1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/content/media/MediaShutdownManager.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,105 @@
1.4 +/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
1.5 +/* vim:set ts=2 sw=2 sts=2 et cindent: */
1.6 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +#if !defined(MediaShutdownManager_h_)
1.11 +#define MediaShutdownManager_h_
1.12 +
1.13 +#include "nsIObserver.h"
1.14 +#include "mozilla/Monitor.h"
1.15 +#include "mozilla/RefPtr.h"
1.16 +#include "mozilla/StaticPtr.h"
1.17 +#include "nsIThread.h"
1.18 +#include "nsCOMPtr.h"
1.19 +#include "nsTHashtable.h"
1.20 +#include "nsHashKeys.h"
1.21 +
1.22 +namespace mozilla {
1.23 +
1.24 +class MediaDecoder;
1.25 +class StateMachineThread;
1.26 +
1.27 +// The MediaShutdownManager manages shutting down the MediaDecoder
1.28 +// infrastructure in response to an xpcom-shutdown notification. This happens
1.29 +// when Gecko is shutting down in the middle of operation. This is tricky, as
1.30 +// there are a number of moving parts that must be shutdown in a particular
1.31 +// order. Additionally the xpcom-shutdown observer *must* block until all
1.32 +// threads are shutdown, which is tricky since we have a number of threads
1.33 +// here and their shutdown is asynchronous. We can't have each element of
1.34 +// our pipeline listening for xpcom-shutdown, as if each observer blocks
1.35 +// waiting for its threads to shutdown it will block other xpcom-shutdown
1.36 +// notifications from firing, and shutdown of one part of the media pipeline
1.37 +// (say the State Machine thread) may depend another part to be shutdown
1.38 +// first (the MediaDecoder threads). The MediaShutdownManager encapsulates
1.39 +// all these dependencies, and provides a single xpcom-shutdown listener
1.40 +// for the MediaDecoder infrastructure, to ensure that no shutdown order
1.41 +// dependencies leak out of the MediaDecoder stack. The MediaShutdownManager
1.42 +// is a singleton.
1.43 +//
1.44 +// The MediaShutdownManager ensures that the MediaDecoder stack is shutdown
1.45 +// before returning from its xpcom-shutdown observer by keeping track of all
1.46 +// the active MediaDecoders, and upon xpcom-shutdown calling Shutdown() on
1.47 +// every MediaDecoder and then spinning the main thread event loop until all
1.48 +// SharedThreadPools have shutdown. Once the SharedThreadPools are shutdown,
1.49 +// all the state machines and their threads have been shutdown, the
1.50 +// xpcom-shutdown observer returns.
1.51 +//
1.52 +// Note that calling the Unregister() functions may result in the singleton
1.53 +// being deleted, so don't store references to the singleton, always use the
1.54 +// singleton by derefing the referenced returned by
1.55 +// MediaShutdownManager::Instance(), which ensures that the singleton is
1.56 +// created when needed.
1.57 +// i.e. like this:
1.58 +// MediaShutdownManager::Instance()::Unregister(someDecoder);
1.59 +// MediaShutdownManager::Instance()::Register(someOtherDecoder);
1.60 +// Not like this:
1.61 +// MediaShutdownManager& instance = MediaShutdownManager::Instance();
1.62 +// instance.Unregister(someDecoder); // Warning! May delete instance!
1.63 +// instance.Register(someOtherDecoder); // BAD! instance may be dangling!
1.64 +class MediaShutdownManager : public nsIObserver {
1.65 +public:
1.66 + NS_DECL_ISUPPORTS
1.67 + NS_DECL_NSIOBSERVER
1.68 +
1.69 + // The MediaShutdownManager is a singleton, access its instance with
1.70 + // this accessor.
1.71 + static MediaShutdownManager& Instance();
1.72 +
1.73 + // Notifies the MediaShutdownManager that it needs to track the shutdown
1.74 + // of this MediaDecoder.
1.75 + void Register(MediaDecoder* aDecoder);
1.76 +
1.77 + // Notifies the MediaShutdownManager that a MediaDecoder that it was
1.78 + // tracking has shutdown, and it no longer needs to be shutdown in the
1.79 + // xpcom-shutdown listener.
1.80 + void Unregister(MediaDecoder* aDecoder);
1.81 +
1.82 +private:
1.83 +
1.84 + MediaShutdownManager();
1.85 + virtual ~MediaShutdownManager();
1.86 +
1.87 + void Shutdown();
1.88 +
1.89 + // Ensures we have a shutdown listener if we need one, and removes the
1.90 + // listener and destroys the singleton if we don't.
1.91 + void EnsureCorrectShutdownObserverState();
1.92 +
1.93 + static StaticRefPtr<MediaShutdownManager> sInstance;
1.94 +
1.95 + // References to the MediaDecoder. The decoders unregister themselves
1.96 + // in their Shutdown() method, so we'll drop the reference naturally when
1.97 + // we're shutting down (in the non xpcom-shutdown case).
1.98 + nsTHashtable<nsRefPtrHashKey<MediaDecoder>> mDecoders;
1.99 +
1.100 + // True if we have an XPCOM shutdown observer.
1.101 + bool mIsObservingShutdown;
1.102 +
1.103 + bool mIsDoingXPCOMShutDown;
1.104 +};
1.105 +
1.106 +} // namespace mozilla
1.107 +
1.108 +#endif
