The Tor Browser: content/media/MediaShutdownManager.h@44a2da4a2ab2 (annotated)

content/media/MediaShutdownManager.h@44a2da4a2ab2 (annotated)

content/media/MediaShutdownManager.h

Fri, 16 Jan 2015 04:50:19 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Fri, 16 Jan 2015 04:50:19 +0100
branch: TOR_BUG_9701
changeset 13: 44a2da4a2ab2
permissions: -rw-r--r--

Replace accessor implementation with direct member state manipulation, by
request https://trac.torproject.org/projects/tor/ticket/9701#comment:32

 /* -*- 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

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content/media/MediaShutdownManager.h@44a2da4a2ab2 (annotated)

content/media/MediaShutdownManager.h