Mojo: Add the ability to notify a Mojo Channel that it's going to be destroyed soon.

mojo/embedder/channel_init.h

 // Copyright 2014 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 MOJO_EMBEDDER_CHANNEL_INIT_H_
 #define MOJO_EMBEDDER_CHANNEL_INIT_H_
 
 #include "base/files/file.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "mojo/public/cpp/system/core.h"
 #include "mojo/system/system_impl_export.h"
 
 namespace base {
 class MessageLoopProxy;
 class TaskRunner;
 }
 
 namespace mojo {
 namespace embedder {
 struct ChannelInfo;
 }
 
 namespace embedder {
 
-// ChannelInit handle creation (and destruction) of the mojo channel. It is
-// expected that this class is created and destroyed on the main thread.
+// |ChannelInit| handles creation (and destruction) of the Mojo channel. It is
+// not thread-safe, but may be used on any single thread (with a |MessageLoop|).
 class MOJO_SYSTEM_IMPL_EXPORT ChannelInit {
  public:
   ChannelInit();
   ~ChannelInit();
 
   // Initializes the channel. This takes ownership of |file|. Returns the
   // primordial MessagePipe for the channel.
   mojo::ScopedMessagePipeHandle Init(
       base::PlatformFile file,
       scoped_refptr<base::TaskRunner> io_thread_task_runner);
 
+  // Notifies the channel that we (hence it) will soon be destroyed.
+  void WillDestroySoon();
+
  private:
-  // Invoked on the main thread once the channel has been established.
-  static void OnCreatedChannel(base::WeakPtr<ChannelInit> host,
+  // Invoked on the main thread once the channel has been established. (This is

[yzshen1, 2014/08/13 19:44:10]

nit: maybe it is good to clarify what main thread means here? (the single thread
that this object is used on)

+  // a static method that takes a weak pointer to self, since we want to destroy
+  // the channel even if we're destroyed.)
+  static void OnCreatedChannel(base::WeakPtr<ChannelInit> self,
                                scoped_refptr<base::TaskRunner> io_thread,
                                embedder::ChannelInfo* channel);
 
   scoped_refptr<base::TaskRunner> io_thread_task_runner_;
 
   // If non-null the channel has been established.
   embedder::ChannelInfo* channel_info_;
 
   base::WeakPtrFactory<ChannelInit> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ChannelInit);
 };
 
 }  // namespace embedder
 }  // namespace mojo
 
 #endif  // MOJO_EMBEDDER_CHANNEL_INIT_H_