Back out changeset b5ec7338bddf (bug 1236789) on a CLOSED TREE for causing assertions on most (but not all) debug test runs.

xpcom/threads/SharedThreadPool.h

@@ -55,11 +55,6 @@ public:
   // Forward behaviour to wrapped thread pool implementation.
   NS_FORWARD_SAFE_NSITHREADPOOL(mPool);
 
-  // Call this when dispatching from an event on the same
-  // threadpool that is about to complete. We should not create a new thread
-  // in that case since a thread is about to become idle.
-  nsresult TailDispatch(nsIRunnable *event) { return Dispatch(event, NS_DISPATCH_TAIL); }
-
   NS_IMETHOD DispatchFromScript(nsIRunnable *event, uint32_t flags) override {
       return Dispatch(event, flags);
   }

xpcom/threads/TaskQueue.cpp

@@ -193,7 +193,7 @@ TaskQueue::Runner::Run()
   // run in a loop here so that we don't hog the thread pool. This means we may
   // run on another thread next time, but we rely on the memory fences from
   // mQueueMonitor for thread safety of non-threadsafe tasks.
-  nsresult rv = mQueue->mPool->TailDispatch(this);
+  nsresult rv = mQueue->mPool->Dispatch(this, NS_DISPATCH_NORMAL);
   if (NS_FAILED(rv)) {
     // Failed to dispatch, shutdown!
     MonitorAutoLock mon(mQueue->mQueueMonitor);

xpcom/threads/nsIEventTarget.idl

@@ -40,18 +40,6 @@ interface nsIEventTarget : nsISupports
    */
   const unsigned long DISPATCH_SYNC = 1;
 
-  /**
-   * This flag specifies that the dispatch is occurring from a running event
-   * that was dispatched to the same event target, and that event is about to
-   * finish.
-   *
-   * A thread pool can use this as an optimization hint to not spin up
-   * another thread, since the current thread is about to become idle.
-   *
-   * These events are always async.
-   */
-  const unsigned long DISPATCH_TAIL = 2;
-
   /**
    * Check to see if this event target is associated with the current thread.
    *
@@ -103,5 +91,4 @@ interface nsIEventTarget : nsISupports
 // convenient aliases:
 #define NS_DISPATCH_NORMAL nsIEventTarget::DISPATCH_NORMAL
 #define NS_DISPATCH_SYNC   nsIEventTarget::DISPATCH_SYNC
-#define NS_DISPATCH_TAIL   nsIEventTarget::DISPATCH_TAIL
 %}

xpcom/threads/nsThreadPool.cpp

@@ -64,11 +64,11 @@ nsresult
 nsThreadPool::PutEvent(nsIRunnable* aEvent)
 {
   nsCOMPtr<nsIRunnable> event(aEvent);
-  return PutEvent(event.forget(), 0);
+  return PutEvent(event.forget());
 }
 
 nsresult
-nsThreadPool::PutEvent(already_AddRefed<nsIRunnable>&& aEvent, uint32_t aFlags)
+nsThreadPool::PutEvent(already_AddRefed<nsIRunnable>&& aEvent)
 {
   // Avoid spawning a new thread while holding the event queue lock...
 
@@ -86,7 +86,6 @@ nsThreadPool::PutEvent(already_AddRefed<nsIRunnable>&& aEvent, uint32_t aFlags)
 
     // Make sure we have a thread to service this event.
     if (mThreads.Count() < (int32_t)mThreadLimit &&
-        !(aFlags & NS_DISPATCH_TAIL) &&
         // Spawn a new thread if we don't have enough idle threads to serve
         // pending events immediately.
         mEvents.Count(lock) >= mIdleCount) {
@@ -273,7 +272,7 @@ nsThreadPool::Dispatch(already_AddRefed<nsIRunnable>&& aEvent, uint32_t aFlags)
     }
   } else {
     NS_ASSERTION(aFlags == NS_DISPATCH_NORMAL, "unexpected dispatch flags");
-    PutEvent(Move(aEvent), aFlags);
+    PutEvent(Move(aEvent));
   }
   return NS_OK;
 }

xpcom/threads/nsThreadPool.h

@@ -37,7 +37,7 @@ private:
 
   void ShutdownThread(nsIThread* aThread);
   nsresult PutEvent(nsIRunnable* aEvent);
-  nsresult PutEvent(already_AddRefed<nsIRunnable>&& aEvent, uint32_t aFlags);
+  nsresult PutEvent(already_AddRefed<nsIRunnable>&& aEvent);
 
   nsCOMArray<nsIThread> mThreads;
   mozilla::Mutex        mMutex;