Merge pull request #11703 from yang-g/cq_shutdown

Allow adding events to cq after shutdown is called.

15 files changed, 108 insertions, 76 deletions

diff --git a/include/grpc/impl/codegen/grpc_types.h b/include/grpc/impl/codegen/grpc_types.h
index f1c457c027..bb3c90e303 100644
--- a/include/grpc/impl/codegen/grpc_types.h
+++ b/include/grpc/impl/codegen/grpc_types.h
@@ -333,7 +333,9 @@ typedef enum grpc_call_error {
   /** this batch of operations leads to more operations than allowed */
   GRPC_CALL_ERROR_BATCH_TOO_BIG,
   /** payload type requested is not the type registered */
-  GRPC_CALL_ERROR_PAYLOAD_TYPE_MISMATCH
+  GRPC_CALL_ERROR_PAYLOAD_TYPE_MISMATCH,
+  /** completion queue has been shutdown */
+  GRPC_CALL_ERROR_COMPLETION_QUEUE_SHUTDOWN
 } grpc_call_error;
 
 /** Default send/receive message size limits in bytes. -1 for unlimited. */
diff --git a/src/core/ext/filters/client_channel/channel_connectivity.c b/src/core/ext/filters/client_channel/channel_connectivity.c
index c3dca14305..b83c95275f 100644
--- a/src/core/ext/filters/client_channel/channel_connectivity.c
+++ b/src/core/ext/filters/client_channel/channel_connectivity.c
@@ -208,7 +208,7 @@ void grpc_channel_watch_connectivity_state(
       7, (channel, (int)last_observed_state, deadline.tv_sec, deadline.tv_nsec,
           (int)deadline.clock_type, cq, tag));
 
-  grpc_cq_begin_op(cq, tag);
+  GPR_ASSERT(grpc_cq_begin_op(cq, tag));
 
   gpr_mu_init(&w->mu);
   GRPC_CLOSURE_INIT(&w->on_complete, watch_complete, w,
diff --git a/src/core/lib/surface/alarm.c b/src/core/lib/surface/alarm.c
index ef8405cca8..55934964f3 100644
--- a/src/core/lib/surface/alarm.c
+++ b/src/core/lib/surface/alarm.c
@@ -18,6 +18,7 @@
 
 #include <grpc/grpc.h>
 #include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
 #include "src/core/lib/iomgr/timer.h"
 #include "src/core/lib/surface/completion_queue.h"
 
@@ -49,7 +50,7 @@ grpc_alarm *grpc_alarm_create(grpc_completion_queue *cq, gpr_timespec deadline,
   alarm->cq = cq;
   alarm->tag = tag;
 
-  grpc_cq_begin_op(cq, tag);
+  GPR_ASSERT(grpc_cq_begin_op(cq, tag));
   GRPC_CLOSURE_INIT(&alarm->on_alarm, alarm_cb, alarm,
                     grpc_schedule_on_exec_ctx);
   grpc_timer_init(&exec_ctx, &alarm->alarm,
diff --git a/src/core/lib/surface/call.c b/src/core/lib/surface/call.c
index 2365d27307..04613f17e3 100644
--- a/src/core/lib/surface/call.c
+++ b/src/core/lib/surface/call.c
@@ -1422,7 +1422,7 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
 
   if (nops == 0) {
     if (!is_notify_tag_closure) {
-      grpc_cq_begin_op(call->cq, notify_tag);
+      GPR_ASSERT(grpc_cq_begin_op(call->cq, notify_tag));
       grpc_cq_end_op(exec_ctx, call->cq, notify_tag, GRPC_ERROR_NONE,
                      free_no_op_completion, NULL,
                      gpr_malloc(sizeof(grpc_cq_completion)));
@@ -1723,7 +1723,7 @@ static grpc_call_error call_start_batch(grpc_exec_ctx *exec_ctx,
 
   GRPC_CALL_INTERNAL_REF(call, "completion");
   if (!is_notify_tag_closure) {
-    grpc_cq_begin_op(call->cq, notify_tag);
+    GPR_ASSERT(grpc_cq_begin_op(call->cq, notify_tag));
   }
   gpr_ref_init(&bctl->steps_to_complete, num_completion_callbacks_needed);
 
@@ -1844,6 +1844,8 @@ const char *grpc_call_error_to_string(grpc_call_error error) {
       return "GRPC_CALL_ERROR_PAYLOAD_TYPE_MISMATCH";
     case GRPC_CALL_ERROR_TOO_MANY_OPERATIONS:
       return "GRPC_CALL_ERROR_TOO_MANY_OPERATIONS";
+    case GRPC_CALL_ERROR_COMPLETION_QUEUE_SHUTDOWN:
+      return "GRPC_CALL_ERROR_COMPLETION_QUEUE_SHUTDOWN";
     case GRPC_CALL_OK:
       return "GRPC_CALL_OK";
   }
diff --git a/src/core/lib/surface/channel_ping.c b/src/core/lib/surface/channel_ping.c
index 80eb80af78..e85b308850 100644
--- a/src/core/lib/surface/channel_ping.c
+++ b/src/core/lib/surface/channel_ping.c
@@ -59,7 +59,7 @@ void grpc_channel_ping(grpc_channel *channel, grpc_completion_queue *cq,
   GRPC_CLOSURE_INIT(&pr->closure, ping_done, pr, grpc_schedule_on_exec_ctx);
   op->send_ping = &pr->closure;
   op->bind_pollset = grpc_cq_pollset(cq);
-  grpc_cq_begin_op(cq, tag);
+  GPR_ASSERT(grpc_cq_begin_op(cq, tag));
   top_elem->filter->start_transport_op(&exec_ctx, top_elem, op);
   grpc_exec_ctx_finish(&exec_ctx);
 }
diff --git a/src/core/lib/surface/completion_queue.c b/src/core/lib/surface/completion_queue.c
index 3851993c92..3d82a32e82 100644
--- a/src/core/lib/surface/completion_queue.c
+++ b/src/core/lib/surface/completion_queue.c
@@ -196,7 +196,7 @@ typedef struct cq_vtable {
   void (*init)(void *data);
   void (*shutdown)(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cq);
   void (*destroy)(void *data);
-  void (*begin_op)(grpc_completion_queue *cq, void *tag);
+  bool (*begin_op)(grpc_completion_queue *cq, void *tag);
   void (*end_op)(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cq, void *tag,
                  grpc_error *error,
                  void (*done)(grpc_exec_ctx *exec_ctx, void *done_arg,
@@ -288,8 +288,8 @@ static void cq_shutdown_next(grpc_exec_ctx *exec_ctx,
 static void cq_shutdown_pluck(grpc_exec_ctx *exec_ctx,
                               grpc_completion_queue *cq);
 
-static void cq_begin_op_for_next(grpc_completion_queue *cq, void *tag);
-static void cq_begin_op_for_pluck(grpc_completion_queue *cq, void *tag);
+static bool cq_begin_op_for_next(grpc_completion_queue *cq, void *tag);
+static bool cq_begin_op_for_pluck(grpc_completion_queue *cq, void *tag);
 
 static void cq_end_op_for_next(grpc_exec_ctx *exec_ctx,
                                grpc_completion_queue *cq, void *tag,
@@ -522,33 +522,6 @@ void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx,
   }
 }
 
-static void cq_begin_op_for_next(grpc_completion_queue *cq, void *tag) {
-  cq_next_data *cqd = DATA_FROM_CQ(cq);
-  GPR_ASSERT(!cqd->shutdown_called);
-  gpr_atm_no_barrier_fetch_add(&cqd->pending_events, 1);
-}
-
-static void cq_begin_op_for_pluck(grpc_completion_queue *cq, void *tag) {
-  cq_pluck_data *cqd = DATA_FROM_CQ(cq);
-  GPR_ASSERT(!cqd->shutdown_called);
-  gpr_ref(&cqd->pending_events);
-}
-
-void grpc_cq_begin_op(grpc_completion_queue *cq, void *tag) {
-#ifndef NDEBUG
-  gpr_mu_lock(cq->mu);
-  if (cq->outstanding_tag_count == cq->outstanding_tag_capacity) {
-    cq->outstanding_tag_capacity = GPR_MAX(4, 2 * cq->outstanding_tag_capacity);
-    cq->outstanding_tags =
-        gpr_realloc(cq->outstanding_tags, sizeof(*cq->outstanding_tags) *
-                                              cq->outstanding_tag_capacity);
-  }
-  cq->outstanding_tags[cq->outstanding_tag_count++] = tag;
-  gpr_mu_unlock(cq->mu);
-#endif
-  cq->vtable->begin_op(cq, tag);
-}
-
 #ifndef NDEBUG
 static void cq_check_tag(grpc_completion_queue *cq, void *tag, bool lock_cq) {
   int found = 0;
@@ -576,6 +549,41 @@ static void cq_check_tag(grpc_completion_queue *cq, void *tag, bool lock_cq) {
 static void cq_check_tag(grpc_completion_queue *cq, void *tag, bool lock_cq) {}
 #endif
 
+static bool cq_begin_op_for_next(grpc_completion_queue *cq, void *tag) {
+  cq_next_data *cqd = DATA_FROM_CQ(cq);
+  while (true) {
+    gpr_atm count = gpr_atm_no_barrier_load(&cqd->pending_events);
+    if (count == 0) {
+      return false;
+    } else if (gpr_atm_no_barrier_cas(&cqd->pending_events, count, count + 1)) {
+      break;
+    }
+  }
+  return true;
+}
+
+static bool cq_begin_op_for_pluck(grpc_completion_queue *cq, void *tag) {
+  cq_pluck_data *cqd = DATA_FROM_CQ(cq);
+  GPR_ASSERT(!cqd->shutdown_called);
+  gpr_ref(&cqd->pending_events);
+  return true;
+}
+
+bool grpc_cq_begin_op(grpc_completion_queue *cq, void *tag) {
+#ifndef NDEBUG
+  gpr_mu_lock(cq->mu);
+  if (cq->outstanding_tag_count == cq->outstanding_tag_capacity) {
+    cq->outstanding_tag_capacity = GPR_MAX(4, 2 * cq->outstanding_tag_capacity);
+    cq->outstanding_tags =
+        gpr_realloc(cq->outstanding_tags, sizeof(*cq->outstanding_tags) *
+                                              cq->outstanding_tag_capacity);
+  }
+  cq->outstanding_tags[cq->outstanding_tag_count++] = tag;
+  gpr_mu_unlock(cq->mu);
+#endif
+  return cq->vtable->begin_op(cq, tag);
+}
+
 /* Queue a GRPC_OP_COMPLETED operation to a completion queue (with a
  * completion
  * type of GRPC_CQ_NEXT) */
diff --git a/src/core/lib/surface/completion_queue.h b/src/core/lib/surface/completion_queue.h
index af44482513..69d144bd95 100644
--- a/src/core/lib/surface/completion_queue.h
+++ b/src/core/lib/surface/completion_queue.h
@@ -72,8 +72,9 @@ void grpc_cq_internal_unref(grpc_exec_ctx *exec_ctx, grpc_completion_queue *cc);
 
 /* Flag that an operation is beginning: the completion channel will not finish
    shutdown until a corrensponding grpc_cq_end_* call is made.
-   \a tag is currently used only in debug builds. */
-void grpc_cq_begin_op(grpc_completion_queue *cc, void *tag);
+   \a tag is currently used only in debug builds. Return true on success, and
+   false if completion_queue has been shutdown. */
+bool grpc_cq_begin_op(grpc_completion_queue *cc, void *tag);
 
 /* Queue a GRPC_OP_COMPLETED operation; tag must correspond to the tag passed to
    grpc_cq_begin_op */
diff --git a/src/core/lib/surface/server.c b/src/core/lib/surface/server.c
index fce7f8dca1..66dcc299aa 100644
--- a/src/core/lib/surface/server.c
+++ b/src/core/lib/surface/server.c
@@ -1259,7 +1259,7 @@ void grpc_server_shutdown_and_notify(grpc_server *server,
   }
 
   /* stay locked, and gather up some stuff to do */
-  grpc_cq_begin_op(cq, tag);
+  GPR_ASSERT(grpc_cq_begin_op(cq, tag));
   if (server->shutdown_published) {
     grpc_cq_end_op(&exec_ctx, cq, tag, GRPC_ERROR_NONE, done_published_shutdown,
                    NULL, gpr_malloc(sizeof(grpc_cq_completion)));
@@ -1446,7 +1446,11 @@ grpc_call_error grpc_server_request_call(
     error = GRPC_CALL_ERROR_NOT_SERVER_COMPLETION_QUEUE;
     goto done;
   }
-  grpc_cq_begin_op(cq_for_notification, tag);
+  if (grpc_cq_begin_op(cq_for_notification, tag) == false) {
+    gpr_free(rc);
+    error = GRPC_CALL_ERROR_COMPLETION_QUEUE_SHUTDOWN;
+    goto done;
+  }
   details->reserved = NULL;
   rc->cq_idx = cq_idx;
   rc->type = BATCH_CALL;
@@ -1496,7 +1500,11 @@ grpc_call_error grpc_server_request_registered_call(
     error = GRPC_CALL_ERROR_PAYLOAD_TYPE_MISMATCH;
     goto done;
   }
-  grpc_cq_begin_op(cq_for_notification, tag);
+  if (grpc_cq_begin_op(cq_for_notification, tag) == false) {
+    gpr_free(rc);
+    error = GRPC_CALL_ERROR_COMPLETION_QUEUE_SHUTDOWN;
+    goto done;
+  }
   rc->cq_idx = cq_idx;
   rc->type = REGISTERED_CALL;
   rc->server = server;
diff --git a/src/cpp/server/server_cc.cc b/src/cpp/server/server_cc.cc
index 92bacbe061..2483300cb1 100644
--- a/src/cpp/server/server_cc.cc
+++ b/src/cpp/server/server_cc.cc
@@ -151,19 +151,25 @@ class Server::SyncRequest final : public CompletionQueueTag {
     GPR_ASSERT(cq_ && !in_flight_);
     in_flight_ = true;
     if (tag_) {
-      GPR_ASSERT(GRPC_CALL_OK ==
-                 grpc_server_request_registered_call(
-                     server, tag_, &call_, &deadline_, &request_metadata_,
-                     has_request_payload_ ? &request_payload_ : nullptr, cq_,
-                     notify_cq, this));
+      if (GRPC_CALL_OK !=
+          grpc_server_request_registered_call(
+              server, tag_, &call_, &deadline_, &request_metadata_,
+              has_request_payload_ ? &request_payload_ : nullptr, cq_,
+              notify_cq, this)) {
+        TeardownRequest();
+        return;
+      }
     } else {
       if (!call_details_) {
         call_details_ = new grpc_call_details;
         grpc_call_details_init(call_details_);
       }
-      GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call(
-                                     server, &call_, call_details_,
-                                     &request_metadata_, cq_, notify_cq, this));
+      if (grpc_server_request_call(server, &call_, call_details_,
+                                   &request_metadata_, cq_, notify_cq,
+                                   this) != GRPC_CALL_OK) {
+        TeardownRequest();
+        return;
+      }
     }
   }
 
@@ -286,12 +292,10 @@ class Server::SyncRequestThreadManager : public ThreadManager {
     if (ok) {
       // Calldata takes ownership of the completion queue inside sync_req
       SyncRequest::CallData cd(server_, sync_req);
-      {
-        // Prepare for the next request
-        if (!IsShutdown()) {
-          sync_req->SetupRequest();  // Create new completion queue for sync_req
-          sync_req->Request(server_->c_server(), server_cq_->cq());
-        }
+      // Prepare for the next request
+      if (!IsShutdown()) {
+        sync_req->SetupRequest();  // Create new completion queue for sync_req
+        sync_req->Request(server_->c_server(), server_cq_->cq());
       }
 
       GPR_TIMER_SCOPE("cd.Run()", 0);
@@ -316,8 +320,8 @@ class Server::SyncRequestThreadManager : public ThreadManager {
   }
 
   void Shutdown() override {
-    server_cq_->Shutdown();
     ThreadManager::Shutdown();
+    server_cq_->Shutdown();
   }
 
   void Wait() override {
@@ -652,10 +656,11 @@ ServerInterface::RegisteredAsyncRequest::RegisteredAsyncRequest(
 void ServerInterface::RegisteredAsyncRequest::IssueRequest(
     void* registered_method, grpc_byte_buffer** payload,
     ServerCompletionQueue* notification_cq) {
-  grpc_server_request_registered_call(
-      server_->server(), registered_method, &call_, &context_->deadline_,
-      context_->client_metadata_.arr(), payload, call_cq_->cq(),
-      notification_cq->cq(), this);
+  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_registered_call(
+                                 server_->server(), registered_method, &call_,
+                                 &context_->deadline_,
+                                 context_->client_metadata_.arr(), payload,
+                                 call_cq_->cq(), notification_cq->cq(), this));
 }
 
 ServerInterface::GenericAsyncRequest::GenericAsyncRequest(
@@ -667,9 +672,10 @@ ServerInterface::GenericAsyncRequest::GenericAsyncRequest(
   grpc_call_details_init(&call_details_);
   GPR_ASSERT(notification_cq);
   GPR_ASSERT(call_cq);
-  grpc_server_request_call(server->server(), &call_, &call_details_,
-                           context->client_metadata_.arr(), call_cq->cq(),
-                           notification_cq->cq(), this);
+  GPR_ASSERT(GRPC_CALL_OK == grpc_server_request_call(
+                                 server->server(), &call_, &call_details_,
+                                 context->client_metadata_.arr(), call_cq->cq(),
+                                 notification_cq->cq(), this));
 }
 
 bool ServerInterface::GenericAsyncRequest::FinalizeResult(void** tag,
diff --git a/test/core/end2end/fuzzers/server_fuzzer.c b/test/core/end2end/fuzzers/server_fuzzer.c
index 3ddc1ae907..ef4c0a4bfd 100644
--- a/test/core/end2end/fuzzers/server_fuzzer.c
+++ b/test/core/end2end/fuzzers/server_fuzzer.c
@@ -72,8 +72,9 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   grpc_metadata_array_init(&request_metadata1);
   int requested_calls = 0;
 
-  grpc_server_request_call(server, &call1, &call_details1, &request_metadata1,
-                           cq, cq, tag(1));
+  GPR_ASSERT(GRPC_CALL_OK ==
+             grpc_server_request_call(server, &call1, &call_details1,
+                                      &request_metadata1, cq, cq, tag(1)));
   requested_calls++;
 
   grpc_event ev;
diff --git a/test/core/fling/server.c b/test/core/fling/server.c
index 0f0f22ffcf..b3a7fa21ec 100644
--- a/test/core/fling/server.c
+++ b/test/core/fling/server.c
@@ -77,8 +77,10 @@ typedef struct {
 
 static void request_call(void) {
   grpc_metadata_array_init(&request_metadata_recv);
-  grpc_server_request_call(server, &call, &call_details, &request_metadata_recv,
-                           cq, cq, tag(FLING_SERVER_NEW_REQUEST));
+  GPR_ASSERT(GRPC_CALL_OK ==
+             grpc_server_request_call(server, &call, &call_details,
+                                      &request_metadata_recv, cq, cq,
+                                      tag(FLING_SERVER_NEW_REQUEST)));
 }
 
 static void handle_unary_method(void) {
diff --git a/test/core/surface/completion_queue_test.c b/test/core/surface/completion_queue_test.c
index f9d88d6327..e6372a379c 100644
--- a/test/core/surface/completion_queue_test.c
+++ b/test/core/surface/completion_queue_test.c
@@ -144,7 +144,7 @@ static void test_cq_end_op(void) {
     cc = grpc_completion_queue_create(
         grpc_completion_queue_factory_lookup(&attr), &attr, NULL);
 
-    grpc_cq_begin_op(cc, tag);
+    GPR_ASSERT(grpc_cq_begin_op(cc, tag));
     grpc_cq_end_op(&exec_ctx, cc, tag, GRPC_ERROR_NONE,
                    do_nothing_end_completion, NULL, &completion);
 
@@ -233,7 +233,7 @@ static void test_pluck(void) {
         grpc_completion_queue_factory_lookup(&attr), &attr, NULL);
 
     for (i = 0; i < GPR_ARRAY_SIZE(tags); i++) {
-      grpc_cq_begin_op(cc, tags[i]);
+      GPR_ASSERT(grpc_cq_begin_op(cc, tags[i]));
       grpc_cq_end_op(&exec_ctx, cc, tags[i], GRPC_ERROR_NONE,
                      do_nothing_end_completion, NULL, &completions[i]);
     }
@@ -245,7 +245,7 @@ static void test_pluck(void) {
     }
 
     for (i = 0; i < GPR_ARRAY_SIZE(tags); i++) {
-      grpc_cq_begin_op(cc, tags[i]);
+      GPR_ASSERT(grpc_cq_begin_op(cc, tags[i]));
       grpc_cq_end_op(&exec_ctx, cc, tags[i], GRPC_ERROR_NONE,
                      do_nothing_end_completion, NULL, &completions[i]);
     }
diff --git a/test/core/surface/completion_queue_threading_test.c b/test/core/surface/completion_queue_threading_test.c
index 99d0fa4980..9996b6b840 100644
--- a/test/core/surface/completion_queue_threading_test.c
+++ b/test/core/surface/completion_queue_threading_test.c
@@ -107,7 +107,7 @@ static void test_too_many_plucks(void) {
   GPR_ASSERT(ev.type == GRPC_QUEUE_TIMEOUT);
 
   for (i = 0; i < GPR_ARRAY_SIZE(tags); i++) {
-    grpc_cq_begin_op(cc, tags[i]);
+    GPR_ASSERT(grpc_cq_begin_op(cc, tags[i]));
     grpc_cq_end_op(&exec_ctx, cc, tags[i], GRPC_ERROR_NONE,
                    do_nothing_end_completion, NULL, &completions[i]);
   }
@@ -153,7 +153,7 @@ static void producer_thread(void *arg) {
 
   gpr_log(GPR_INFO, "producer %d phase 1", opt->id);
   for (i = 0; i < TEST_THREAD_EVENTS; i++) {
-    grpc_cq_begin_op(opt->cc, (void *)(intptr_t)1);
+    GPR_ASSERT(grpc_cq_begin_op(opt->cc, (void *)(intptr_t)1));
   }
 
   gpr_log(GPR_INFO, "producer %d phase 1 done", opt->id);
diff --git a/test/cpp/microbenchmarks/bm_cq.cc b/test/cpp/microbenchmarks/bm_cq.cc
index 18308a2e16..a0c0414f2f 100644
--- a/test/cpp/microbenchmarks/bm_cq.cc
+++ b/test/cpp/microbenchmarks/bm_cq.cc
@@ -23,6 +23,7 @@
 #include <grpc++/completion_queue.h>
 #include <grpc++/impl/grpc_library.h>
 #include <grpc/grpc.h>
+#include <grpc/support/log.h>
 #include "test/cpp/microbenchmarks/helpers.h"
 
 extern "C" {
@@ -82,7 +83,7 @@ static void BM_Pass1Cpp(benchmark::State& state) {
     grpc_cq_completion completion;
     DummyTag dummy_tag;
     grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    grpc_cq_begin_op(c_cq, &dummy_tag);
+    GPR_ASSERT(grpc_cq_begin_op(c_cq, &dummy_tag));
     grpc_cq_end_op(&exec_ctx, c_cq, &dummy_tag, GRPC_ERROR_NONE,
                    DoneWithCompletionOnStack, NULL, &completion);
     grpc_exec_ctx_finish(&exec_ctx);
@@ -102,7 +103,7 @@ static void BM_Pass1Core(benchmark::State& state) {
   while (state.KeepRunning()) {
     grpc_cq_completion completion;
     grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    grpc_cq_begin_op(cq, NULL);
+    GPR_ASSERT(grpc_cq_begin_op(cq, NULL));
     grpc_cq_end_op(&exec_ctx, cq, NULL, GRPC_ERROR_NONE,
                    DoneWithCompletionOnStack, NULL, &completion);
     grpc_exec_ctx_finish(&exec_ctx);
@@ -121,7 +122,7 @@ static void BM_Pluck1Core(benchmark::State& state) {
   while (state.KeepRunning()) {
     grpc_cq_completion completion;
     grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    grpc_cq_begin_op(cq, NULL);
+    GPR_ASSERT(grpc_cq_begin_op(cq, NULL));
     grpc_cq_end_op(&exec_ctx, cq, NULL, GRPC_ERROR_NONE,
                    DoneWithCompletionOnStack, NULL, &completion);
     grpc_exec_ctx_finish(&exec_ctx);
diff --git a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
index f79db15a47..f109fe6251 100644
--- a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
+++ b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
@@ -78,7 +78,7 @@ static grpc_error* pollset_work(grpc_exec_ctx* exec_ctx, grpc_pollset* ps,
   }
 
   gpr_mu_unlock(&ps->mu);
-  grpc_cq_begin_op(g_cq, g_tag);
+  GPR_ASSERT(grpc_cq_begin_op(g_cq, g_tag));
   grpc_cq_end_op(exec_ctx, g_cq, g_tag, GRPC_ERROR_NONE, cq_done_cb, NULL,
                  (grpc_cq_completion*)gpr_malloc(sizeof(grpc_cq_completion)));
   grpc_exec_ctx_flush(exec_ctx);