If we cant check timers due to contention, at least make sure we do a follow up check soon

src/core/client_config/subchannel.c

@@ -184,8 +184,8 @@ static void connection_destroy(grpc_exec_ctx *exec_ctx, void *arg,
   gpr_free(c);
 }
 
-void grpc_connected_subchannel_ref(
+void grpc_connected_subchannel_ref(grpc_connected_subchannel *c
-    grpc_connected_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+                                       GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   GRPC_CHANNEL_STACK_REF(CHANNEL_STACK_FROM_CONNECTION(c), REF_REASON);
 }
 
@@ -226,8 +226,8 @@ static gpr_atm ref_mutate(grpc_subchannel *c, gpr_atm delta,
   return old_val;
 }
 
-grpc_subchannel *grpc_subchannel_ref(
+grpc_subchannel *grpc_subchannel_ref(grpc_subchannel *c
-    grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+                                         GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
   old_refs = ref_mutate(c, (1 << INTERNAL_REF_BITS),
                         0 REF_MUTATE_PURPOSE("STRONG_REF"));
@@ -235,8 +235,8 @@ grpc_subchannel *grpc_subchannel_ref(
   return c;
 }
 
-grpc_subchannel *grpc_subchannel_weak_ref(
+grpc_subchannel *grpc_subchannel_weak_ref(grpc_subchannel *c
-    grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+                                              GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
   old_refs = ref_mutate(c, 1, 0 REF_MUTATE_PURPOSE("WEAK_REF"));
   GPR_ASSERT(old_refs != 0);
@@ -686,8 +686,8 @@ static void subchannel_call_destroy(grpc_exec_ctx *exec_ctx, void *call,
   GPR_TIMER_END("grpc_subchannel_call_unref.destroy", 0);
 }
 
-void grpc_subchannel_call_ref(
+void grpc_subchannel_call_ref(grpc_subchannel_call *c
-    grpc_subchannel_call *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
+                                  GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   GRPC_CALL_STACK_REF(SUBCHANNEL_CALL_TO_CALL_STACK(c), REF_REASON);
 }
 

src/core/iomgr/timer.c

@@ -330,6 +330,9 @@ static int run_some_expired_timers(grpc_exec_ctx *exec_ctx, gpr_timespec now,
 
     gpr_mu_unlock(&g_mu);
     gpr_mu_unlock(&g_checker_mu);
+  } else if (next != NULL) {
+    *next = gpr_time_min(
+        *next, gpr_time_add(now, gpr_time_from_millis(100, GPR_TIMESPAN)));
   }
 
   return (int)n;

src/core/iomgr/timer.h

@@ -96,7 +96,6 @@ void grpc_timer_cancel(grpc_exec_ctx *exec_ctx, grpc_timer *timer);
    *next is never guaranteed to be updated on any given execution; however,
    with high probability at least one thread in the system will see an update
    at any time slice. */
-
 bool grpc_timer_check(grpc_exec_ctx *exec_ctx, gpr_timespec now,
                       gpr_timespec *next);
 void grpc_timer_list_init(gpr_timespec now);

src/core/surface/completion_queue.c

@@ -86,7 +86,7 @@ struct grpc_completion_queue {
 #define POLLSET_FROM_CQ(cq) ((grpc_pollset *)(cq + 1))
 
 static gpr_mu g_freelist_mu;
-grpc_completion_queue *g_freelist;
+static grpc_completion_queue *g_freelist;
 
 static void on_pollset_shutdown_done(grpc_exec_ctx *exec_ctx, void *cc,
                                      bool success);

test/core/surface/concurrent_connectivity_test.c

@@ -1,3 +1,36 @@
+/*
+*
+* Copyright 2015-2016, 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 <stdio.h>
 
 #include <grpc/grpc.h>
@@ -24,9 +57,9 @@ void create_loop_destroy(void* actually_an_int) {
       grpc_connectivity_state state =
           grpc_channel_check_connectivity_state(chan, 1);
       grpc_channel_watch_connectivity_state(chan, state, later_time, cq, NULL);
-      GPR_ASSERT(grpc_completion_queue_next(
+      GPR_ASSERT(grpc_completion_queue_next(cq,
-                     cq, GRPC_TIMEOUT_SECONDS_TO_DEADLINE(3), NULL)
+                                            GRPC_TIMEOUT_SECONDS_TO_DEADLINE(3),
-                     .type == GRPC_OP_COMPLETE);
+                                            NULL).type == GRPC_OP_COMPLETE);
     }
     grpc_channel_destroy(channels[thread_index]);
     grpc_completion_queue_destroy(queues[thread_index]);

test/core/surface/lame_client_test.c

@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015-2016, Google Inc.
+ * Copyright 2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without