From fa7339357409a133b25a01bcb13ba093d088e9ce Mon Sep 17 00:00:00 2001
From: Danil Chapovalov <danilchap@webrtc.org>
Date: Mon, 13 Jan 2020 12:56:13 +0100
Subject: [PATCH] In TaskQueueWin fix race in canceling MutlimediaTimer

Bug: webrtc:11232
Change-Id: I371f0b78a572c94f2eefd8e0859eed88bce9e37e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/165762
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30232}
---
 rtc_base/task_queue_win.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/rtc_base/task_queue_win.cc b/rtc_base/task_queue_win.cc
index dd825d2fdc..8c11b8764a 100644
--- a/rtc_base/task_queue_win.cc
+++ b/rtc_base/task_queue_win.cc
@@ -134,11 +134,15 @@ class MultimediaTimer {
   }
 
   void Cancel() {
-    ::ResetEvent(event_);
     if (timer_id_) {
       ::timeKillEvent(timer_id_);
       timer_id_ = 0;
     }
+    // Now that timer is killed and not able to set the event, reset the event.
+    // Doing it in opposite order is racy because event may be set between
+    // event was reset and timer is killed leaving MultimediaTimer in surprising
+    // state where both event is set and timer is canceled.
+    ::ResetEvent(event_);
   }
 
   HANDLE* event_for_wait() { return &event_; }