change mutex to spinlock

src/core/lib/surface/completion_queue.c

@@ -45,6 +45,7 @@
 #include "src/core/lib/iomgr/pollset.h"
 #include "src/core/lib/iomgr/timer.h"
 #include "src/core/lib/profiling/timers.h"
+#include "src/core/lib/support/spinlock.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/surface/api_trace.h"
 #include "src/core/lib/surface/call.h"
@@ -68,8 +69,8 @@ typedef struct {
  * Currently this is only used in completion queues whose completion_type is
  * GRPC_CQ_NEXT */
 typedef struct grpc_cq_event_queue {
-  /* Mutex to serialize consumers i.e pop() operations */
-  gpr_mu queue_mu;
+  /* spinlock to serialize consumers i.e pop() operations */
+  gpr_spinlock queue_lock;
 
   gpr_mpscq queue;
 
@@ -142,13 +143,12 @@ static void on_pollset_shutdown_done(grpc_exec_ctx *exec_ctx, void *cc,
 
 static void cq_event_queue_init(grpc_cq_event_queue *q) {
   gpr_mpscq_init(&q->queue);
-  gpr_mu_init(&q->queue_mu);
+  q->queue_lock = GPR_SPINLOCK_INITIALIZER;
   gpr_atm_no_barrier_store(&q->num_queue_items, 0);
 }
 
 static void cq_event_queue_destroy(grpc_cq_event_queue *q) {
   gpr_mpscq_destroy(&q->queue);
-  gpr_mu_destroy(&q->queue_mu);
 }
 
 static void cq_event_queue_push(grpc_cq_event_queue *q, grpc_cq_completion *c) {
@@ -157,9 +157,12 @@ static void cq_event_queue_push(grpc_cq_event_queue *q, grpc_cq_completion *c) {
 }
 
 static grpc_cq_completion *cq_event_queue_pop(grpc_cq_event_queue *q) {
-  gpr_mu_lock(&q->queue_mu);
-  grpc_cq_completion *c = (grpc_cq_completion *)gpr_mpscq_pop(&q->queue);
-  gpr_mu_unlock(&q->queue_mu);
+  grpc_cq_completion *c = NULL;
+  if (gpr_spinlock_trylock(&q->queue_lock)) {
+    c = (grpc_cq_completion *)gpr_mpscq_pop(&q->queue);
+    gpr_spinlock_unlock(&q->queue_lock);
+  }
+
   if (c) {
     gpr_atm_no_barrier_fetch_add(&q->num_queue_items, -1);
   }