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