19 files changed, 179 insertions, 5 deletions
diff --git a/src/core/lib/iomgr/combiner.cc b/src/core/lib/iomgr/combiner.cc
index 7c0062eb4e..402f8904ea 100644
--- a/src/core/lib/iomgr/combiner.cc
+++ b/src/core/lib/iomgr/combiner.cc
@@ -29,6 +29,7 @@
 
 #include "src/core/lib/debug/stats.h"
 #include "src/core/lib/iomgr/executor.h"
+#include "src/core/lib/iomgr/iomgr.h"
 #include "src/core/lib/profiling/timers.h"
 
 grpc_core::DebugOnlyTraceFlag grpc_combiner_trace(false, "combiner");
@@ -228,8 +229,14 @@ bool grpc_combiner_continue_exec_ctx() {
                               grpc_core::ExecCtx::Get()->IsReadyToFinish(),
                               lock->time_to_execute_final_list));
 
+  // offload only if all the following conditions are true:
+  // 1. the combiner is contended and has more than one closure to execute
+  // 2. the current execution context needs to finish as soon as possible
+  // 3. the DEFAULT executor is threaded
+  // 4. the current thread is not a worker for any background poller
   if (contended && grpc_core::ExecCtx::Get()->IsReadyToFinish() &&
-      grpc_executor_is_threaded()) {
+      grpc_executor_is_threaded() &&
+      !grpc_iomgr_is_any_background_poller_thread()) {
     GPR_TIMER_MARK("offload_from_finished_exec_ctx", 0);
     // this execution context wants to move on: schedule remaining work to be
     // picked up on the executor
diff --git a/src/core/lib/iomgr/ev_epoll1_linux.cc b/src/core/lib/iomgr/ev_epoll1_linux.cc
index 4b8c891e9b..9eb4c089d8 100644
--- a/src/core/lib/iomgr/ev_epoll1_linux.cc
+++ b/src/core/lib/iomgr/ev_epoll1_linux.cc
@@ -1242,6 +1242,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static bool is_any_background_poller_thread(void) { return false; }
+
 static void shutdown_background_closure(void) {}
 
 static void shutdown_engine(void) {
@@ -1287,6 +1289,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    is_any_background_poller_thread,
     shutdown_background_closure,
     shutdown_engine,
 };
diff --git a/src/core/lib/iomgr/ev_epollex_linux.cc b/src/core/lib/iomgr/ev_epollex_linux.cc
index 7a4870db78..0a0891013a 100644
--- a/src/core/lib/iomgr/ev_epollex_linux.cc
+++ b/src/core/lib/iomgr/ev_epollex_linux.cc
@@ -1604,6 +1604,8 @@ static void pollset_set_del_pollset_set(grpc_pollset_set* bag,
  * Event engine binding
  */
 
+static bool is_any_background_poller_thread(void) { return false; }
+
 static void shutdown_background_closure(void) {}
 
 static void shutdown_engine(void) {
@@ -1644,6 +1646,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    is_any_background_poller_thread,
     shutdown_background_closure,
     shutdown_engine,
 };
diff --git a/src/core/lib/iomgr/ev_poll_posix.cc b/src/core/lib/iomgr/ev_poll_posix.cc
index 67cbfbbd02..c479206410 100644
--- a/src/core/lib/iomgr/ev_poll_posix.cc
+++ b/src/core/lib/iomgr/ev_poll_posix.cc
@@ -1782,6 +1782,8 @@ static void global_cv_fd_table_shutdown() {
  * event engine binding
  */
 
+static bool is_any_background_poller_thread(void) { return false; }
+
 static void shutdown_background_closure(void) {}
 
 static void shutdown_engine(void) {
@@ -1828,6 +1830,7 @@ static const grpc_event_engine_vtable vtable = {
     pollset_set_add_fd,
     pollset_set_del_fd,
 
+    is_any_background_poller_thread,
     shutdown_background_closure,
     shutdown_engine,
 };
diff --git a/src/core/lib/iomgr/ev_posix.cc b/src/core/lib/iomgr/ev_posix.cc
index 32d1b6c43e..fb2e70eee4 100644
--- a/src/core/lib/iomgr/ev_posix.cc
+++ b/src/core/lib/iomgr/ev_posix.cc
@@ -399,6 +399,10 @@ void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd) {
   g_event_engine->pollset_set_del_fd(pollset_set, fd);
 }
 
+bool grpc_is_any_background_poller_thread(void) {
+  return g_event_engine->is_any_background_poller_thread();
+}
+
 void grpc_shutdown_background_closure(void) {
   g_event_engine->shutdown_background_closure();
 }
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index 812c7a0f0f..94ac9fdba6 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -80,6 +80,7 @@ typedef struct grpc_event_engine_vtable {
   void (*pollset_set_add_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
   void (*pollset_set_del_fd)(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+  bool (*is_any_background_poller_thread)(void);
   void (*shutdown_background_closure)(void);
   void (*shutdown_engine)(void);
 } grpc_event_engine_vtable;
@@ -181,6 +182,9 @@ void grpc_pollset_add_fd(grpc_pollset* pollset, struct grpc_fd* fd);
 void grpc_pollset_set_add_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 void grpc_pollset_set_del_fd(grpc_pollset_set* pollset_set, grpc_fd* fd);
 
+/* Returns true if the caller is a worker thread for any background poller. */
+bool grpc_is_any_background_poller_thread();
+
 /* Shut down all the closures registered in the background poller. */
 void grpc_shutdown_background_closure();
 
diff --git a/src/core/lib/iomgr/grpc_if_nametoindex.h b/src/core/lib/iomgr/grpc_if_nametoindex.h
new file mode 100644
index 0000000000..ed9612dcb9
--- /dev/null
+++ b/src/core/lib/iomgr/grpc_if_nametoindex.h
@@ -0,0 +1,30 @@
+/*
+ *
+ * Copyright 2015 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_GRPC_IF_NAMETOINDEX_H
+#define GRPC_CORE_LIB_IOMGR_GRPC_IF_NAMETOINDEX_H
+
+#include <grpc/support/port_platform.h>
+
+#include <stddef.h>
+
+/* Returns the interface index corresponding to the interface "name" provided.
+ * Returns non-zero upon success, and zero upon failure. */
+uint32_t grpc_if_nametoindex(char* name);
+
+#endif /* GRPC_CORE_LIB_IOMGR_GRPC_IF_NAMETOINDEX_H */
diff --git a/src/core/lib/iomgr/grpc_if_nametoindex_posix.cc b/src/core/lib/iomgr/grpc_if_nametoindex_posix.cc
new file mode 100644
index 0000000000..f1ba20dcec
--- /dev/null
+++ b/src/core/lib/iomgr/grpc_if_nametoindex_posix.cc
@@ -0,0 +1,42 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/lib/iomgr/port.h"
+
+#if GRPC_IF_NAMETOINDEX == 1 && defined(GRPC_POSIX_SOCKET_IF_NAMETOINDEX)
+
+#include "src/core/lib/iomgr/grpc_if_nametoindex.h"
+
+#include <errno.h>
+#include <net/if.h>
+
+#include <grpc/support/log.h>
+
+uint32_t grpc_if_nametoindex(char* name) {
+  uint32_t out = if_nametoindex(name);
+  if (out == 0) {
+    gpr_log(GPR_DEBUG, "if_nametoindex failed for name %s. errno %d", name,
+            errno);
+  }
+  return out;
+}
+
+#endif /* GRPC_IF_NAMETOINDEX == 1 && \
+          defined(GRPC_POSIX_SOCKET_IF_NAMETOINDEX) */
diff --git a/src/core/lib/iomgr/grpc_if_nametoindex_unsupported.cc b/src/core/lib/iomgr/grpc_if_nametoindex_unsupported.cc
new file mode 100644
index 0000000000..08644cccf3
--- /dev/null
+++ b/src/core/lib/iomgr/grpc_if_nametoindex_unsupported.cc
@@ -0,0 +1,38 @@
+/*
+ *
+ * Copyright 2016 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/lib/iomgr/port.h"
+
+#if GRPC_IF_NAMETOINDEX == 0 || !defined(GRPC_POSIX_SOCKET_IF_NAMETOINDEX)
+
+#include "src/core/lib/iomgr/grpc_if_nametoindex.h"
+
+#include <grpc/support/log.h>
+
+uint32_t grpc_if_nametoindex(char* name) {
+  gpr_log(GPR_DEBUG,
+          "Not attempting to convert interface name %s to index for current "
+          "platform.",
+          name);
+  return 0;
+}
+
+#endif /* GRPC_IF_NAMETOINDEX == 0 || \
+          !defined(GRPC_POSIX_SOCKET_IF_NAMETOINDEX) */
diff --git a/src/core/lib/iomgr/iomgr.cc b/src/core/lib/iomgr/iomgr.cc
index eb29973514..a492146857 100644
--- a/src/core/lib/iomgr/iomgr.cc
+++ b/src/core/lib/iomgr/iomgr.cc
@@ -161,6 +161,10 @@ void grpc_iomgr_shutdown_background_closure() {
   grpc_iomgr_platform_shutdown_background_closure();
 }
 
+bool grpc_iomgr_is_any_background_poller_thread() {
+  return grpc_iomgr_platform_is_any_background_poller_thread();
+}
+
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name) {
   obj->name = gpr_strdup(name);
   gpr_mu_lock(&g_mu);
diff --git a/src/core/lib/iomgr/iomgr.h b/src/core/lib/iomgr/iomgr.h
index 8ea9289e06..6261aa550c 100644
--- a/src/core/lib/iomgr/iomgr.h
+++ b/src/core/lib/iomgr/iomgr.h
@@ -39,6 +39,9 @@ void grpc_iomgr_shutdown();
  * background poller. */
 void grpc_iomgr_shutdown_background_closure();
 
+/** Returns true if the caller is a worker thread for any background poller. */
+bool grpc_iomgr_is_any_background_poller_thread();
+
 /* Exposed only for testing */
 size_t grpc_iomgr_count_objects_for_testing();
 
diff --git a/src/core/lib/iomgr/iomgr_custom.cc b/src/core/lib/iomgr/iomgr_custom.cc
index 4b112c9097..e1cd8f7310 100644
--- a/src/core/lib/iomgr/iomgr_custom.cc
+++ b/src/core/lib/iomgr/iomgr_custom.cc
@@ -41,10 +41,14 @@ static void iomgr_platform_init(void) {
 static void iomgr_platform_flush(void) {}
 static void iomgr_platform_shutdown(void) { grpc_pollset_global_shutdown(); }
 static void iomgr_platform_shutdown_background_closure(void) {}
+static bool iomgr_platform_is_any_background_poller_thread(void) {
+  return false;
+}
 
 static grpc_iomgr_platform_vtable vtable = {
     iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
-    iomgr_platform_shutdown_background_closure};
+    iomgr_platform_shutdown_background_closure,
+    iomgr_platform_is_any_background_poller_thread};
 
 void grpc_custom_iomgr_init(grpc_socket_vtable* socket,
                             grpc_custom_resolver_vtable* resolver,
diff --git a/src/core/lib/iomgr/iomgr_internal.cc b/src/core/lib/iomgr/iomgr_internal.cc
index b6c9211865..e68b1cf581 100644
--- a/src/core/lib/iomgr/iomgr_internal.cc
+++ b/src/core/lib/iomgr/iomgr_internal.cc
@@ -45,3 +45,7 @@ void grpc_iomgr_platform_shutdown() { iomgr_platform_vtable->shutdown(); }
 void grpc_iomgr_platform_shutdown_background_closure() {
   iomgr_platform_vtable->shutdown_background_closure();
 }
+
+bool grpc_iomgr_platform_is_any_background_poller_thread() {
+  return iomgr_platform_vtable->is_any_background_poller_thread();
+}
diff --git a/src/core/lib/iomgr/iomgr_internal.h b/src/core/lib/iomgr/iomgr_internal.h
index bca7409907..2250ad9a18 100644
--- a/src/core/lib/iomgr/iomgr_internal.h
+++ b/src/core/lib/iomgr/iomgr_internal.h
@@ -36,6 +36,7 @@ typedef struct grpc_iomgr_platform_vtable {
   void (*flush)(void);
   void (*shutdown)(void);
   void (*shutdown_background_closure)(void);
+  bool (*is_any_background_poller_thread)(void);
 } grpc_iomgr_platform_vtable;
 
 void grpc_iomgr_register_object(grpc_iomgr_object* obj, const char* name);
@@ -56,6 +57,9 @@ void grpc_iomgr_platform_shutdown(void);
 /** shut down all the closures registered in the background poller */
 void grpc_iomgr_platform_shutdown_background_closure(void);
 
+/** return true is the caller is a worker thread for any background poller */
+bool grpc_iomgr_platform_is_any_background_poller_thread(void);
+
 bool grpc_iomgr_abort_on_leaks(void);
 
 #endif /* GRPC_CORE_LIB_IOMGR_IOMGR_INTERNAL_H */
diff --git a/src/core/lib/iomgr/iomgr_posix.cc b/src/core/lib/iomgr/iomgr_posix.cc
index 9386adf060..278c8de688 100644
--- a/src/core/lib/iomgr/iomgr_posix.cc
+++ b/src/core/lib/iomgr/iomgr_posix.cc
@@ -55,9 +55,14 @@ static void iomgr_platform_shutdown_background_closure(void) {
   grpc_shutdown_background_closure();
 }
 
+static bool iomgr_platform_is_any_background_poller_thread(void) {
+  return grpc_is_any_background_poller_thread();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
     iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
-    iomgr_platform_shutdown_background_closure};
+    iomgr_platform_shutdown_background_closure,
+    iomgr_platform_is_any_background_poller_thread};
 
 void grpc_set_default_iomgr_platform() {
   grpc_set_tcp_client_impl(&grpc_posix_tcp_client_vtable);
diff --git a/src/core/lib/iomgr/iomgr_posix_cfstream.cc b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
index 552ef4309c..462ac41fcd 100644
--- a/src/core/lib/iomgr/iomgr_posix_cfstream.cc
+++ b/src/core/lib/iomgr/iomgr_posix_cfstream.cc
@@ -58,9 +58,14 @@ static void iomgr_platform_shutdown_background_closure(void) {
   grpc_shutdown_background_closure();
 }
 
+static bool iomgr_platform_is_any_background_poller_thread(void) {
+  return grpc_is_any_background_poller_thread();
+}
+
 static grpc_iomgr_platform_vtable vtable = {
     iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
-    iomgr_platform_shutdown_background_closure};
+    iomgr_platform_shutdown_background_closure,
+    iomgr_platform_is_any_background_poller_thread};
 
 void grpc_set_default_iomgr_platform() {
   char* enable_cfstream = getenv(grpc_cfstream_env_var);
diff --git a/src/core/lib/iomgr/iomgr_windows.cc b/src/core/lib/iomgr/iomgr_windows.cc
index 24ef0dba7b..0579e16aa7 100644
--- a/src/core/lib/iomgr/iomgr_windows.cc
+++ b/src/core/lib/iomgr/iomgr_windows.cc
@@ -73,9 +73,14 @@ static void iomgr_platform_shutdown(void) {
 
 static void iomgr_platform_shutdown_background_closure(void) {}
 
+static bool iomgr_platform_is_any_background_poller_thread(void) {
+  return false;
+}
+
 static grpc_iomgr_platform_vtable vtable = {
     iomgr_platform_init, iomgr_platform_flush, iomgr_platform_shutdown,
-    iomgr_platform_shutdown_background_closure};
+    iomgr_platform_shutdown_background_closure,
+    iomgr_platform_is_any_background_poller_thread};
 
 void grpc_set_default_iomgr_platform() {
   grpc_set_tcp_client_impl(&grpc_windows_tcp_client_vtable);
diff --git a/src/core/lib/iomgr/port.h b/src/core/lib/iomgr/port.h
index c8046b21dc..7b6ca1bc0e 100644
--- a/src/core/lib/iomgr/port.h
+++ b/src/core/lib/iomgr/port.h
@@ -184,6 +184,7 @@
 #define GRPC_POSIX_SOCKET_EV_EPOLLEX 1
 #define GRPC_POSIX_SOCKET_EV_POLL 1
 #define GRPC_POSIX_SOCKET_EV_EPOLL1 1
+#define GRPC_POSIX_SOCKET_IF_NAMETOINDEX 1
 #define GRPC_POSIX_SOCKET_IOMGR 1
 #define GRPC_POSIX_SOCKET_RESOLVE_ADDRESS 1
 #define GRPC_POSIX_SOCKET_SOCKADDR 1
diff --git a/src/core/lib/surface/channel_init.h b/src/core/lib/surface/channel_init.h
index f01852473b..d17a721606 100644
--- a/src/core/lib/surface/channel_init.h
+++ b/src/core/lib/surface/channel_init.h
@@ -45,6 +45,11 @@ void grpc_channel_init_init(void);
 /// registration order (in the case of a tie).
 /// Stages are registered against one of the pre-determined channel stack
 /// types.
+/// If the channel stack type is GRPC_CLIENT_SUBCHANNEL, the caller should
+/// ensure that subchannels with different filter lists will always have
+/// different channel args. This requires setting a channel arg in case the
+/// registration function relies on some condition other than channel args to
+/// decide whether to add a filter or not.
 void grpc_channel_init_register_stage(grpc_channel_stack_type type,
                                       int priority,
                                       grpc_channel_init_stage stage_fn,