MediaShutdownManager.h

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/* -*- 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 "mozilla/Monitor.h"

#  include "mozilla/RefPtr.h"

#  include "mozilla/StaticPtr.h"

#  include "nsCOMPtr.h"

#  include "nsIAsyncShutdown.h"

#  include "nsIThread.h"

#  include "nsTHashSet.h"

namespace mozilla {

class MediaDecoder;

// 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. The MediaShutdownManager

// encapsulates all these dependencies 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 exiting xpcom-shutdown stage by registering

// itself with nsIAsyncShutdownService to receive notification

// when the stage of shutdown has started and then calls Shutdown()

// on every MediaDecoder. Shutdown will not proceed until all

// MediaDecoders finish shutdown and MediaShutdownManager unregisters

// itself from the async shutdown service.

//

// 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 nsIAsyncShutdownBlocker {

 public:

  NS_DECL_ISUPPORTS

  NS_DECL_NSIASYNCSHUTDOWNBLOCKER

  static void InitStatics();

  // 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.

  nsresult 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:

  enum InitPhase {

    NotInited,

    InitSucceeded,

    InitFailed,

    XPCOMShutdownStarted,

    XPCOMShutdownEnded

};

  static InitPhase sInitPhase;

  MediaShutdownManager();

  virtual ~MediaShutdownManager();

  void RemoveBlocker();

  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).

  nsTHashSet<RefPtr<MediaDecoder>> mDecoders;

};

}  // namespace mozilla

#endif