Fixed a problem with spurious wakeups.

runtime/vm/thread_macos.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <sys/errno.h>
 
 #include "vm/thread.h"
 
 #include "vm/assert.h"
 
@@ skipping 175 matching lines @@
   int result = pthread_mutex_unlock(data_.mutex());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 
 Monitor::WaitResult Monitor::Wait(int64_t millis) {
   // TODO(iposva): Do we need to track lock owners?
   Monitor::WaitResult retval = kNotified;
   if (millis == 0) {
     // Wait forever.
+    // If the thread receives a signal, pthread_cond_wait may return 0,
+    // because of a spurious wakeup.
     int result = pthread_cond_wait(data_.cond(), data_.mutex());
     VALIDATE_PTHREAD_RESULT(result);
   } else {
     struct timespec ts;
     int64_t secs = millis / 1000;
     int64_t nanos = (millis - (secs * 1000)) * 1000000;
     ts.tv_sec = secs;
     ts.tv_nsec = nanos;
     int result = pthread_cond_timedwait_relative_np(data_.cond(),
                                                     data_.mutex(),
@@ skipping 14 matching lines @@
 }
 
 
 void Monitor::NotifyAll() {
   // TODO(iposva): Do we need to track lock owners?
   int result = pthread_cond_broadcast(data_.cond());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 }  // namespace dart