From 74d28327be3a4cc1d2109a7ed16f669a79fad1d5 Mon Sep 17 00:00:00 2001
From: Gerald Squelart <gsquelart@mozilla.com>
Date: Thu, 19 May 2022 20:31:25 +0000
Subject: [PATCH] Bug 1767396 - Don't wake up the timer thread when removing
 timers - r=florian,smaug

Differential Revision: https://phabricator.services.mozilla.com/D146031
---
 xpcom/threads/TimerThread.cpp | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/xpcom/threads/TimerThread.cpp b/xpcom/threads/TimerThread.cpp
index acb8aeffde07..ea3daeb83395 100644
--- a/xpcom/threads/TimerThread.cpp
+++ b/xpcom/threads/TimerThread.cpp
@@ -686,11 +686,14 @@ nsresult TimerThread::RemoveTimer(nsTimerImpl* aTimer,
     return NS_ERROR_NOT_AVAILABLE;
   }
 
-  // Awaken the timer thread.
-  if (mWaiting) {
-    mNotified = true;
-    mMonitor.Notify();
-  }
+  // Note: The timer thread is *not* awoken.
+  // The removed-timer entry is just left null, and will be reused (by a new or
+  // re-set timer) or discarded (when the timer thread logic handles non-null
+  // timers around it).
+  // If this was the front timer, and in the unlikely case that its entry is not
+  // soon reused by a re-set timer, the timer thread will wake up at the
+  // previously-scheduled time, but will quickly notice that there is no actual
+  // pending timer, and will restart its wait until the following real timeout.
 
   if (profiler_thread_is_being_profiled_for_markers(mProfilerThreadId)) {
     nsAutoCString name;