Fix potential deadlock in TaskQueue's libevent PostTaskAndReply implementation

webrtc/base/task_queue.h

 /*
  *  Copyright 2016 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.
  */
 
 #ifndef WEBRTC_BASE_TASK_QUEUE_H_
 #define WEBRTC_BASE_TASK_QUEUE_H_
 
 #include <list>
 #include <memory>
 #include <unordered_map>
 
 #if defined(WEBRTC_MAC) && !defined(WEBRTC_BUILD_LIBEVENT)
 #include <dispatch/dispatch.h>
 #endif
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/criticalsection.h"
 
 #if defined(WEBRTC_WIN) || defined(WEBRTC_BUILD_LIBEVENT)
 #include "webrtc/base/platform_thread.h"
 #endif
 
 #if defined(WEBRTC_BUILD_LIBEVENT)
+#include "webrtc/base/refcountedobject.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+
 struct event_base;
 struct event;
 #endif
 
 namespace rtc {
 
 // Base interface for asynchronously executed tasks.
 // The interface basically consists of a single function, Run(), that executes
 // on the target queue.  For more details see the Run() method and TaskQueue.
 class QueuedTask {
@@ skipping 190 matching lines @@
         std::unique_ptr<QueuedTask>(new ClosureTask<Closure2>(reply)));
   }
 
  private:
 #if defined(WEBRTC_BUILD_LIBEVENT)
   static bool ThreadMain(void* context);
   static void OnWakeup(int socket, short flags, void* context);  // NOLINT
   static void RunTask(int fd, short flags, void* context);       // NOLINT
   static void RunTimer(int fd, short flags, void* context);      // NOLINT
 
+  class ReplyTaskOwner;
   class PostAndReplyTask;
   class SetTimerTask;
 
-  void PrepareReplyTask(PostAndReplyTask* reply_task);
-  void ReplyTaskDone(PostAndReplyTask* reply_task);
+  typedef RefCountedObject<ReplyTaskOwner> ReplyTaskOwnerRef;
+
+  void PrepareReplyTask(scoped_refptr<ReplyTaskOwnerRef> reply_task);
 
   struct QueueContext;
 
   int wakeup_pipe_in_ = -1;
   int wakeup_pipe_out_ = -1;
   event_base* event_base_;
   std::unique_ptr<event> wakeup_event_;
   PlatformThread thread_;
   rtc::CriticalSection pending_lock_;
   std::list<std::unique_ptr<QueuedTask>> pending_ GUARDED_BY(pending_lock_);
-  std::list<PostAndReplyTask*> pending_replies_ GUARDED_BY(pending_lock_);
+  std::list<scoped_refptr<ReplyTaskOwnerRef>> pending_replies_
+      GUARDED_BY(pending_lock_);
 #elif defined(WEBRTC_MAC)
   struct QueueContext;
   struct TaskContext;
   struct PostTaskAndReplyContext;
   dispatch_queue_t queue_;
   QueueContext* const context_;
 #elif defined(WEBRTC_WIN)
   class MultimediaTimer;
   typedef std::unordered_map<UINT_PTR, std::unique_ptr<QueuedTask>>
       DelayedTasks;
@@ skipping 14 matching lines @@
 #else
 #error not supported.
 #endif
 
   RTC_DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_TASK_QUEUE_H_