MessagePumpDefault can spin for up to 1 ms on Windows

base/message_loop/message_pump_default.cc

Index: base/message_loop/message_pump_default.cc
diff --git a/base/message_loop/message_pump_default.cc b/base/message_loop/message_pump_default.cc
index 0fac8b3c9c9adbe7597b59096a30ba2a9ad7e935..e6594747cf258d6fedc22eee00a5f6a28b507b01 100644
--- a/base/message_loop/message_pump_default.cc
+++ b/base/message_loop/message_pump_default.cc
@@ -4,6 +4,8 @@
 
 #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"
@@ -54,7 +56,25 @@ void MessagePumpDefault::Run(Delegate* delegate) {
     } 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.