gecko-dev/dom/media/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 "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;
// 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