Fixing race between ~AsyncInvoker and ~AsyncClosure, using ref-counting.

webrtc/rtc_base/asyncinvoker-inl.h

 /*
  *  Copyright 2014 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_RTC_BASE_ASYNCINVOKER_INL_H_
 #define WEBRTC_RTC_BASE_ASYNCINVOKER_INL_H_
 
 #include "webrtc/rtc_base/atomicops.h"
 #include "webrtc/rtc_base/bind.h"
 #include "webrtc/rtc_base/criticalsection.h"
+#include "webrtc/rtc_base/event.h"
 #include "webrtc/rtc_base/messagehandler.h"
+#include "webrtc/rtc_base/refcountedobject.h"
+#include "webrtc/rtc_base/scoped_ref_ptr.h"
 #include "webrtc/rtc_base/sigslot.h"
 #include "webrtc/rtc_base/thread.h"
 #include "webrtc/rtc_base/thread_annotations.h"
 
 namespace rtc {
 
 class AsyncInvoker;
 
 // Helper class for AsyncInvoker. Runs a task and triggers a callback
 // on the calling thread if necessary.
 class AsyncClosure {
  public:
-  explicit AsyncClosure(AsyncInvoker* invoker) : invoker_(invoker) {}
+  explicit AsyncClosure(AsyncInvoker* invoker);
   virtual ~AsyncClosure();
   // Runs the asynchronous task, and triggers a callback to the calling
   // thread if needed. Should be called from the target thread.
   virtual void Execute() = 0;
 
  protected:
   AsyncInvoker* invoker_;
+  // Reference counted so that if the AsyncInvoker destructor finishes before
+  // an AsyncClosure's destructor that's about to call
+  // "invocation_complete_->Set()", it's not dereferenced after being
+  // destroyed.
+  scoped_refptr<RefCountedObject<Event>> invocation_complete_;
 };
 
 // Simple closure that doesn't trigger a callback for the calling thread.
 template <class FunctorT>
 class FireAndForgetAsyncClosure : public AsyncClosure {
  public:
   explicit FireAndForgetAsyncClosure(AsyncInvoker* invoker,
                                      const FunctorT& functor)
       : AsyncClosure(invoker), functor_(functor) {}
   virtual void Execute() {
     functor_();
   }
  private:
   FunctorT functor_;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_RTC_BASE_ASYNCINVOKER_INL_H_