Bug 968016 - Add methods to SharedThreadPools and MediaTaskQueues to report whether we're running on one of their threads. r=kinetik

content/media/MediaTaskQueue.cpp

@@ -90,6 +90,17 @@ MediaTaskQueue::IsEmpty()
   return mTasks.empty();
 }
 
+bool
+MediaTaskQueue::IsCurrentThreadIn()
+{
+#ifdef DEBUG
+  MonitorAutoLock mon(mQueueMonitor);
+  return NS_GetCurrentThread() == mRunningThread;
+#else
+  return false;
+#endif
+}
+
 nsresult
 MediaTaskQueue::Runner::Run()
 {
@@ -97,6 +108,7 @@ MediaTaskQueue::Runner::Run()
   {
     MonitorAutoLock mon(mQueue->mQueueMonitor);
     MOZ_ASSERT(mQueue->mIsRunning);
+    mQueue->mRunningThread = NS_GetCurrentThread();
     if (mQueue->mTasks.size() == 0) {
       mQueue->mIsRunning = false;
       mon.NotifyAll();
@@ -120,6 +132,7 @@ MediaTaskQueue::Runner::Run()
       // No more events to run. Exit the task runner.
       mQueue->mIsRunning = false;
       mon.NotifyAll();
+      mQueue->mRunningThread = nullptr;
       return NS_OK;
     }
   }
@@ -129,13 +142,20 @@ MediaTaskQueue::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->Dispatch(this, NS_DISPATCH_NORMAL);
-  if (NS_FAILED(rv)) {
-    // Failed to dispatch, shutdown!
+  {
     MonitorAutoLock mon(mQueue->mQueueMonitor);
-    mQueue->mIsRunning = false;
-    mQueue->mIsShutdown = true;
-    mon.NotifyAll();
+    // Note: Hold the monitor *before* we dispatch, in case we context switch
+    // to another thread pool in the queue immediately and take the lock in the
+    // other thread; mRunningThread could be set to the new thread's value and
+    // then incorrectly anulled below in that case.
+    nsresult rv = mQueue->mPool->Dispatch(this, NS_DISPATCH_NORMAL);
+    if (NS_FAILED(rv)) {
+      // Failed to dispatch, shutdown!
+      mQueue->mIsRunning = false;
+      mQueue->mIsShutdown = true;
+      mon.NotifyAll();
+    }
+    mQueue->mRunningThread = nullptr;
   }
 
   return NS_OK;

content/media/MediaTaskQueue.h

@@ -43,6 +43,10 @@ public:
 
   bool IsEmpty();
 
+  // Returns true if the current thread is currently running a Runnable in
+  // the task queue. This is for debugging/validation purposes only.
+  bool IsCurrentThreadIn();
+
 private:
 
   // Blocks until all task finish executing. Called internally by methods
@@ -58,6 +62,11 @@ private:
   // Queue of tasks to run.
   std::queue<RefPtr<nsIRunnable>> mTasks;
 
+  // The thread currently running the task queue. We store a reference
+  // to this so that IsCurrentThreadIn() can tell if the current thread
+  // is the thread currently running in the task queue.
+  RefPtr<nsIThread> mRunningThread;
+
   // True if we've dispatched an event to the pool to execute events from
   // the queue.
   bool mIsRunning;

content/media/SharedThreadPool.cpp

@@ -155,7 +155,7 @@ NS_IMETHODIMP_(nsrefcnt) SharedThreadPool::Release(void)
   return 0;
 }
 
-NS_IMPL_QUERY_INTERFACE1(SharedThreadPool, nsIThreadPool)
+NS_IMPL_QUERY_INTERFACE2(SharedThreadPool, nsIThreadPool, nsIEventTarget)
 
 SharedThreadPool::SharedThreadPool(const nsCString& aName,
                                    nsIThreadPool* aPool)

content/media/SharedThreadPool.h

@@ -44,7 +44,11 @@ public:
 
   // Forward behaviour to wrapped thread pool implementation.
   NS_FORWARD_SAFE_NSITHREADPOOL(mPool);
-  NS_FORWARD_SAFE_NSIEVENTTARGET(mEventTarget);
+  NS_FORWARD_SAFE_NSIEVENTTARGET(GetEventTarget());
+
+  nsIEventTarget* GetEventTarget() {
+    return mEventTarget;
+  }
 
 private: