Implementation of PostTaskAndReply() in MessageLoopProxy and BrowserThread.

base/task.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_TASK_H_
 #define BASE_TASK_H_
 #pragma once
 
 #include "base/base_export.h"
+#include "base/callback.h"
 #include "base/debug/alias.h"
 #include "base/memory/raw_scoped_refptr_mismatch_checker.h"
 #include "base/memory/weak_ptr.h"
 #include "base/tracked.h"
 #include "base/tuple.h"
 
 namespace base {
 const size_t kDeadTask = 0xDEAD7A53;
+class MessageLoopProxy;
 }
 
 // Task ------------------------------------------------------------------------
 //
 // A task is a generic runnable thingy, usually used for running code on a
 // different thread or for scheduling future tasks off of the message loop.
 
 class BASE_EXPORT Task : public tracked_objects::Tracked {
  public:
   Task();
@@ skipping 567 matching lines @@
 
   ~TaskClosureAdapter();
 
   Task* task_;
   bool* should_leak_task_;
   static bool kTaskLeakingDefault;
 };
 
 }  // namespace subtle
 
+namespace internal {
+
+// This relay class remembers the MessageLoop that it was created on, and
+// ensures that both the |task| and |reply| Closures are deleted on this same
+// thread. Also, |task| is guaranteed to be deleted before |reply| is run or
+// deleted.
+//
+// If this is not possible because the originating MessageLoop is no longer
+// available, the the |task| and |reply| Closures are leaked.  Leaking is
+// considered preferable to having a thread-safetey violations caused by
+// invoking the Closure destructor on the wrong thread.
+class PostTaskAndReplyRelay {
+ public:
+  PostTaskAndReplyRelay(const tracked_objects::Location& from_here,
+                        const Closure& task, const Closure& reply);
+
+  ~PostTaskAndReplyRelay();
+
+  void Run();
+
+ private:
+  void RunReplyAndSelfDestruct();
+
+  tracked_objects::Location from_here_;
+  scoped_refptr<MessageLoopProxy> origin_loop_;
+  Closure reply_;
+  Closure task_;
+};
+
+}  // namespace internal
+
 }  // namespace base
 
 #endif  // BASE_TASK_H_