nsHtml5StreamListener.h

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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 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