Bug 1764119 - Part 2: Don't check gXPCOMThreadsShutdown in ThreadEventTarget::Dispatch, r=xpcom-reviewers,kmag,jstutte

We already have a mechanism for ending threads accepting new messages
when they are shut down, so this only allows tasks started from thread
shutdown tasks during xpcom shutdown to behave consistently.

We already didn't prevent dispatching to the background thread pool at
this time, so it should make little difference there as well, and may
just instead save us from deadlocks where code expects a dispatch to
succeed and it does not during actor shutdown.

This patch both relaxes the check to only be a NS_ASSERTION, and relaxes
it to allow dispatching to the current thread even after
xpcom-shutdown-threads as that thread is definitely still alive.

Differential Revision: https://phabricator.services.mozilla.com/D144592

xpcom/threads/ThreadEventTarget.cpp

@@ -23,7 +23,12 @@ using namespace mozilla;
 
 ThreadEventTarget::ThreadEventTarget(ThreadTargetSink* aSink,
                                      bool aIsMainThread)
-    : mSink(aSink), mIsMainThread(aIsMainThread) {
+    : mSink(aSink)
+#ifdef DEBUG
+      ,
+      mIsMainThread(aIsMainThread)
+#endif
+{
   mThread = PR_GetCurrentThread();
 }
 
@@ -52,10 +57,9 @@ ThreadEventTarget::Dispatch(already_AddRefed<nsIRunnable> aEvent,
     return NS_ERROR_INVALID_ARG;
   }
 
-  if (gXPCOMThreadsShutDown && !mIsMainThread) {
-    NS_ASSERTION(false, "Failed Dispatch after xpcom-shutdown-threads");
-    return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
-  }
+  NS_ASSERTION(!gXPCOMThreadsShutDown || mIsMainThread ||
+                   PR_GetCurrentThread() == mThread,
+               "Dispatch to non-main thread after xpcom-shutdown-threads");
 
   LogRunnable::LogDispatch(event.get());
 

xpcom/threads/ThreadEventTarget.h

@@ -47,7 +47,9 @@ class ThreadEventTarget final : public nsISerialEventTarget {
   ~ThreadEventTarget();
 
   RefPtr<ThreadTargetSink> mSink;
+#ifdef DEBUG
   bool mIsMainThread;
+#endif
 };
 
 }  // namespace mozilla