From 325021f37a8cfd8135e1ca485ea401569f041c74 Mon Sep 17 00:00:00 2001
From: Iulian Moraru <imoraru@mozilla.com>
Date: Sat, 25 Feb 2023 14:30:52 +0200
Subject: [PATCH] Backed out changeset 9f0d0ce9c0df (bug 1770658) for causing
 dt failures on browser_aboutdebugging_devtoolstoolbox_reload.js. CLOSED TREE

---
 xpcom/threads/TimerThread.cpp | 49 ++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 26 deletions(-)

diff --git a/xpcom/threads/TimerThread.cpp b/xpcom/threads/TimerThread.cpp
index 3306a0a3bcca..b7dcba65bd75 100644
--- a/xpcom/threads/TimerThread.cpp
+++ b/xpcom/threads/TimerThread.cpp
@@ -800,34 +800,31 @@ nsresult TimerThread::AddTimer(nsTimerImpl* aTimer,
     return rv;
   }
 
-  // Fire this timer immediately (and skip adding it to our timer list) if the
-  // delay is 0, which are meant to be run as soon as possible. This has less
-  // overhead than waking up the timer thread and handling it there while still
-  // maintaining timer ordering and response time.
-  const bool fireImmediately = aTimer->mDelay.IsZero();
-  if (fireImmediately) {
-    RefPtr<nsTimerImpl> timerRef(aTimer);
-    LogTimerEvent::Run run(aTimer);
-    PostTimerEvent(timerRef.forget());
-  } else {
-    // Awaken the timer thread if this timer wants to fire *before* the Timer
-    // Thread is scheduled to wake up. We don't track this directly but we know
-    // that we will have attempted to wake up at the timeout for the first time
-    // in our list (if it exists), so we can use that. Note: This is true even
-    // if the timer has since been canceled.
-    const bool wakeUpTimerThread =
-        mWaiting &&
-        (mTimers.Length() == 0 || aTimer->mTimeout < mTimers[0].Timeout());
+  // Awaken the timer thread if:
+  // - This timer wants to fire *before* the Timer Thread is scheduled to wake
+  //   up. We don't track this directly but we know that we will have attempted
+  //   to wake up at the timeout for the first time in our list (if it exists),
+  //   so we can use that. Note: This is true even if the timer has since been
+  //   canceled.
+  // AND/OR
+  // - The delay is 0, which is usually meant to be run as soon as possible.
+  //   Note: Even if the thread is scheduled to wake up now/soon, on some
+  //   systems there could be a significant delay compared to notifying, which
+  //   is almost immediate; and some users of 0-delay depend on it being this
+  //   fast!
+  const bool wakeUpTimerThread =
+      mWaiting &&
+      (mTimers.Length() == 0 || aTimer->mTimeout < mTimers[0].Timeout() ||
+       aTimer->mDelay.IsZero());
 
-    // Add the timer to our list.
-    if (!AddTimerInternal(aTimer)) {
-      return NS_ERROR_OUT_OF_MEMORY;
-    }
+  // Add the timer to our list.
+  if (!AddTimerInternal(aTimer)) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
 
-    if (wakeUpTimerThread) {
-      mNotified = true;
-      mMonitor.Notify();
-    }
+  if (wakeUpTimerThread) {
+    mNotified = true;
+    mMonitor.Notify();
   }
 
   if (profiler_thread_is_being_profiled_for_markers(mProfilerThreadId)) {