Support re-entrant calls to MessageQueueManager::Clear.

webrtc/rtc_base/messagequeue.h

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 52 matching lines @@
 
   void AddInternal(MessageQueue *message_queue);
   void RemoveInternal(MessageQueue *message_queue);
   void ClearInternal(MessageHandler *handler);
   void ProcessAllMessageQueuesInternal();
 
   static MessageQueueManager* instance_;
   // This list contains all live MessageQueues.
   std::vector<MessageQueue*> message_queues_ GUARDED_BY(crit_);
 
-  // Acquire this with DebugNonReentrantCritScope.
   CriticalSection crit_;
-  bool locked_ GUARDED_BY(crit_);
+  size_t processing_ GUARDED_BY(crit_);

[Taylor Brandstetter, 2017/07/05 22:41:47]

It would be nice if there was a comment describing the overall approach to
re-entrancy. Maybe here would be a good place?

[joachim, 2017/07/05 23:03:11]

Done.

 };
 
 // Derive from this for specialized data
 // App manages lifetime, except when messages are purged
 
 class MessageData {
  public:
   MessageData() {}
   virtual ~MessageData() {}
 };
@@ skipping 265 matching lines @@
   SocketServer* const ss_;
   // Used if SocketServer ownership lies with |this|.
   std::unique_ptr<SocketServer> own_ss_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(MessageQueue);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_RTC_BASE_MESSAGEQUEUE_H_