Have server hold a reference to completion queues

In the presence of garbage collectors, this helps ensure that completion
queues outlive the servers that depend upon them.

src/core/surface/completion_queue.c

@@ -132,9 +132,22 @@ static event *add_locked(grpc_completion_queue *cc, grpc_completion_type type,
   return ev;
 }
 
+void grpc_cq_internal_ref(grpc_completion_queue *cc) {
+  gpr_ref(&cc->refs);
+}
+
+void grpc_cq_internal_unref(grpc_completion_queue *cc) {
+  if (gpr_unref(&cc->refs)) {
+    GPR_ASSERT(!cc->shutdown);
+    GPR_ASSERT(cc->shutdown_called);
+    cc->shutdown = 1;
+    gpr_cv_broadcast(GRPC_POLLSET_CV(&cc->pollset));
+  }
+}
+
 void grpc_cq_begin_op(grpc_completion_queue *cc, grpc_call *call,
                       grpc_completion_type type) {
-  gpr_ref(&cc->refs);
+  grpc_cq_internal_ref(cc);
   if (call) grpc_call_internal_ref(call);
 #ifndef NDEBUG
   gpr_atm_no_barrier_fetch_add(&cc->pending_op_count[type], 1);
@@ -148,12 +161,7 @@ static void end_op_locked(grpc_completion_queue *cc,
 #ifndef NDEBUG
   GPR_ASSERT(gpr_atm_full_fetch_add(&cc->pending_op_count[type], -1) > 0);
 #endif
-  if (gpr_unref(&cc->refs)) {
+  grpc_cq_internal_unref(cc);
-    GPR_ASSERT(!cc->shutdown);
-    GPR_ASSERT(cc->shutdown_called);
-    cc->shutdown = 1;
-    gpr_cv_broadcast(GRPC_POLLSET_CV(&cc->pollset));
-  }
 }
 
 void grpc_cq_end_server_shutdown(grpc_completion_queue *cc, void *tag) {

src/core/surface/completion_queue.h

@@ -43,6 +43,9 @@
    grpc_event_finish */
 typedef void (*grpc_event_finish_func)(void *user_data, grpc_op_error error);
 
+void grpc_cq_internal_ref(grpc_completion_queue *cc);
+void grpc_cq_internal_unref(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 */
 void grpc_cq_begin_op(grpc_completion_queue *cc, grpc_call *call,

src/core/surface/server.c

@@ -262,6 +262,7 @@ static void server_ref(grpc_server *server) {
 
 static void server_unref(grpc_server *server) {
   registered_method *rm;
+  size_t i;
   if (gpr_unref(&server->internal_refcount)) {
     grpc_channel_args_destroy(server->channel_args);
     gpr_mu_destroy(&server->mu);
@@ -275,6 +276,9 @@ static void server_unref(grpc_server *server) {
       requested_call_array_destroy(&rm->requested);
       gpr_free(rm);
     }
+    for (i = 0; i < server->cq_count; i++) {
+      grpc_cq_internal_unref(server->cqs[i]);
+    }
     gpr_free(server->cqs);
     gpr_free(server->pollsets);
     gpr_free(server->shutdown_tags);
@@ -601,6 +605,7 @@ static void addcq(grpc_server *server, grpc_completion_queue *cq) {
   for (i = 0; i < server->cq_count; i++) {
     if (server->cqs[i] == cq) return;
   }
+  grpc_cq_internal_ref(cq);
   n = server->cq_count++;
   server->cqs = gpr_realloc(server->cqs,
                             server->cq_count * sizeof(grpc_completion_queue *));