forked from mirrors/gecko-dev
827cd75825
Depends on D187668 Differential Revision: https://phabricator.services.mozilla.com/D187689
61 lines
2.5 KiB
C++
61 lines
2.5 KiB
C++
/* 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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#ifndef nsHtml5StreamListener_h
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#define nsHtml5StreamListener_h
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#include "nsIStreamListener.h"
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#include "nsIThreadRetargetableStreamListener.h"
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#include "nsHtml5StreamParser.h"
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#include "mozilla/ReentrantMonitor.h"
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/**
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* The purpose of this class is to reconcile the problem that
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* nsHtml5StreamParser is a cycle collection participant, which means that it
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* can only be refcounted on the main thread, but
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* nsIThreadRetargetableStreamListener can be refcounted from another thread,
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* so nsHtml5StreamParser being an nsIThreadRetargetableStreamListener was
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* a memory corruption problem.
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*
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* mDelegate is an nsHtml5StreamParserPtr, which releases the object that it
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* points to from a runnable on the main thread. DropDelegate() is only called
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* on the main thread. This call will finish before the main-thread derefs the
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* nsHtml5StreamListener itself, so there is no risk of another thread making
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* the refcount of nsHtml5StreamListener go to zero and running the destructor
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* concurrently. Other than that, the thread-safe nsISupports implementation
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* takes care of the destructor not running concurrently from different
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* threads, so there is no need to have a mutex around nsHtml5StreamParserPtr to
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* prevent it from double-releasing nsHtml5StreamParser.
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*/
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class nsHtml5StreamListener : public nsIThreadRetargetableStreamListener {
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public:
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explicit nsHtml5StreamListener(nsHtml5StreamParser* aDelegate);
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NS_DECL_THREADSAFE_ISUPPORTS
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NS_DECL_NSIREQUESTOBSERVER
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NS_DECL_NSISTREAMLISTENER
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NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
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// Main-thread-only
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nsHtml5StreamParser* GetDelegate();
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// Main-thread-only
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void DropDelegate();
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private:
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void DropDelegateImpl();
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virtual ~nsHtml5StreamListener();
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// ReentrantMonitor instead of Mutex, because `GetDelegate()`
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// can be called from within the Necko callbacks when Necko events
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// are delivered on the main thread.
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mozilla::ReentrantMonitor mDelegateMonitor MOZ_UNANNOTATED;
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// Owning pointer with manually-managed refcounting, protected by
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// mDelegateMonitor. Access to it is Atomic, which avoids getting a lock
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// to check if it's set or to return the pointer. Access to the data within
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// it needs the monitor. MOZ_PT_GUARDED_BY() can't be used with Atomic<...*>
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mozilla::Atomic<nsHtml5StreamParser*, mozilla::ReleaseAcquire> mDelegate;
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};
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#endif // nsHtml5StreamListener_h
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