зеркало из https://github.com/mozilla/gecko-dev.git
105 строки
4.2 KiB
C++
105 строки
4.2 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim:set ts=2 sw=2 sts=2 et cindent: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#if !defined(MediaShutdownManager_h_)
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#define MediaShutdownManager_h_
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#include "nsIObserver.h"
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#include "mozilla/Monitor.h"
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#include "mozilla/RefPtr.h"
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#include "mozilla/StaticPtr.h"
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#include "nsIThread.h"
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#include "nsCOMPtr.h"
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#include "nsTHashtable.h"
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#include "nsHashKeys.h"
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namespace mozilla {
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class MediaDecoder;
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// The MediaShutdownManager manages shutting down the MediaDecoder
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// infrastructure in response to an xpcom-shutdown notification. This happens
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// when Gecko is shutting down in the middle of operation. This is tricky, as
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// there are a number of moving parts that must be shutdown in a particular
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// order. Additionally the xpcom-shutdown observer *must* block until all
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// threads are shutdown, which is tricky since we have a number of threads
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// here and their shutdown is asynchronous. We can't have each element of
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// our pipeline listening for xpcom-shutdown, as if each observer blocks
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// waiting for its threads to shutdown it will block other xpcom-shutdown
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// notifications from firing, and shutdown of one part of the media pipeline
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// (say the State Machine thread) may depend another part to be shutdown
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// first (the MediaDecoder threads). The MediaShutdownManager encapsulates
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// all these dependencies, and provides a single xpcom-shutdown listener
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// for the MediaDecoder infrastructure, to ensure that no shutdown order
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// dependencies leak out of the MediaDecoder stack. The MediaShutdownManager
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// is a singleton.
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//
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// The MediaShutdownManager ensures that the MediaDecoder stack is shutdown
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// before returning from its xpcom-shutdown observer by keeping track of all
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// the active MediaDecoders, and upon xpcom-shutdown calling Shutdown() on
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// every MediaDecoder and then spinning the main thread event loop until all
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// SharedThreadPools have shutdown. Once the SharedThreadPools are shutdown,
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// all the state machines and their threads have been shutdown, the
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// xpcom-shutdown observer returns.
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//
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// Note that calling the Unregister() functions may result in the singleton
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// being deleted, so don't store references to the singleton, always use the
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// singleton by derefing the referenced returned by
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// MediaShutdownManager::Instance(), which ensures that the singleton is
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// created when needed.
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// i.e. like this:
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// MediaShutdownManager::Instance()::Unregister(someDecoder);
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// MediaShutdownManager::Instance()::Register(someOtherDecoder);
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// Not like this:
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// MediaShutdownManager& instance = MediaShutdownManager::Instance();
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// instance.Unregister(someDecoder); // Warning! May delete instance!
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// instance.Register(someOtherDecoder); // BAD! instance may be dangling!
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class MediaShutdownManager : public nsIObserver {
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public:
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NS_DECL_ISUPPORTS
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NS_DECL_NSIOBSERVER
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// The MediaShutdownManager is a singleton, access its instance with
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// this accessor.
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static MediaShutdownManager& Instance();
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// Notifies the MediaShutdownManager that it needs to track the shutdown
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// of this MediaDecoder.
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void Register(MediaDecoder* aDecoder);
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// Notifies the MediaShutdownManager that a MediaDecoder that it was
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// tracking has shutdown, and it no longer needs to be shutdown in the
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// xpcom-shutdown listener.
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void Unregister(MediaDecoder* aDecoder);
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private:
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MediaShutdownManager();
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virtual ~MediaShutdownManager();
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void Shutdown();
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// Ensures we have a shutdown listener if we need one, and removes the
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// listener and destroys the singleton if we don't.
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void EnsureCorrectShutdownObserverState();
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static StaticRefPtr<MediaShutdownManager> sInstance;
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// References to the MediaDecoder. The decoders unregister themselves
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// in their Shutdown() method, so we'll drop the reference naturally when
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// we're shutting down (in the non xpcom-shutdown case).
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nsTHashtable<nsRefPtrHashKey<MediaDecoder>> mDecoders;
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// True if we have an XPCOM shutdown observer.
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bool mIsObservingShutdown;
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bool mIsDoingXPCOMShutDown;
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};
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} // namespace mozilla
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#endif
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