Merge github.com:grpc/grpc into newlines

11 files changed, 269 insertions, 50 deletions

diff --git a/src/core/lib/iomgr/network_status_tracker.c b/src/core/lib/iomgr/network_status_tracker.c
index b4bb7e3cf7..a5ca9ed2c3 100644
--- a/src/core/lib/iomgr/network_status_tracker.c
+++ b/src/core/lib/iomgr/network_status_tracker.c
@@ -46,7 +46,7 @@ static gpr_mu g_endpoint_mutex;
 void grpc_network_status_shutdown(void) {
   if (head != NULL) {
     gpr_log(GPR_ERROR,
-            "Memory leaked as all network endpoints were not shut down");
+            "Memory leaked as not all network endpoints were shut down");
   }
   gpr_mu_destroy(&g_endpoint_mutex);
 }
diff --git a/src/core/lib/iomgr/resource_quota.c b/src/core/lib/iomgr/resource_quota.c
index e39cf28e35..8a06443d58 100644
--- a/src/core/lib/iomgr/resource_quota.c
+++ b/src/core/lib/iomgr/resource_quota.c
@@ -715,3 +715,10 @@ void grpc_resource_user_alloc_slices(
   grpc_resource_user_alloc(exec_ctx, slice_allocator->resource_user,
                            count * length, &slice_allocator->on_allocated);
 }
+
+gpr_slice grpc_resource_user_slice_malloc(grpc_exec_ctx *exec_ctx,
+                                          grpc_resource_user *resource_user,
+                                          size_t size) {
+  grpc_resource_user_alloc(exec_ctx, resource_user, size, NULL);
+  return ru_slice_create(resource_user, size);
+}
diff --git a/src/core/lib/iomgr/resource_quota.h b/src/core/lib/iomgr/resource_quota.h
index 6dfac55f88..da68f21a2c 100644
--- a/src/core/lib/iomgr/resource_quota.h
+++ b/src/core/lib/iomgr/resource_quota.h
@@ -221,4 +221,9 @@ void grpc_resource_user_alloc_slices(
     grpc_resource_user_slice_allocator *slice_allocator, size_t length,
     size_t count, gpr_slice_buffer *dest);
 
+/* Allocate one slice of length \a size synchronously. */
+gpr_slice grpc_resource_user_slice_malloc(grpc_exec_ctx *exec_ctx,
+                                          grpc_resource_user *resource_user,
+                                          size_t size);
+
 #endif /* GRPC_CORE_LIB_IOMGR_RESOURCE_QUOTA_H */
diff --git a/src/core/lib/iomgr/tcp_client_uv.c b/src/core/lib/iomgr/tcp_client_uv.c
index 6274667042..b07f9ceffa 100644
--- a/src/core/lib/iomgr/tcp_client_uv.c
+++ b/src/core/lib/iomgr/tcp_client_uv.c
@@ -54,9 +54,12 @@ typedef struct grpc_uv_tcp_connect {
   grpc_endpoint **endpoint;
   int refs;
   char *addr_name;
+  grpc_resource_quota *resource_quota;
 } grpc_uv_tcp_connect;
 
-static void uv_tcp_connect_cleanup(grpc_uv_tcp_connect *connect) {
+static void uv_tcp_connect_cleanup(grpc_exec_ctx *exec_ctx,
+                                   grpc_uv_tcp_connect *connect) {
+  grpc_resource_quota_internal_unref(exec_ctx, connect->resource_quota);
   gpr_free(connect);
 }
 
@@ -74,7 +77,7 @@ static void uv_tc_on_alarm(grpc_exec_ctx *exec_ctx, void *acp,
   }
   done = (--connect->refs == 0);
   if (done) {
-    uv_tcp_connect_cleanup(connect);
+    uv_tcp_connect_cleanup(exec_ctx, connect);
   }
 }
 
@@ -86,8 +89,8 @@ static void uv_tc_on_connect(uv_connect_t *req, int status) {
   grpc_closure *closure = connect->closure;
   grpc_timer_cancel(&exec_ctx, &connect->alarm);
   if (status == 0) {
-    *connect->endpoint =
-        grpc_tcp_create(connect->tcp_handle, connect->addr_name);
+    *connect->endpoint = grpc_tcp_create(
+        connect->tcp_handle, connect->resource_quota, connect->addr_name);
   } else {
     error = GRPC_ERROR_CREATE("Failed to connect to remote host");
     error = grpc_error_set_int(error, GRPC_ERROR_INT_ERRNO, -status);
@@ -105,7 +108,7 @@ static void uv_tc_on_connect(uv_connect_t *req, int status) {
   }
   done = (--connect->refs == 0);
   if (done) {
-    uv_tcp_connect_cleanup(connect);
+    uv_tcp_connect_cleanup(&exec_ctx, connect);
   }
   grpc_exec_ctx_sched(&exec_ctx, closure, error, NULL);
   grpc_exec_ctx_finish(&exec_ctx);
@@ -114,16 +117,31 @@ static void uv_tc_on_connect(uv_connect_t *req, int status) {
 static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
                                     grpc_closure *closure, grpc_endpoint **ep,
                                     grpc_pollset_set *interested_parties,
+                                    const grpc_channel_args *channel_args,
                                     const grpc_resolved_address *resolved_addr,
                                     gpr_timespec deadline) {
   grpc_uv_tcp_connect *connect;
+  grpc_resource_quota *resource_quota = grpc_resource_quota_create(NULL);
+  (void)channel_args;
   (void)interested_parties;
+
+  if (channel_args != NULL) {
+    for (size_t i = 0; i < channel_args->num_args; i++) {
+      if (0 == strcmp(channel_args->args[i].key, GRPC_ARG_RESOURCE_QUOTA)) {
+        grpc_resource_quota_internal_unref(exec_ctx, resource_quota);
+        resource_quota = grpc_resource_quota_internal_ref(
+            channel_args->args[i].value.pointer.p);
+      }
+    }
+  }
+
   connect = gpr_malloc(sizeof(grpc_uv_tcp_connect));
   memset(connect, 0, sizeof(grpc_uv_tcp_connect));
   connect->closure = closure;
   connect->endpoint = ep;
   connect->tcp_handle = gpr_malloc(sizeof(uv_tcp_t));
   connect->addr_name = grpc_sockaddr_to_uri(resolved_addr);
+  connect->resource_quota = resource_quota;
   uv_tcp_init(uv_default_loop(), connect->tcp_handle);
   connect->connect_req.data = connect;
   // TODO(murgatroid99): figure out what the return value here means
@@ -138,16 +156,18 @@ static void tcp_client_connect_impl(grpc_exec_ctx *exec_ctx,
 // overridden by api_fuzzer.c
 void (*grpc_tcp_client_connect_impl)(
     grpc_exec_ctx *exec_ctx, grpc_closure *closure, grpc_endpoint **ep,
-    grpc_pollset_set *interested_parties, const grpc_resolved_address *addr,
+    grpc_pollset_set *interested_parties, const grpc_channel_args *channel_args,
+    const grpc_resolved_address *addr,
     gpr_timespec deadline) = tcp_client_connect_impl;
 
 void grpc_tcp_client_connect(grpc_exec_ctx *exec_ctx, grpc_closure *closure,
                              grpc_endpoint **ep,
                              grpc_pollset_set *interested_parties,
+                             const grpc_channel_args *channel_args,
                              const grpc_resolved_address *addr,
                              gpr_timespec deadline) {
-  grpc_tcp_client_connect_impl(exec_ctx, closure, ep, interested_parties, addr,
-                               deadline);
+  grpc_tcp_client_connect_impl(exec_ctx, closure, ep, interested_parties,
+                               channel_args, addr, deadline);
 }
 
 #endif /* GRPC_UV */
diff --git a/src/core/lib/iomgr/tcp_server_posix.c b/src/core/lib/iomgr/tcp_server_posix.c
index b6fc1e4ca2..7e2fb0f1f9 100644
--- a/src/core/lib/iomgr/tcp_server_posix.c
+++ b/src/core/lib/iomgr/tcp_server_posix.c
@@ -657,41 +657,46 @@ done:
   }
 }
 
+/* Return listener at port_index or NULL. Should only be called with s->mu
+   locked. */
+static grpc_tcp_listener *get_port_index(grpc_tcp_server *s,
+                                         unsigned port_index) {
+  unsigned num_ports = 0;
+  grpc_tcp_listener *sp;
+  for (sp = s->head; sp; sp = sp->next) {
+    if (!sp->is_sibling) {
+      if (++num_ports > port_index) {
+        return sp;
+      }
+    }
+  }
+  return NULL;
+}
+
 unsigned grpc_tcp_server_port_fd_count(grpc_tcp_server *s,
                                        unsigned port_index) {
   unsigned num_fds = 0;
-  grpc_tcp_listener *sp;
   gpr_mu_lock(&s->mu);
-  for (sp = s->head; sp && port_index != 0; sp = sp->next) {
-    if (!sp->is_sibling) {
-      --port_index;
-    }
+  grpc_tcp_listener *sp = get_port_index(s, port_index);
+  for (; sp; sp = sp->sibling) {
+    ++num_fds;
   }
-  for (; sp; sp = sp->sibling, ++num_fds)
-    ;
   gpr_mu_unlock(&s->mu);
   return num_fds;
 }
 
 int grpc_tcp_server_port_fd(grpc_tcp_server *s, unsigned port_index,
                             unsigned fd_index) {
-  grpc_tcp_listener *sp;
-  int fd;
   gpr_mu_lock(&s->mu);
-  for (sp = s->head; sp && port_index != 0; sp = sp->next) {
-    if (!sp->is_sibling) {
-      --port_index;
+  grpc_tcp_listener *sp = get_port_index(s, port_index);
+  for (; sp; sp = sp->sibling, --fd_index) {
+    if (fd_index == 0) {
+      gpr_mu_unlock(&s->mu);
+      return sp->fd;
     }
   }
-  for (; sp && fd_index != 0; sp = sp->sibling, --fd_index)
-    ;
-  if (sp) {
-    fd = sp->fd;
-  } else {
-    fd = -1;
-  }
   gpr_mu_unlock(&s->mu);
-  return fd;
+  return -1;
 }
 
 void grpc_tcp_server_start(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s,
diff --git a/src/core/lib/iomgr/tcp_server_uv.c b/src/core/lib/iomgr/tcp_server_uv.c
index 73e4db3d65..b5b9b92a20 100644
--- a/src/core/lib/iomgr/tcp_server_uv.c
+++ b/src/core/lib/iomgr/tcp_server_uv.c
@@ -76,13 +76,30 @@ struct grpc_tcp_server {
 
   /* shutdown callback */
   grpc_closure *shutdown_complete;
+
+  grpc_resource_quota *resource_quota;
 };
 
-grpc_error *grpc_tcp_server_create(grpc_closure *shutdown_complete,
+grpc_error *grpc_tcp_server_create(grpc_exec_ctx *exec_ctx,
+                                   grpc_closure *shutdown_complete,
                                    const grpc_channel_args *args,
                                    grpc_tcp_server **server) {
   grpc_tcp_server *s = gpr_malloc(sizeof(grpc_tcp_server));
-  (void)args;
+  s->resource_quota = grpc_resource_quota_create(NULL);
+  for (size_t i = 0; i < (args == NULL ? 0 : args->num_args); i++) {
+    if (0 == strcmp(GRPC_ARG_RESOURCE_QUOTA, args->args[i].key)) {
+      if (args->args[i].type == GRPC_ARG_POINTER) {
+        grpc_resource_quota_internal_unref(exec_ctx, s->resource_quota);
+        s->resource_quota =
+            grpc_resource_quota_internal_ref(args->args[i].value.pointer.p);
+      } else {
+        grpc_resource_quota_internal_unref(exec_ctx, s->resource_quota);
+        gpr_free(s);
+        return GRPC_ERROR_CREATE(GRPC_ARG_RESOURCE_QUOTA
+                                 " must be a pointer to a buffer pool");
+      }
+    }
+  }
   gpr_ref_init(&s->refs, 1);
   s->on_accept_cb = NULL;
   s->on_accept_cb_arg = NULL;
@@ -119,6 +136,7 @@ static void finish_shutdown(grpc_exec_ctx *exec_ctx, grpc_tcp_server *s) {
     gpr_free(sp->handle);
     gpr_free(sp);
   }
+  grpc_resource_quota_internal_unref(exec_ctx, s->resource_quota);
   gpr_free(s);
 }
 
@@ -201,7 +219,7 @@ static void on_connect(uv_stream_t *server, int status) {
     } else {
       gpr_log(GPR_INFO, "uv_tcp_getpeername error: %s", uv_strerror(status));
     }
-    ep = grpc_tcp_create(client, peer_name_string);
+    ep = grpc_tcp_create(client, sp->server->resource_quota, peer_name_string);
     sp->server->on_accept_cb(&exec_ctx, sp->server->on_accept_cb_arg, ep, NULL,
                              &acceptor);
     grpc_exec_ctx_finish(&exec_ctx);
diff --git a/src/core/lib/iomgr/tcp_uv.c b/src/core/lib/iomgr/tcp_uv.c
index 3860fe3e9b..8e74c9e863 100644
--- a/src/core/lib/iomgr/tcp_uv.c
+++ b/src/core/lib/iomgr/tcp_uv.c
@@ -54,6 +54,9 @@ typedef struct {
   grpc_endpoint base;
   gpr_refcount refcount;
 
+  uv_write_t write_req;
+  uv_shutdown_t shutdown_req;
+
   uv_tcp_t *handle;
 
   grpc_closure *read_cb;
@@ -64,14 +67,23 @@ typedef struct {
   gpr_slice_buffer *write_slices;
   uv_buf_t *write_buffers;
 
+  grpc_resource_user resource_user;
+
   bool shutting_down;
+  bool resource_user_shutting_down;
+
   char *peer_string;
   grpc_pollset *pollset;
 } grpc_tcp;
 
 static void uv_close_callback(uv_handle_t *handle) { gpr_free(handle); }
 
-static void tcp_free(grpc_tcp *tcp) { gpr_free(tcp); }
+static void tcp_free(grpc_tcp *tcp) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
+  grpc_resource_user_destroy(&exec_ctx, &tcp->resource_user);
+  gpr_free(tcp);
+  grpc_exec_ctx_finish(&exec_ctx);
+}
 
 /*#define GRPC_TCP_REFCOUNT_DEBUG*/
 #ifdef GRPC_TCP_REFCOUNT_DEBUG
@@ -106,11 +118,14 @@ static void tcp_ref(grpc_tcp *tcp) { gpr_ref(&tcp->refcount); }
 
 static void alloc_uv_buf(uv_handle_t *handle, size_t suggested_size,
                          uv_buf_t *buf) {
+  grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
   grpc_tcp *tcp = handle->data;
   (void)suggested_size;
-  tcp->read_slice = gpr_slice_malloc(GRPC_TCP_DEFAULT_READ_SLICE_SIZE);
+  tcp->read_slice = grpc_resource_user_slice_malloc(
+      &exec_ctx, &tcp->resource_user, GRPC_TCP_DEFAULT_READ_SLICE_SIZE);
   buf->base = (char *)GPR_SLICE_START_PTR(tcp->read_slice);
   buf->len = GPR_SLICE_LENGTH(tcp->read_slice);
+  grpc_exec_ctx_finish(&exec_ctx);
 }
 
 static void read_callback(uv_stream_t *stream, ssize_t nread,
@@ -198,7 +213,8 @@ static void write_callback(uv_write_t *req, int status) {
     gpr_log(GPR_DEBUG, "write complete on %p: error=%s", tcp, str);
   }
   gpr_free(tcp->write_buffers);
-  gpr_free(req);
+  grpc_resource_user_free(&exec_ctx, &tcp->resource_user,
+                          sizeof(uv_buf_t) * tcp->write_slices->count);
   grpc_exec_ctx_sched(&exec_ctx, cb, error, NULL);
   grpc_exec_ctx_finish(&exec_ctx);
 }
@@ -243,12 +259,15 @@ static void uv_endpoint_write(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   tcp->write_cb = cb;
   buffer_count = (unsigned int)tcp->write_slices->count;
   buffers = gpr_malloc(sizeof(uv_buf_t) * buffer_count);
+  grpc_resource_user_alloc(exec_ctx, &tcp->resource_user,
+                           sizeof(uv_buf_t) * buffer_count, NULL);
   for (i = 0; i < buffer_count; i++) {
     slice = &tcp->write_slices->slices[i];
     buffers[i].base = (char *)GPR_SLICE_START_PTR(*slice);
     buffers[i].len = GPR_SLICE_LENGTH(*slice);
   }
-  write_req = gpr_malloc(sizeof(uv_write_t));
+  tcp->write_buffers = buffers;
+  write_req = &tcp->write_req;
   write_req->data = tcp;
   TCP_REF(tcp, "write");
   // TODO(murgatroid99): figure out what the return value here means
@@ -274,13 +293,29 @@ static void uv_add_to_pollset_set(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep,
   (void)pollset;
 }
 
-static void shutdown_callback(uv_shutdown_t *req, int status) { gpr_free(req); }
+static void shutdown_callback(uv_shutdown_t *req, int status) {}
+
+static void resource_user_shutdown_done(grpc_exec_ctx *exec_ctx, void *arg,
+                                        grpc_error *error) {
+  TCP_UNREF(arg, "resource_user");
+}
+
+static void uv_resource_user_maybe_shutdown(grpc_exec_ctx *exec_ctx,
+                                            grpc_tcp *tcp) {
+  if (!tcp->resource_user_shutting_down) {
+    tcp->resource_user_shutting_down = true;
+    TCP_REF(tcp, "resource_user");
+    grpc_resource_user_shutdown(
+        exec_ctx, &tcp->resource_user,
+        grpc_closure_create(resource_user_shutdown_done, tcp));
+  }
+}
 
 static void uv_endpoint_shutdown(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep) {
   grpc_tcp *tcp = (grpc_tcp *)ep;
   if (!tcp->shutting_down) {
     tcp->shutting_down = true;
-    uv_shutdown_t *req = gpr_malloc(sizeof(uv_shutdown_t));
+    uv_shutdown_t *req = &tcp->shutdown_req;
     uv_shutdown(req, (uv_stream_t *)tcp->handle, shutdown_callback);
   }
 }
@@ -289,6 +324,7 @@ static void uv_destroy(grpc_exec_ctx *exec_ctx, grpc_endpoint *ep) {
   grpc_network_status_unregister_endpoint(ep);
   grpc_tcp *tcp = (grpc_tcp *)ep;
   uv_close((uv_handle_t *)tcp->handle, uv_close_callback);
+  uv_resource_user_maybe_shutdown(exec_ctx, tcp);
   TCP_UNREF(tcp, "destroy");
 }
 
@@ -297,18 +333,21 @@ static char *uv_get_peer(grpc_endpoint *ep) {
   return gpr_strdup(tcp->peer_string);
 }
 
+static grpc_resource_user *uv_get_resource_user(grpc_endpoint *ep) {
+  grpc_tcp *tcp = (grpc_tcp *)ep;
+  return &tcp->resource_user;
+}
+
 static grpc_workqueue *uv_get_workqueue(grpc_endpoint *ep) { return NULL; }
 
-static grpc_endpoint_vtable vtable = {uv_endpoint_read,
-                                      uv_endpoint_write,
-                                      uv_get_workqueue,
-                                      uv_add_to_pollset,
-                                      uv_add_to_pollset_set,
-                                      uv_endpoint_shutdown,
-                                      uv_destroy,
-                                      uv_get_peer};
+static grpc_endpoint_vtable vtable = {
+    uv_endpoint_read,  uv_endpoint_write,     uv_get_workqueue,
+    uv_add_to_pollset, uv_add_to_pollset_set, uv_endpoint_shutdown,
+    uv_destroy,        uv_get_resource_user,  uv_get_peer};
 
-grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle, char *peer_string) {
+grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle,
+                               grpc_resource_quota *resource_quota,
+                               char *peer_string) {
   grpc_tcp *tcp = (grpc_tcp *)gpr_malloc(sizeof(grpc_tcp));
 
   if (grpc_tcp_trace) {
@@ -325,6 +364,8 @@ grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle, char *peer_string) {
   gpr_ref_init(&tcp->refcount, 1);
   tcp->peer_string = gpr_strdup(peer_string);
   tcp->shutting_down = false;
+  tcp->resource_user_shutting_down = false;
+  grpc_resource_user_init(&tcp->resource_user, resource_quota, peer_string);
   /* Tell network status tracking code about the new endpoint */
   grpc_network_status_register_endpoint(&tcp->base);
 
diff --git a/src/core/lib/iomgr/tcp_uv.h b/src/core/lib/iomgr/tcp_uv.h
index eed41151ea..970fcafe4a 100644
--- a/src/core/lib/iomgr/tcp_uv.h
+++ b/src/core/lib/iomgr/tcp_uv.h
@@ -52,6 +52,8 @@ extern int grpc_tcp_trace;
 
 #define GRPC_TCP_DEFAULT_READ_SLICE_SIZE 8192
 
-grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle, char *peer_string);
+grpc_endpoint *grpc_tcp_create(uv_tcp_t *handle,
+                               grpc_resource_quota *resource_quota,
+                               char *peer_string);
 
 #endif /* GRPC_CORE_LIB_IOMGR_TCP_UV_H */
diff --git a/src/core/lib/security/transport/security_connector.c b/src/core/lib/security/transport/security_connector.c
index 0eca46eb52..ebf72a3abb 100644
--- a/src/core/lib/security/transport/security_connector.c
+++ b/src/core/lib/security/transport/security_connector.c
@@ -210,11 +210,11 @@ void grpc_security_connector_unref(grpc_security_connector *sc) {
 }
 
 static void connector_pointer_arg_destroy(void *p) {
-  GRPC_SECURITY_CONNECTOR_UNREF(p, "connector_pointer_arg");
+  GRPC_SECURITY_CONNECTOR_UNREF(p, "connector_pointer_arg_destroy");
 }
 
 static void *connector_pointer_arg_copy(void *p) {
-  return GRPC_SECURITY_CONNECTOR_REF(p, "connector_pointer_arg");
+  return GRPC_SECURITY_CONNECTOR_REF(p, "connector_pointer_arg_copy");
 }
 
 static int connector_pointer_cmp(void *a, void *b) { return GPR_ICMP(a, b); }
diff --git a/src/core/lib/transport/pid_controller.c b/src/core/lib/transport/pid_controller.c
new file mode 100644
index 0000000000..3cef225d4b
--- /dev/null
+++ b/src/core/lib/transport/pid_controller.c
@@ -0,0 +1,57 @@
+/*
+ *
+ * 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/transport/pid_controller.h"
+
+void grpc_pid_controller_init(grpc_pid_controller *pid_controller,
+                              double gain_p, double gain_i, double gain_d) {
+  pid_controller->gain_p = gain_p;
+  pid_controller->gain_i = gain_i;
+  pid_controller->gain_d = gain_d;
+  grpc_pid_controller_reset(pid_controller);
+}
+
+void grpc_pid_controller_reset(grpc_pid_controller *pid_controller) {
+  pid_controller->last_error = 0.0;
+  pid_controller->error_integral = 0.0;
+}
+
+double grpc_pid_controller_update(grpc_pid_controller *pid_controller,
+                                  double error, double dt) {
+  pid_controller->error_integral += error * dt;
+  double diff_error = (error - pid_controller->last_error) / dt;
+  pid_controller->last_error = error;
+  return dt * (pid_controller->gain_p * error +
+               pid_controller->gain_i * pid_controller->error_integral +
+               pid_controller->gain_d * diff_error);
+}
diff --git a/src/core/lib/transport/pid_controller.h b/src/core/lib/transport/pid_controller.h
new file mode 100644
index 0000000000..059b5b0834
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+/*
+ *
+ * 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_TRANSPORT_PID_CONTROLLER_H
+#define GRPC_CORE_LIB_TRANSPORT_PID_CONTROLLER_H
+
+/* \file Simple PID controller.
+   Implements a proportional-integral-derivative controller.
+   Used when we want to iteratively control a variable to converge some other
+   observed value to a 'set-point'.
+   Gains can be set to adjust sensitivity to current error (p), the integral
+   of error (i), and the derivative of error (d). */
+
+typedef struct {
+  double gain_p;
+  double gain_i;
+  double gain_d;
+  double last_error;
+  double error_integral;
+} grpc_pid_controller;
+
+/** Initialize the controller */
+void grpc_pid_controller_init(grpc_pid_controller *pid_controller,
+                              double gain_p, double gain_i, double gain_d);
+
+/** Reset the controller: useful when things have changed significantly */
+void grpc_pid_controller_reset(grpc_pid_controller *pid_controller);
+
+/** Update the controller: given a current error estimate, and the time since
+    the last update, returns a delta to the control value */
+double grpc_pid_controller_update(grpc_pid_controller *pid_controller,
+                                  double error, double dt);
+
+#endif