Increase tick precision in TaskQueue on Windows 64.

webrtc/base/task_queue_win.cc

Index: webrtc/base/task_queue_win.cc
diff --git a/webrtc/base/task_queue_win.cc b/webrtc/base/task_queue_win.cc
index 5850b2947ed2822f1d646efbff6a00af91343854..17bb3277596f1939fdeacf1536972d96f62116e4 100644
--- a/webrtc/base/task_queue_win.cc
+++ b/webrtc/base/task_queue_win.cc
@@ -66,6 +66,16 @@ ThreadPriority TaskQueuePriorityToThreadPriority(Priority priority) {
   }
   return kNormalPriority;
 }
+
+DWORD GetTick() {
+  static const UINT kPeriod = 1;
+  bool high_res = (timeBeginPeriod(kPeriod) == TIMERR_NOERROR);
+  DWORD ret = timeGetTime();

[henrika_webrtc, 2017/03/03 12:24:55]

What happens if high_res is false?

[tommi, 2017/03/03 12:39:01]

Default behavior of timeGetTime(): 
https://msdn.microsoft.com/en-us/library/windows/desktop/dd757629(v=vs.85).aspx

In practice this only affects tests at the moment btw, since in Chrome we use
Chrome's task scheduler on Windows.

[henrika_webrtc, 2017/03/03 12:42:32]

Got it. I was more thinking about what will be returned if high_res is false.

[tommi, 2017/03/03 12:59:34]

TIMERR_NOCANDO is one possibility. I don't think that's likely, but I don't want
to have a mismatched call to timeEndPeriod if it does, since these calls affect
all processes.

[henrika_webrtc, 2017/03/03 13:00:53]

Sorry. My brain added a {} below and I therefore figured that you did not do
return in case of false.

My bad. Ignore.

[tommi, 2017/03/03 13:10:21]

ack :)

+  if (high_res)
+    timeEndPeriod(kPeriod);
+  return ret;
+}
+
 }  // namespace
 
 class TaskQueue::MultimediaTimer {
@@ -214,7 +224,7 @@ void TaskQueue::PostDelayedTask(std::unique_ptr<QueuedTask> task,
   // GetTickCount() returns a fairly coarse tick count (resolution or about 8ms)
   // so this compensation isn't that accurate, but since we have unused 32 bits
   // on Win64, we might as well use them.
-  wparam = (static_cast<WPARAM>(::GetTickCount()) << 32) | milliseconds;
+  wparam = (static_cast<WPARAM>(GetTick()) << 32) | milliseconds;
 #else
   wparam = milliseconds;
 #endif
@@ -325,7 +335,7 @@ bool TaskQueue::ProcessQueuedMessages(DelayedTasks* delayed_tasks,
           uint32_t milliseconds = msg.wParam & 0xFFFFFFFF;
 #if defined(_WIN64)
           // Subtract the time it took to queue the timer.
-          const DWORD now = GetTickCount();
+          const DWORD now = GetTick();
           DWORD post_time = now - (msg.wParam >> 32);
           milliseconds =
               post_time > milliseconds ? 0 : milliseconds - post_time;