on_complete;
+  w->state = state;
   grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties, pollset);
-  grpc_closure_init(&w->my_closure, on_external_watch_complete, w,
-                    grpc_schedule_on_exec_ctx);
   GRPC_CHANNEL_STACK_REF(w->chand->owning_stack,
                          "external_connectivity_watcher");
-  gpr_mu_lock(&chand->mu);
-  grpc_connectivity_state_notify_on_state_change(
-      exec_ctx, &chand->state_tracker, state, &w->my_closure);
-  gpr_mu_unlock(&chand->mu);
+  grpc_closure_sched(
+      exec_ctx,
+      grpc_closure_init(&w->my_closure, watch_connectivity_state_locked, w,
+                        grpc_combiner_scheduler(chand->combiner, true)),
+      GRPC_ERROR_NONE);
 }
diff --git a/src/core/ext/client_channel/lb_policy.c b/src/core/ext/client_channel/lb_policy.c
index 45ee72e2f0..90401b586f 100644
--- a/src/core/ext/client_channel/lb_policy.c
+++ b/src/core/ext/client_channel/lb_policy.c
@@ -94,7 +94,7 @@ void grpc_lb_policy_weak_unref(grpc_exec_ctx *exec_ctx,
   gpr_atm old_val =
       ref_mutate(policy, -(gpr_atm)1, 1 REF_MUTATE_PASS_ARGS("WEAK_UNREF"));
   if (old_val == 1) {
-    grpc_pollset_set_destroy(policy->interested_parties);
+    grpc_pollset_set_destroy(exec_ctx, policy->interested_parties);
     policy->vtable->destroy(exec_ctx, policy);
   }
 }
diff --git a/src/core/ext/client_channel/subchannel.c b/src/core/ext/client_channel/subchannel.c
index aa036e883b..09c68a91dd 100644
--- a/src/core/ext/client_channel/subchannel.c
+++ b/src/core/ext/client_channel/subchannel.c
@@ -217,7 +217,7 @@ static void subchannel_destroy(grpc_exec_ctx *exec_ctx, void *arg,
   grpc_slice_unref_internal(exec_ctx, c->initial_connect_string);
   grpc_connectivity_state_destroy(exec_ctx, &c->state_tracker);
   grpc_connector_unref(exec_ctx, c->connector);
-  grpc_pollset_set_destroy(c->pollset_set);
+  grpc_pollset_set_destroy(exec_ctx, c->pollset_set);
   grpc_subchannel_key_destroy(exec_ctx, c->key);
   gpr_free(c);
 }
@@ -419,7 +419,7 @@ grpc_connectivity_state grpc_subchannel_check_connectivity(grpc_subchannel *c,
                                                            grpc_error **error) {
   grpc_connectivity_state state;
   gpr_mu_lock(&c->mu);
-  state = grpc_connectivity_state_check(&c->state_tracker, error);
+  state = grpc_connectivity_state_get(&c->state_tracker, error);
   gpr_mu_unlock(&c->mu);
   return state;
 }
diff --git a/src/core/ext/lb_policy/grpclb/grpclb.c b/src/core/ext/lb_policy/grpclb/grpclb.c
index ab62e5ed6a..8a2af48328 100644
--- a/src/core/ext/lb_policy/grpclb/grpclb.c
+++ b/src/core/ext/lb_policy/grpclb/grpclb.c
@@ -492,9 +492,8 @@ static grpc_lb_addresses *process_serverlist_locked(
 static bool update_lb_connectivity_status_locked(
     grpc_exec_ctx *exec_ctx, glb_lb_policy *glb_policy,
     grpc_connectivity_state new_rr_state, grpc_error *new_rr_state_error) {
-  grpc_error *curr_state_error;
-  const grpc_connectivity_state curr_glb_state = grpc_connectivity_state_check(
-      &glb_policy->state_tracker, &curr_state_error);
+  const grpc_connectivity_state curr_glb_state =
+      grpc_connectivity_state_check(&glb_policy->state_tracker);
 
   /* The new connectivity status is a function of the previous one and the new
    * input coming from the status of the RR policy.
@@ -1098,8 +1097,8 @@ static grpc_connectivity_state glb_check_connectivity(
   glb_lb_policy *glb_policy = (glb_lb_policy *)pol;
   grpc_connectivity_state st;
   gpr_mu_lock(&glb_policy->mu);
-  st = grpc_connectivity_state_check(&glb_policy->state_tracker,
-                                     connectivity_error);
+  st = grpc_connectivity_state_get(&glb_policy->state_tracker,
+                                   connectivity_error);
   gpr_mu_unlock(&glb_policy->mu);
   return st;
 }
diff --git a/src/core/ext/lb_policy/pick_first/pick_first.c b/src/core/ext/lb_policy/pick_first/pick_first.c
index 9f2aa461be..1b965183f6 100644
--- a/src/core/ext/lb_policy/pick_first/pick_first.c
+++ b/src/core/ext/lb_policy/pick_first/pick_first.c
@@ -398,7 +398,7 @@ static grpc_connectivity_state pf_check_connectivity(grpc_exec_ctx *exec_ctx,
   pick_first_lb_policy *p = (pick_first_lb_policy *)pol;
   grpc_connectivity_state st;
   gpr_mu_lock(&p->mu);
-  st = grpc_connectivity_state_check(&p->state_tracker, error);
+  st = grpc_connectivity_state_get(&p->state_tracker, error);
   gpr_mu_unlock(&p->mu);
   return st;
 }
diff --git a/src/core/ext/lb_policy/round_robin/round_robin.c b/src/core/ext/lb_policy/round_robin/round_robin.c
index 3e060d189a..63e3d033ad 100644
--- a/src/core/ext/lb_policy/round_robin/round_robin.c
+++ b/src/core/ext/lb_policy/round_robin/round_robin.c
@@ -655,7 +655,7 @@ static grpc_connectivity_state rr_check_connectivity(grpc_exec_ctx *exec_ctx,
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   grpc_connectivity_state st;
   gpr_mu_lock(&p->mu);
-  st = grpc_connectivity_state_check(&p->state_tracker, error);
+  st = grpc_connectivity_state_get(&p->state_tracker, error);
   gpr_mu_unlock(&p->mu);
   return st;
 }
diff --git a/src/core/ext/resolver/dns/native/dns_resolver.c b/src/core/ext/resolver/dns/native/dns_resolver.c
index 2c9623211b..c08b53ea04 100644
--- a/src/core/ext/resolver/dns/native/dns_resolver.c
+++ b/src/core/ext/resolver/dns/native/dns_resolver.c
@@ -244,7 +244,7 @@ static void dns_destroy(grpc_exec_ctx *exec_ctx, grpc_resolver *gr) {
   if (r->resolved_result != NULL) {
     grpc_channel_args_destroy(exec_ctx, r->resolved_result);
   }
-  grpc_pollset_set_destroy(r->interested_parties);
+  grpc_pollset_set_destroy(exec_ctx, r->interested_parties);
   gpr_free(r->name_to_resolve);
   gpr_free(r->default_port);
   grpc_channel_args_destroy(exec_ctx, r->channel_args);
diff --git a/src/core/ext/transport/chttp2/transport/chttp2_transport.c b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
index ddbc656b96..d1fab25478 100644
--- a/src/core/ext/transport/chttp2/transport/chttp2_transport.c
+++ b/src/core/ext/transport/chttp2/transport/chttp2_transport.c
@@ -1041,8 +1041,8 @@ static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
   GPR_TIMER_BEGIN("perform_stream_op_locked", 0);
 
   grpc_transport_stream_op *op = stream_op;
-  grpc_chttp2_transport *t = op->transport_private.args[0];
-  grpc_chttp2_stream *s = op->transport_private.args[1];
+  grpc_chttp2_transport *t = op->handler_private.args[0];
+  grpc_chttp2_stream *s = op->handler_private.args[1];
 
   if (grpc_http_trace) {
     char *str = grpc_transport_stream_op_string(op);
@@ -1263,13 +1263,13 @@ static void perform_stream_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
     gpr_free(str);
   }
 
-  op->transport_private.args[0] = gt;
-  op->transport_private.args[1] = gs;
+  op->handler_private.args[0] = gt;
+  op->handler_private.args[1] = gs;
   GRPC_CHTTP2_STREAM_REF(s, "perform_stream_op");
   grpc_closure_sched(
       exec_ctx,
       grpc_closure_init(
-          &op->transport_private.closure, perform_stream_op_locked, op,
+          &op->handler_private.closure, perform_stream_op_locked, op,
           grpc_combiner_scheduler(t->combiner, op->covered_by_poller)),
       GRPC_ERROR_NONE);
   GPR_TIMER_END("perform_stream_op", 0);
diff --git a/src/core/lib/http/httpcli.c b/src/core/lib/http/httpcli.c
index fb2108987b..6d7aa43b81 100644
--- a/src/core/lib/http/httpcli.c
+++ b/src/core/lib/http/httpcli.c
@@ -93,8 +93,9 @@ void grpc_httpcli_context_init(grpc_httpcli_context *context) {
   context->pollset_set = grpc_pollset_set_create();
 }
 
-void grpc_httpcli_context_destroy(grpc_httpcli_context *context) {
-  grpc_pollset_set_destroy(context->pollset_set);
+void grpc_httpcli_context_destroy(grpc_exec_ctx *exec_ctx,
+                                  grpc_httpcli_context *context) {
+  grpc_pollset_set_destroy(exec_ctx, context->pollset_set);
 }
 
 static void next_address(grpc_exec_ctx *exec_ctx, internal_request *req,
diff --git a/src/core/lib/http/httpcli.h b/src/core/lib/http/httpcli.h
index 11e03b44df..8ae03ee78f 100644
--- a/src/core/lib/http/httpcli.h
+++ b/src/core/lib/http/httpcli.h
@@ -83,7 +83,8 @@ typedef struct grpc_httpcli_request {
 typedef struct grpc_http_response grpc_httpcli_response;
 
 void grpc_httpcli_context_init(grpc_httpcli_context *context);
-void grpc_httpcli_context_destroy(grpc_httpcli_context *context);
+void grpc_httpcli_context_destroy(grpc_exec_ctx *exec_ctx,
+                                  grpc_httpcli_context *context);
 
 /* Asynchronously perform a HTTP GET.
    'context' specifies the http context under which to do the get
diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index fc56843128..fac3705142 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -1842,13 +1842,12 @@ static grpc_pollset_set *pollset_set_create(void) {
   return pss;
 }
 
-static void pollset_set_destroy(grpc_pollset_set *pss) {
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pss) {
   gpr_mu_destroy(&pss->po.mu);
 
   if (pss->po.pi != NULL) {
-    grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    PI_UNREF(&exec_ctx, pss->po.pi, "pss_destroy");
-    grpc_exec_ctx_finish(&exec_ctx);
+    PI_UNREF(exec_ctx, pss->po.pi, "pss_destroy");
   }
 
   gpr_free(pss);
diff --git a/src/core/lib/iomgr/ev_poll_posix.c b/src/core/lib/iomgr/ev_poll_posix.c
index 21eb62753e..c03fadaebb 100644
--- a/src/core/lib/iomgr/ev_poll_posix.c
+++ b/src/core/lib/iomgr/ev_poll_posix.c
@@ -149,7 +149,7 @@ static void fd_end_poll(grpc_exec_ctx *exec_ctx, grpc_fd_watcher *rec,
 static bool fd_is_orphaned(grpc_fd *fd);
 
 /* Reference counting for fds */
-/*#define GRPC_FD_REF_COUNT_DEBUG*/
+//#define GRPC_FD_REF_COUNT_DEBUG
 #ifdef GRPC_FD_REF_COUNT_DEBUG
 static void fd_ref(grpc_fd *fd, const char *reason, const char *file, int line);
 static void fd_unref(grpc_fd *fd, const char *reason, const char *file,
@@ -191,6 +191,7 @@ struct grpc_pollset {
   int kicked_without_pollers;
   grpc_closure *shutdown_done;
   grpc_closure_list idle_jobs;
+  int pollset_set_count;
   /* all polled fds */
   size_t fd_count;
   size_t fd_capacity;
@@ -228,7 +229,7 @@ static grpc_error *pollset_kick_ext(grpc_pollset *p,
 
 /* Return 1 if the pollset has active threads in pollset_work (pollset must
  * be locked) */
-static int pollset_has_workers(grpc_pollset *pollset);
+static bool pollset_has_workers(grpc_pollset *pollset);
 
 /*******************************************************************************
  * pollset_set definitions
@@ -282,8 +283,8 @@ cv_fd_table g_cvfds;
 static void ref_by(grpc_fd *fd, int n, const char *reason, const char *file,
                    int line) {
   gpr_log(GPR_DEBUG, "FD %d %p   ref %d %d -> %d [%s; %s:%d]", fd->fd, fd, n,
-          gpr_atm_no_barrier_load(&fd->refst),
-          gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
+          (int)gpr_atm_no_barrier_load(&fd->refst),
+          (int)gpr_atm_no_barrier_load(&fd->refst) + n, reason, file, line);
 #else
 #define REF_BY(fd, n, reason) ref_by(fd, n)
 #define UNREF_BY(fd, n, reason) unref_by(fd, n)
@@ -297,8 +298,8 @@ static void unref_by(grpc_fd *fd, int n, const char *reason, const char *file,
                      int line) {
   gpr_atm old;
   gpr_log(GPR_DEBUG, "FD %d %p unref %d %d -> %d [%s; %s:%d]", fd->fd, fd, n,
-          gpr_atm_no_barrier_load(&fd->refst),
-          gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
+          (int)gpr_atm_no_barrier_load(&fd->refst),
+          (int)gpr_atm_no_barrier_load(&fd->refst) - n, reason, file, line);
 #else
 static void unref_by(grpc_fd *fd, int n) {
   gpr_atm old;
@@ -658,10 +659,18 @@ static void remove_worker(grpc_pollset *p, grpc_pollset_worker *worker) {
   worker->next->prev = worker->prev;
 }
 
-static int pollset_has_workers(grpc_pollset *p) {
+static bool pollset_has_workers(grpc_pollset *p) {
   return p->root_worker.next != &p->root_worker;
 }
 
+static bool pollset_in_pollset_sets(grpc_pollset *p) {
+  return p->pollset_set_count;
+}
+
+static bool pollset_has_observers(grpc_pollset *p) {
+  return pollset_has_workers(p) || pollset_in_pollset_sets(p);
+}
+
 static grpc_pollset_worker *pop_front_worker(grpc_pollset *p) {
   if (pollset_has_workers(p)) {
     grpc_pollset_worker *w = p->root_worker.next;
@@ -800,6 +809,7 @@ static void pollset_init(grpc_pollset *pollset, gpr_mu **mu) {
   pollset->fd_count = 0;
   pollset->fd_capacity = 0;
   pollset->fds = NULL;
+  pollset->pollset_set_count = 0;
 }
 
 static void pollset_destroy(grpc_pollset *pollset) {
@@ -1061,7 +1071,7 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   if (pollset->shutting_down) {
     if (pollset_has_workers(pollset)) {
       pollset_kick(pollset, NULL);
-    } else if (!pollset->called_shutdown) {
+    } else if (!pollset->called_shutdown && !pollset_has_observers(pollset)) {
       pollset->called_shutdown = 1;
       gpr_mu_unlock(&pollset->mu);
       finish_shutdown(exec_ctx, pollset);
@@ -1093,7 +1103,7 @@ static void pollset_shutdown(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
   if (!pollset_has_workers(pollset)) {
     grpc_closure_list_sched(exec_ctx, &pollset->idle_jobs);
   }
-  if (!pollset->called_shutdown && !pollset_has_workers(pollset)) {
+  if (!pollset->called_shutdown && !pollset_has_observers(pollset)) {
     pollset->called_shutdown = 1;
     finish_shutdown(exec_ctx, pollset);
   }
@@ -1127,12 +1137,27 @@ static grpc_pollset_set *pollset_set_create(void) {
   return pollset_set;
 }
 
-static void pollset_set_destroy(grpc_pollset_set *pollset_set) {
+static void pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                                grpc_pollset_set *pollset_set) {
   size_t i;
   gpr_mu_destroy(&pollset_set->mu);
   for (i = 0; i < pollset_set->fd_count; i++) {
     GRPC_FD_UNREF(pollset_set->fds[i], "pollset_set");
   }
+  for (i = 0; i < pollset_set->pollset_count; i++) {
+    grpc_pollset *pollset = pollset_set->pollsets[i];
+    gpr_mu_lock(&pollset->mu);
+    pollset->pollset_set_count--;
+    /* check shutdown */
+    if (pollset->shutting_down && !pollset->called_shutdown &&
+        !pollset_has_observers(pollset)) {
+      pollset->called_shutdown = 1;
+      gpr_mu_unlock(&pollset->mu);
+      finish_shutdown(exec_ctx, pollset);
+    } else {
+      gpr_mu_unlock(&pollset->mu);
+    }
+  }
   gpr_free(pollset_set->pollsets);
   gpr_free(pollset_set->pollset_sets);
   gpr_free(pollset_set->fds);
@@ -1143,6 +1168,9 @@ static void pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
                                     grpc_pollset_set *pollset_set,
                                     grpc_pollset *pollset) {
   size_t i, j;
+  gpr_mu_lock(&pollset->mu);
+  pollset->pollset_set_count++;
+  gpr_mu_unlock(&pollset->mu);
   gpr_mu_lock(&pollset_set->mu);
   if (pollset_set->pollset_count == pollset_set->pollset_capacity) {
     pollset_set->pollset_capacity =
@@ -1178,6 +1206,17 @@ static void pollset_set_del_pollset(grpc_exec_ctx *exec_ctx,
     }
   }
   gpr_mu_unlock(&pollset_set->mu);
+  gpr_mu_lock(&pollset->mu);
+  pollset->pollset_set_count--;
+  /* check shutdown */
+  if (pollset->shutting_down && !pollset->called_shutdown &&
+      !pollset_has_observers(pollset)) {
+    pollset->called_shutdown = 1;
+    gpr_mu_unlock(&pollset->mu);
+    finish_shutdown(exec_ctx, pollset);
+  } else {
+    gpr_mu_unlock(&pollset->mu);
+  }
 }
 
 static void pollset_set_add_pollset_set(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index 95b1d99d75..b5be5504b9 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -215,8 +215,9 @@ grpc_pollset_set *grpc_pollset_set_create(void) {
   return g_event_engine->pollset_set_create();
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set *pollset_set) {
-  g_event_engine->pollset_set_destroy(pollset_set);
+void grpc_pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set) {
+  g_event_engine->pollset_set_destroy(exec_ctx, pollset_set);
 }
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index 1aea7d61f3..1a9e5c115a 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -74,7 +74,8 @@ typedef struct grpc_event_engine_vtable {
                          struct grpc_fd *fd);
 
   grpc_pollset_set *(*pollset_set_create)(void);
-  void (*pollset_set_destroy)(grpc_pollset_set *pollset_set);
+  void (*pollset_set_destroy)(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set);
   void (*pollset_set_add_pollset)(grpc_exec_ctx *exec_ctx,
                                   grpc_pollset_set *pollset_set,
                                   grpc_pollset *pollset);
diff --git a/src/core/lib/iomgr/pollset_set.h b/src/core/lib/iomgr/pollset_set.h
index 34bb728c41..d11801d63b 100644
--- a/src/core/lib/iomgr/pollset_set.h
+++ b/src/core/lib/iomgr/pollset_set.h
@@ -44,7 +44,8 @@
 typedef struct grpc_pollset_set grpc_pollset_set;
 
 grpc_pollset_set *grpc_pollset_set_create(void);
-void grpc_pollset_set_destroy(grpc_pollset_set *pollset_set);
+void grpc_pollset_set_destroy(grpc_exec_ctx *exec_ctx,
+                              grpc_pollset_set *pollset_set);
 void grpc_pollset_set_add_pollset(grpc_exec_ctx *exec_ctx,
                                   grpc_pollset_set *pollset_set,
                                   grpc_pollset *pollset);
diff --git a/src/core/lib/iomgr/pollset_set_uv.c b/src/core/lib/iomgr/pollset_set_uv.c
index e5ef8b29e0..836cfee4ef 100644
--- a/src/core/lib/iomgr/pollset_set_uv.c
+++ b/src/core/lib/iomgr/pollset_set_uv.c
@@ -41,7 +41,8 @@ grpc_pollset_set* grpc_pollset_set_create(void) {
   return (grpc_pollset_set*)((intptr_t)0xdeafbeef);
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set* pollset_set) {}
+void grpc_pollset_set_destroy(grpc_exec_ctx* exec_ctx,
+                              grpc_pollset_set* pollset_set) {}
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx* exec_ctx,
                                   grpc_pollset_set* pollset_set,
diff --git a/src/core/lib/iomgr/pollset_set_windows.c b/src/core/lib/iomgr/pollset_set_windows.c
index 645650db9b..ae18c8a3ce 100644
--- a/src/core/lib/iomgr/pollset_set_windows.c
+++ b/src/core/lib/iomgr/pollset_set_windows.c
@@ -42,7 +42,8 @@ grpc_pollset_set* grpc_pollset_set_create(void) {
   return (grpc_pollset_set*)((intptr_t)0xdeafbeef);
 }
 
-void grpc_pollset_set_destroy(grpc_pollset_set* pollset_set) {}
+void grpc_pollset_set_destroy(grpc_exec_ctx* exec_ctx,
+                              grpc_pollset_set* pollset_set) {}
 
 void grpc_pollset_set_add_pollset(grpc_exec_ctx* exec_ctx,
                                   grpc_pollset_set* pollset_set,
diff --git a/src/core/lib/security/credentials/google_default/google_default_credentials.c b/src/core/lib/security/credentials/google_default/google_default_credentials.c
index a098741b70..ecd26de9fa 100644
--- a/src/core/lib/security/credentials/google_default/google_default_credentials.c
+++ b/src/core/lib/security/credentials/google_default/google_default_credentials.c
@@ -154,7 +154,7 @@ static int is_stack_running_on_compute_engine(grpc_exec_ctx *exec_ctx) {
   }
   gpr_mu_unlock(g_polling_mu);
 
-  grpc_httpcli_context_destroy(&context);
+  grpc_httpcli_context_destroy(exec_ctx, &context);
   grpc_closure_init(&destroy_closure, destroy_pollset,
                     grpc_polling_entity_pollset(&detector.pollent),
                     grpc_schedule_on_exec_ctx);
diff --git a/src/core/lib/security/credentials/jwt/jwt_verifier.c b/src/core/lib/security/credentials/jwt/jwt_verifier.c
index 2270be8f44..f128177e8c 100644
--- a/src/core/lib/security/credentials/jwt/jwt_verifier.c
+++ b/src/core/lib/security/credentials/jwt/jwt_verifier.c
@@ -898,10 +898,10 @@ grpc_jwt_verifier *grpc_jwt_verifier_create(
   return v;
 }
 
-void grpc_jwt_verifier_destroy(grpc_jwt_verifier *v) {
+void grpc_jwt_verifier_destroy(grpc_exec_ctx *exec_ctx, grpc_jwt_verifier *v) {
   size_t i;
   if (v == NULL) return;
-  grpc_httpcli_context_destroy(&v->http_ctx);
+  grpc_httpcli_context_destroy(exec_ctx, &v->http_ctx);
   if (v->mappings != NULL) {
     for (i = 0; i < v->num_mappings; i++) {
       gpr_free(v->mappings[i].email_domain);
diff --git a/src/core/lib/security/credentials/jwt/jwt_verifier.h b/src/core/lib/security/credentials/jwt/jwt_verifier.h
index 4fa320a415..5c3d2a7788 100644
--- a/src/core/lib/security/credentials/jwt/jwt_verifier.h
+++ b/src/core/lib/security/credentials/jwt/jwt_verifier.h
@@ -109,7 +109,8 @@ grpc_jwt_verifier *grpc_jwt_verifier_create(
     size_t num_mappings);
 
 /*The verifier must not be destroyed if there are still outstanding callbacks.*/
-void grpc_jwt_verifier_destroy(grpc_jwt_verifier *verifier);
+void grpc_jwt_verifier_destroy(grpc_exec_ctx *exec_ctx,
+                               grpc_jwt_verifier *verifier);
 
 /* User provided callback that will be called when the verification of the JWT
    is done (maybe in another thread).
diff --git a/src/core/lib/security/credentials/oauth2/oauth2_credentials.c b/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
index 1b0e43a1e4..c0f260f938 100644
--- a/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
+++ b/src/core/lib/security/credentials/oauth2/oauth2_credentials.c
@@ -124,7 +124,7 @@ static void oauth2_token_fetcher_destruct(grpc_exec_ctx *exec_ctx,
       (grpc_oauth2_token_fetcher_credentials *)creds;
   grpc_credentials_md_store_unref(exec_ctx, c->access_token_md);
   gpr_mu_destroy(&c->mu);
-  grpc_httpcli_context_destroy(&c->httpcli_context);
+  grpc_httpcli_context_destroy(exec_ctx, &c->httpcli_context);
 }
 
 grpc_credentials_status
diff --git a/src/core/lib/transport/connectivity_state.c b/src/core/lib/transport/connectivity_state.c
index 8fc5bf3e9a..afe1f6164d 100644
--- a/src/core/lib/transport/connectivity_state.c
+++ b/src/core/lib/transport/connectivity_state.c
@@ -62,7 +62,7 @@ const char *grpc_connectivity_state_name(grpc_connectivity_state state) {
 void grpc_connectivity_state_init(grpc_connectivity_state_tracker *tracker,
                                   grpc_connectivity_state init_state,
                                   const char *name) {
-  tracker->current_state = init_state;
+  gpr_atm_no_barrier_store(&tracker->current_state_atm, init_state);
   tracker->current_error = GRPC_ERROR_NONE;
   tracker->watchers = NULL;
   tracker->name = gpr_strdup(name);
@@ -89,15 +89,30 @@ void grpc_connectivity_state_destroy(grpc_exec_ctx *exec_ctx,
 }
 
 grpc_connectivity_state grpc_connectivity_state_check(
+    grpc_connectivity_state_tracker *tracker) {
+  grpc_connectivity_state cur =
+      (grpc_connectivity_state)gpr_atm_no_barrier_load(
+          &tracker->current_state_atm);
+  if (grpc_connectivity_state_trace) {
+    gpr_log(GPR_DEBUG, "CONWATCH: %p %s: get %s", tracker, tracker->name,
+            grpc_connectivity_state_name(cur));
+  }
+  return cur;
+}
+
+grpc_connectivity_state grpc_connectivity_state_get(
     grpc_connectivity_state_tracker *tracker, grpc_error **error) {
+  grpc_connectivity_state cur =
+      (grpc_connectivity_state)gpr_atm_no_barrier_load(
+          &tracker->current_state_atm);
   if (grpc_connectivity_state_trace) {
     gpr_log(GPR_DEBUG, "CONWATCH: %p %s: get %s", tracker, tracker->name,
-            grpc_connectivity_state_name(tracker->current_state));
+            grpc_connectivity_state_name(cur));
   }
   if (error != NULL) {
     *error = GRPC_ERROR_REF(tracker->current_error);
   }
-  return tracker->current_state;
+  return cur;
 }
 
 bool grpc_connectivity_state_has_watchers(
@@ -108,6 +123,9 @@ bool grpc_connectivity_state_has_watchers(
 bool grpc_connectivity_state_notify_on_state_change(
     grpc_exec_ctx *exec_ctx, grpc_connectivity_state_tracker *tracker,
     grpc_connectivity_state *current, grpc_closure *notify) {
+  grpc_connectivity_state cur =
+      (grpc_connectivity_state)gpr_atm_no_barrier_load(
+          &tracker->current_state_atm);
   if (grpc_connectivity_state_trace) {
     if (current == NULL) {
       gpr_log(GPR_DEBUG, "CONWATCH: %p %s: unsubscribe notify=%p", tracker,
@@ -115,7 +133,7 @@ bool grpc_connectivity_state_notify_on_state_change(
     } else {
       gpr_log(GPR_DEBUG, "CONWATCH: %p %s: from %s [cur=%s] notify=%p", tracker,
               tracker->name, grpc_connectivity_state_name(*current),
-              grpc_connectivity_state_name(tracker->current_state), notify);
+              grpc_connectivity_state_name(cur), notify);
     }
   }
   if (current == NULL) {
@@ -138,8 +156,8 @@ bool grpc_connectivity_state_notify_on_state_change(
     }
     return false;
   } else {
-    if (tracker->current_state != *current) {
-      *current = tracker->current_state;
+    if (cur != *current) {
+      *current = cur;
       grpc_closure_sched(exec_ctx, notify,
                          GRPC_ERROR_REF(tracker->current_error));
     } else {
@@ -149,7 +167,7 @@ bool grpc_connectivity_state_notify_on_state_change(
       w->next = tracker->watchers;
       tracker->watchers = w;
     }
-    return tracker->current_state == GRPC_CHANNEL_IDLE;
+    return cur == GRPC_CHANNEL_IDLE;
   }
 }
 
@@ -157,11 +175,14 @@ void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
                                  grpc_connectivity_state_tracker *tracker,
                                  grpc_connectivity_state state,
                                  grpc_error *error, const char *reason) {
+  grpc_connectivity_state cur =
+      (grpc_connectivity_state)gpr_atm_no_barrier_load(
+          &tracker->current_state_atm);
   grpc_connectivity_state_watcher *w;
   if (grpc_connectivity_state_trace) {
     const char *error_string = grpc_error_string(error);
     gpr_log(GPR_DEBUG, "SET: %p %s: %s --> %s [%s] error=%p %s", tracker,
-            tracker->name, grpc_connectivity_state_name(tracker->current_state),
+            tracker->name, grpc_connectivity_state_name(cur),
             grpc_connectivity_state_name(state), reason, error, error_string);
   }
   switch (state) {
@@ -178,13 +199,13 @@ void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
   }
   GRPC_ERROR_UNREF(tracker->current_error);
   tracker->current_error = error;
-  if (tracker->current_state == state) {
+  if (cur == state) {
     return;
   }
-  GPR_ASSERT(tracker->current_state != GRPC_CHANNEL_SHUTDOWN);
-  tracker->current_state = state;
+  GPR_ASSERT(cur != GRPC_CHANNEL_SHUTDOWN);
+  gpr_atm_no_barrier_store(&tracker->current_state_atm, state);
   while ((w = tracker->watchers) != NULL) {
-    *w->current = tracker->current_state;
+    *w->current = state;
     tracker->watchers = w->next;
     if (grpc_connectivity_state_trace) {
       gpr_log(GPR_DEBUG, "NOTIFY: %p %s: %p", tracker, tracker->name,
diff --git a/src/core/lib/transport/connectivity_state.h b/src/core/lib/transport/connectivity_state.h
index 769c675b79..c9604c34dd 100644
--- a/src/core/lib/transport/connectivity_state.h
+++ b/src/core/lib/transport/connectivity_state.h
@@ -47,8 +47,8 @@ typedef struct grpc_connectivity_state_watcher {
 } grpc_connectivity_state_watcher;
 
 typedef struct {
-  /** current connectivity state */
-  grpc_connectivity_state current_state;
+  /** current grpc_connectivity_state */
+  gpr_atm current_state_atm;
   /** error associated with state */
   grpc_error *current_error;
   /** all our watchers */
@@ -59,6 +59,7 @@ typedef struct {
 
 extern int grpc_connectivity_state_trace;
 
+/** enum --> string conversion */
 const char *grpc_connectivity_state_name(grpc_connectivity_state state);
 
 void grpc_connectivity_state_init(grpc_connectivity_state_tracker *tracker,
@@ -68,22 +69,31 @@ void grpc_connectivity_state_destroy(grpc_exec_ctx *exec_ctx,
                                      grpc_connectivity_state_tracker *tracker);
 
 /** Set connectivity state; not thread safe; access must be serialized with an
- * external lock */
+ *  external lock */
 void grpc_connectivity_state_set(grpc_exec_ctx *exec_ctx,
                                  grpc_connectivity_state_tracker *tracker,
                                  grpc_connectivity_state state,
                                  grpc_error *associated_error,
                                  const char *reason);
 
+/** Return true if this connectivity state has watchers.
+    Access must be serialized with an external lock. */
 bool grpc_connectivity_state_has_watchers(
     grpc_connectivity_state_tracker *tracker);
 
+/** Return the last seen connectivity state. No need to synchronize access. */
 grpc_connectivity_state grpc_connectivity_state_check(
-    grpc_connectivity_state_tracker *tracker, grpc_error **current_error);
+    grpc_connectivity_state_tracker *tracker);
+
+/** Return the last seen connectivity state, and the associated error.
+    Access must be serialized with an external lock. */
+grpc_connectivity_state grpc_connectivity_state_get(
+    grpc_connectivity_state_tracker *tracker, grpc_error **error);
 
 /** Return 1 if the channel should start connecting, 0 otherwise.
     If current==NULL cancel notify if it is already queued (success==0 in that
-    case) */
+    case).
+    Access must be serialized with an external lock. */
 bool grpc_connectivity_state_notify_on_state_change(
     grpc_exec_ctx *exec_ctx, grpc_connectivity_state_tracker *tracker,
     grpc_connectivity_state *current, grpc_closure *notify);
diff --git a/src/core/lib/transport/transport.h b/src/core/lib/transport/transport.h
index 9a0abe1ca4..e56bf2780a 100644
--- a/src/core/lib/transport/transport.h
+++ b/src/core/lib/transport/transport.h
@@ -167,9 +167,9 @@ typedef struct grpc_transport_stream_op {
 
   /***************************************************************************
    * remaining fields are initialized and used at the discretion of the
-   * transport implementation */
+   * current handler of the op */
 
-  grpc_transport_private_op_data transport_private;
+  grpc_transport_private_op_data handler_private;
 } grpc_transport_stream_op;
 
 /** Transport op: a set of operations to perform on a transport as a whole */