dom/media/MediaShutdownManager.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim:set ts=2 sw=2 sts=2 et cindent: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #if !defined(MediaShutdownManager_h_)
   8 #  define MediaShutdownManager_h_
   9
  10 #  include "mozilla/Monitor.h"
  11 #  include "mozilla/RefPtr.h"
  12 #  include "mozilla/StaticPtr.h"
  13 #  include "nsCOMPtr.h"
  14 #  include "nsIAsyncShutdown.h"
  15 #  include "nsIThread.h"
  16 #  include "nsTHashSet.h"
  17
  18 namespace mozilla {
  19
  20 class MediaDecoder;
  21
  22 // The MediaShutdownManager manages shutting down the MediaDecoder
  23 // infrastructure in response to an xpcom-shutdown notification.
  24 // This happens when Gecko is shutting down in the middle of operation.
  25 // This is tricky, as there are a number of moving parts that must
  26 // be shutdown in a particular order. The MediaShutdownManager
  27 // encapsulates all these dependencies to ensure that no shutdown
  28 // order dependencies leak out of the MediaDecoder stack.
  29 // The MediaShutdownManager is a singleton.
  30 //
  31 // The MediaShutdownManager ensures that the MediaDecoder stack
  32 // is shutdown before exiting xpcom-shutdown stage by registering
  33 // itself with nsIAsyncShutdownService to receive notification
  34 // when the stage of shutdown has started and then calls Shutdown()
  35 // on every MediaDecoder. Shutdown will not proceed until all
  36 // MediaDecoders finish shutdown and MediaShutdownManager unregisters
  37 // itself from the async shutdown service.
  38 //
  39 // Note that calling the Unregister() functions may result in the singleton
  40 // being deleted, so don't store references to the singleton, always use the
  41 // singleton by derefing the referenced returned by
  42 // MediaShutdownManager::Instance(), which ensures that the singleton is
  43 // created when needed.
  44 // i.e. like this:
  45 //    MediaShutdownManager::Instance()::Unregister(someDecoder);
  46 //    MediaShutdownManager::Instance()::Register(someOtherDecoder);
  47 // Not like this:
  48 //  MediaShutdownManager& instance = MediaShutdownManager::Instance();
  49 //  instance.Unregister(someDecoder); // Warning! May delete instance!
  50 //  instance.Register(someOtherDecoder); // BAD! instance may be dangling!
  51 class MediaShutdownManager : public nsIAsyncShutdownBlocker {
  52  public:
  53   NS_DECL_ISUPPORTS
  54   NS_DECL_NSIASYNCSHUTDOWNBLOCKER
  55
  56   static void InitStatics();
  57
  58   // The MediaShutdownManager is a singleton, access its instance with
  59   // this accessor.
  60   static MediaShutdownManager& Instance();
  61
  62   // Notifies the MediaShutdownManager that it needs to track the shutdown
  63   // of this MediaDecoder.
  64   nsresult Register(MediaDecoder* aDecoder);
  65
  66   // Notifies the MediaShutdownManager that a MediaDecoder that it was
  67   // tracking has shutdown, and it no longer needs to be shutdown in the
  68   // xpcom-shutdown listener.
  69   void Unregister(MediaDecoder* aDecoder);
  70
  71  private:
  72   enum InitPhase {
  73     NotInited,
  74     InitSucceeded,
  75     InitFailed,
  76     XPCOMShutdownStarted,
  77     XPCOMShutdownEnded
  78   };
  79
  80   static InitPhase sInitPhase;
  81
  82   MediaShutdownManager();
  83   virtual ~MediaShutdownManager();
  84   void RemoveBlocker();
  85
  86   static StaticRefPtr<MediaShutdownManager> sInstance;
  87
  88   // References to the MediaDecoder. The decoders unregister themselves
  89   // in their Shutdown() method, so we'll drop the reference naturally when
  90   // we're shutting down (in the non xpcom-shutdown case).
  91   nsTHashSet<RefPtr<MediaDecoder>> mDecoders;
  92 };
  93
  94 }  // namespace mozilla
  95
  96 #endif