Backed out 3 changesets (bug 1768581, bug 1709184) for causing mochitest failures on LateWriteChecks.cpp. CLOSED TREE

Backed out changeset c49173f72e0d (bug 1768581)
Backed out changeset a4c2b2d0b63a (bug 1709184)
Backed out changeset 1181bdcde598 (bug 1709184)

xpcom/base/AppShutdown.cpp

@@ -315,7 +315,6 @@ bool AppShutdown::IsRestarting() {
 
 #ifdef DEBUG
 static bool sNotifyingShutdownObservers = false;
-static bool sAdvancingShutdownPhase = false;
 
 bool AppShutdown::IsNoOrLegalShutdownTopic(const char* aTopic) {
   if (!XRE_IsParentProcess()) {
@@ -333,12 +332,6 @@ void AppShutdown::AdvanceShutdownPhaseInternal(
     ShutdownPhase aPhase, bool doNotify, const char16_t* aNotificationData,
     const nsCOMPtr<nsISupports>& aNotificationSubject) {
   AssertIsOnMainThread();
-#ifdef DEBUG
-  // Prevent us from re-entrance
-  MOZ_ASSERT(!sAdvancingShutdownPhase);
-  sAdvancingShutdownPhase = true;
-  auto exit = MakeScopeExit([] { sAdvancingShutdownPhase = false; });
-#endif
 
   // We ensure that we can move only forward. We cannot
   // MOZ_ASSERT here as there are some tests that fire
@@ -347,43 +340,24 @@ void AppShutdown::AdvanceShutdownPhaseInternal(
   if (sCurrentShutdownPhase >= aPhase) {
     return;
   }
-
-  nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
-  if (sCurrentShutdownPhase >= ShutdownPhase::AppShutdownConfirmed) {
-    // Give runnables dispatched between two calls to AdvanceShutdownPhase
-    // a chance to run before actually advancing the phase. We must do this
-    // only after we passed the point of no return and thus can expect a linear
-    // flow through our shutdown phases. This way the processing is also
-    // covered by the terminator's timer of the previous phase.
-    // Note that this affects only main thread runnables, such that the correct
-    // way of ensuring shutdown processing remains to have an async shutdown
-    // blocker.
-    if (thread) {
-      NS_ProcessPendingEvents(thread);
-    }
-  }
-
-  // From now on any IsInOrBeyond checks will find the new phase set.
   sCurrentShutdownPhase = aPhase;
 
+  // TODO: Bug 1768581
+  // We think it would be more logical to have the following order here:
+  //    AppShutdown::MaybeFastShutdown(aPhase);
+  //    sTerminator->AdvancePhase(aPhase);
+  //    obsService->NotifyObservers(...);
+  //    mozilla::KillClearOnShutdown(aPhase);
+
 #ifndef ANDROID
   if (sTerminator) {
     sTerminator->AdvancePhase(aPhase);
   }
 #endif
 
-  AppShutdown::MaybeFastShutdown(aPhase);
-
-  // This will null out the gathered pointers for this phase synchronously.
-  // Note that we keep the old order here to avoid breakage, so be aware that
-  // the notifications fired below will find these already cleared in case
-  // you expected the opposite.
   mozilla::KillClearOnShutdown(aPhase);
 
-  // Empty our MT event queue to process any side effects thereof.
-  if (thread) {
-    NS_ProcessPendingEvents(thread);
-  }
+  AppShutdown::MaybeFastShutdown(aPhase);
 
   if (doNotify) {
     const char* aTopic = AppShutdown::GetObserverKey(aPhase);
@@ -397,10 +371,6 @@ void AppShutdown::AdvanceShutdownPhaseInternal(
 #endif
         obsService->NotifyObservers(aNotificationSubject, aTopic,
                                     aNotificationData);
-        // Empty our MT event queue again after the notification has finished
-        if (thread) {
-          NS_ProcessPendingEvents(thread);
-        }
       }
     }
   }

xpcom/build/XPCOMInit.cpp

@@ -585,6 +585,7 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
 
     // This must happen after the shutdown of media and widgets, which
     // are triggered by the NS_XPCOM_SHUTDOWN_OBSERVER_ID notification.
+    NS_ProcessPendingEvents(thread);
     gfxPlatform::ShutdownLayersIPC();
 
     mozilla::AppShutdown::AdvanceShutdownPhase(
@@ -594,11 +595,11 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
     // dispatches to non main-thread threads.
     ThreadEventTarget::XPCOMShutdownThreadsNotificationFinished();
 #endif
+    NS_ProcessPendingEvents(thread);
 
     // Shutdown the timer thread and all timers that might still be alive
     nsTimerImpl::Shutdown();
 
-    // Have an extra round of processing after the timers went away.
     NS_ProcessPendingEvents(thread);
 
     // Shutdown all remaining threads.  This method does not return until
@@ -616,9 +617,11 @@ nsresult ShutdownXPCOM(nsIServiceManager* aServMgr) {
     // XPCOMShutdownFinal is the default phase for ClearOnShutdown.
     // This AdvanceShutdownPhase will thus free most ClearOnShutdown()'ed
     // smart pointers. Some destructors may fire extra main thread runnables
-    // that will be processed inside AdvanceShutdownPhase.
+    // that will be processed below.
     AppShutdown::AdvanceShutdownPhase(ShutdownPhase::XPCOMShutdownFinal);
 
+    NS_ProcessPendingEvents(thread);
+
     // Shutdown the main thread, processing our last round of events, and then
     // mark that we've finished main thread event processing.
     nsThreadManager::get().ShutdownMainThread();