From 06dd7edc6c6d56394be9feba131edfae176268ab Mon Sep 17 00:00:00 2001
From: Brad Werth <bwerth@mozilla.com>
Date: Tue, 8 Nov 2022 15:53:35 +0000
Subject: [PATCH] Bug 1798651 Part 2: Make WinWindowOcclusionTracker::ShutDown
 timeout after 2 seconds. r=gfx-reviewers,sotaro

Differential Revision: https://phabricator.services.mozilla.com/D161195
---
 widget/windows/WinWindowOcclusionTracker.cpp | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/widget/windows/WinWindowOcclusionTracker.cpp b/widget/windows/WinWindowOcclusionTracker.cpp
index 1b20b700c082..9aa339ea2c6a 100644
--- a/widget/windows/WinWindowOcclusionTracker.cpp
+++ b/widget/windows/WinWindowOcclusionTracker.cpp
@@ -371,15 +371,22 @@ void WinWindowOcclusionTracker::ShutDown() {
 
   sTracker->Destroy();
 
+  // Our shutdown task could hang. Since we're shutting down,
+  // that's not a critical problem. We set a reasonable amount
+  // of time to wait for shutdown, and if it succeeds within
+  // that time, we correctly stop our tracker thread. If it
+  // times out, we just leak the memory and proceed.
+  static const PRIntervalTime TIMEOUT = PR_TicksPerSecond() * 2;
   layers::SynchronousTask task("WinWindowOcclusionTracker");
   RefPtr<Runnable> runnable =
       WrapRunnable(RefPtr<WindowOcclusionCalculator>(
                        WindowOcclusionCalculator::GetInstance()),
                    &WindowOcclusionCalculator::Shutdown, &task);
   OcclusionCalculatorLoop()->PostTask(runnable.forget());
-  task.Wait();
-
-  sTracker->mThread->Stop();
+  nsresult rv = task.Wait(TIMEOUT);
+  if (rv == NS_OK) {
+    sTracker->mThread->Stop();
+  }
 
   WindowOcclusionCalculator::ClearInstance();
   sTracker = nullptr;