MessagePumpDefault can spin for up to 1 ms on Windows

base/message_loop/message_pump_default.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/message_loop/message_pump_default.h"
 
+#include <algorithm>
+
 #include "base/logging.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 
 #if defined(OS_MACOSX)
 #include "base/mac/scoped_nsautorelease_pool.h"
 #endif
 
 namespace base {
 
@@ skipping 30 matching lines @@
 
     if (did_work)
       continue;
 
     ThreadRestrictions::ScopedAllowWait allow_wait;
     if (delayed_work_time_.is_null()) {
       event_.Wait();
     } else {
       TimeDelta delay = delayed_work_time_ - TimeTicks::Now();
       if (delay > TimeDelta()) {
+#if defined(OS_WIN)
+        // crbug.com/487724: on Windows, waiting for less than 1 ms results in
+        // returning from TimedWait promptly and spinning the loop.
+        TimeDelta min_delay = TimeDelta::FromMilliseconds(1);

[brucedawson, 2016/06/21 21:35:11]

This should be const to make the intent clearer.

[stanisc, 2016/06/22 01:28:07]

Done.

+        do {
+          delay = std::max(delay, min_delay);
+          if (event_.TimedWait(delay))
+            break;
+
+          // TimedWait can time out earlier than the specified |delay| on
+          // Windows. It doesn't make sense to run the outer loop in that case
+          // because there isn't going to be any new work. It is less overhead
+          // go just go back to wait.
+          // In practice this inner wait loop might have up to 3 iterations.
+          delay = delayed_work_time_ - TimeTicks::Now();
+        } while (delay > TimeDelta());
+#else
         event_.TimedWait(delay);
+#endif
       } else {
         // It looks like delayed_work_time_ indicates a time in the past, so we
         // need to call DoDelayedWork now.
         delayed_work_time_ = TimeTicks();
       }
     }
     // Since event_ is auto-reset, we don't need to do anything special here
     // other than service each delegate method.
   }
 
@@ skipping 12 matching lines @@
 
 void MessagePumpDefault::ScheduleDelayedWork(
     const TimeTicks& delayed_work_time) {
   // We know that we can't be blocked on Wait right now since this method can
   // only be called on the same thread as Run, so we only need to update our
   // record of how long to sleep when we do sleep.
   delayed_work_time_ = delayed_work_time;
 }
 
 }  // namespace base