diff -r 000000000000 -r 6474c204b198 content/media/MediaShutdownManager.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/content/media/MediaShutdownManager.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,105 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#if !defined(MediaShutdownManager_h_)
+#define MediaShutdownManager_h_
+
+#include "nsIObserver.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/StaticPtr.h"
+#include "nsIThread.h"
+#include "nsCOMPtr.h"
+#include "nsTHashtable.h"
+#include "nsHashKeys.h"
+
+namespace mozilla {
+
+class MediaDecoder;
+class StateMachineThread;
+
+// The MediaShutdownManager manages shutting down the MediaDecoder
+// infrastructure in response to an xpcom-shutdown notification. This happens
+// when Gecko is shutting down in the middle of operation. This is tricky, as
+// there are a number of moving parts that must be shutdown in a particular
+// order. Additionally the xpcom-shutdown observer *must* block until all
+// threads are shutdown, which is tricky since we have a number of threads
+// here and their shutdown is asynchronous. We can't have each element of
+// our pipeline listening for xpcom-shutdown, as if each observer blocks
+// waiting for its threads to shutdown it will block other xpcom-shutdown
+// notifications from firing, and shutdown of one part of the media pipeline
+// (say the State Machine thread) may depend another part to be shutdown
+// first (the MediaDecoder threads). The MediaShutdownManager encapsulates
+// all these dependencies, and provides a single xpcom-shutdown listener
+// for the MediaDecoder infrastructure, to ensure that no shutdown order
+// dependencies leak out of the MediaDecoder stack. The MediaShutdownManager
+// is a singleton.
+//
+// The MediaShutdownManager ensures that the MediaDecoder stack is shutdown
+// before returning from its xpcom-shutdown observer by keeping track of all
+// the active MediaDecoders, and upon xpcom-shutdown calling Shutdown() on
+// every MediaDecoder and then spinning the main thread event loop until all
+// SharedThreadPools have shutdown. Once the SharedThreadPools are shutdown,
+// all the state machines and their threads have been shutdown, the
+// xpcom-shutdown observer returns.
+//
+// Note that calling the Unregister() functions may result in the singleton
+// being deleted, so don't store references to the singleton, always use the
+// singleton by derefing the referenced returned by
+// MediaShutdownManager::Instance(), which ensures that the singleton is
+// created when needed.
+// i.e. like this:
+//    MediaShutdownManager::Instance()::Unregister(someDecoder);
+//    MediaShutdownManager::Instance()::Register(someOtherDecoder);
+// Not like this:
+//  MediaShutdownManager& instance = MediaShutdownManager::Instance();
+//  instance.Unregister(someDecoder); // Warning! May delete instance!
+//  instance.Register(someOtherDecoder); // BAD! instance may be dangling!
+class MediaShutdownManager : public nsIObserver {
+public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  // The MediaShutdownManager is a singleton, access its instance with
+  // this accessor.
+  static MediaShutdownManager& Instance();
+
+  // Notifies the MediaShutdownManager that it needs to track the shutdown
+  // of this MediaDecoder.
+  void Register(MediaDecoder* aDecoder);
+
+  // Notifies the MediaShutdownManager that a MediaDecoder that it was
+  // tracking has shutdown, and it no longer needs to be shutdown in the
+  // xpcom-shutdown listener.
+  void Unregister(MediaDecoder* aDecoder);
+
+private:
+
+  MediaShutdownManager();
+  virtual ~MediaShutdownManager();
+
+  void Shutdown();
+
+  // Ensures we have a shutdown listener if we need one, and removes the
+  // listener and destroys the singleton if we don't.
+  void EnsureCorrectShutdownObserverState();
+
+  static StaticRefPtr<MediaShutdownManager> sInstance;
+
+  // References to the MediaDecoder. The decoders unregister themselves
+  // in their Shutdown() method, so we'll drop the reference naturally when
+  // we're shutting down (in the non xpcom-shutdown case).
+  nsTHashtable<nsRefPtrHashKey<MediaDecoder>> mDecoders;
+
+  // True if we have an XPCOM shutdown observer.
+  bool mIsObservingShutdown;
+
+  bool mIsDoingXPCOMShutDown;
+};
+
+} // namespace mozilla
+
+#endif