1 files changed, 10 insertions, 8 deletions
diff --git a/absl/synchronization/mutex.cc b/absl/synchronization/mutex.cc
index 3af4cda9..376ea794 100644
--- a/absl/synchronization/mutex.cc
+++ b/absl/synchronization/mutex.cc
@@ -109,7 +109,7 @@ static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu,
                                           bool locking, bool trylock,
                                           bool read_lock);
 
-void RegisterMutexProfiler(void (*fn)(int64_t wait_timestamp)) {
+void RegisterMutexProfiler(void (*fn)(int64_t wait_cycles)) {
   submit_profile_data.Store(fn);
 }
 
@@ -2315,16 +2315,18 @@ ABSL_ATTRIBUTE_NOINLINE void Mutex::UnlockSlow(SynchWaitParams *waitp) {
   }                            // end of for(;;)-loop
 
   if (wake_list != kPerThreadSynchNull) {
-    int64_t enqueue_timestamp = wake_list->waitp->contention_start_cycles;
-    bool cond_waiter = wake_list->cond_waiter;
+    int64_t wait_cycles = 0;
+    int64_t now = base_internal::CycleClock::Now();
     do {
+      // Sample lock contention events only if the waiter was trying to acquire
+      // the lock, not waiting on a condition variable or Condition.
+      if (!wake_list->cond_waiter) {
+        wait_cycles += (now - wake_list->waitp->contention_start_cycles);
+        wake_list->waitp->contention_start_cycles = now;
+      }
       wake_list = Wakeup(wake_list);              // wake waiters
     } while (wake_list != kPerThreadSynchNull);
-    if (!cond_waiter) {
-      // Sample lock contention events only if the (first) waiter was trying to
-      // acquire the lock, not waiting on a condition variable or Condition.
-      int64_t wait_cycles =
-          base_internal::CycleClock::Now() - enqueue_timestamp;
+    if (wait_cycles > 0) {
       mutex_tracer("slow release", this, wait_cycles);
       ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0);
       submit_profile_data(wait_cycles);