Fix/reland 505555fa8031fc06d67e9ed43e3021d8d84cb44f (crrev.com/773983002).

mojo/edk/system/channel_endpoint.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_EDK_SYSTEM_CHANNEL_ENDPOINT_H_
 #define MOJO_EDK_SYSTEM_CHANNEL_ENDPOINT_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 112 matching lines @@
                   unsigned client_port,
                   MessageInTransitQueue* message_queue = nullptr);
 
   // Methods called by |ChannelEndpointClient|:
 
   // Called to enqueue an outbound message. (If |AttachAndRun()| has not yet
   // been called, the message will be enqueued and sent when |AttachAndRun()| is
   // called.)
   bool EnqueueMessage(scoped_ptr<MessageInTransit> message);
 
+  // Called to *replace* current client with a new client (which must differ
+  // from the existing client). This must not be called after
+  // |DetachFromClient()| has been called.
+  //
+  // This returns true in the typical case, and false if this endpoint has been
+  // detached from the channel, in which case the caller should probably call
+  // its (new) client's |OnDetachFromChannel()|.
+  bool ReplaceClient(ChannelEndpointClient* client, unsigned client_port);
+
   // Called before the |ChannelEndpointClient| gives up its reference to this
   // object.
   void DetachFromClient();
 
   // Methods called by |Channel|:
 
   // Called when the |Channel| takes a reference to this object. This will send
   // all queue messages (in |channel_message_queue_|).
   // TODO(vtl): Maybe rename this "OnAttach"?
   void AttachAndRun(Channel* channel,
                     ChannelEndpointId local_id,
                     ChannelEndpointId remote_id);
 
   // Called when the |Channel| receives a message for the |ChannelEndpoint|.
   void OnReadMessage(scoped_ptr<MessageInTransit> message);
 
   // Called before the |Channel| gives up its reference to this object.
   void DetachFromChannel();
 
  private:
   friend class base::RefCountedThreadSafe<ChannelEndpoint>;
   ~ChannelEndpoint();
 
   // Must be called with |lock_| held.
   bool WriteMessageNoLock(scoped_ptr<MessageInTransit> message);
 
+  // Resets |channel_| to null (and sets |is_detached_from_channel_|). This may
+  // only be called if |channel_| is non-null. Must be called with |lock_| held.
+  void ResetChannelNoLock();
+
   // Protects the members below.
   base::Lock lock_;
 
   // |client_| must be valid whenever it is non-null. Before |*client_| gives up
   // its reference to this object, it must call |DetachFromClient()|.
   // NOTE: This is a |scoped_refptr<>|, rather than a raw pointer, since the
   // |Channel| needs to keep the |MessagePipe| alive for the "proxy-proxy" case.
   // Possibly we'll be able to eliminate that case when we have full
   // multiprocess support.
   // WARNING: |ChannelEndpointClient| methods must not be called under |lock_|.
   // Thus to make such a call, a reference must first be taken under |lock_| and
   // the lock released.
+  // WARNING: Beware of interactions with |ReplaceClient()|. By the time the
+  // call is made, the client may have changed. This must be detected and dealt
+  // with.
   scoped_refptr<ChannelEndpointClient> client_;
   unsigned client_port_;
 
   // |channel_| must be valid whenever it is non-null. Before |*channel_| gives
   // up its reference to this object, it must call |DetachFromChannel()|.
   // |local_id_| and |remote_id_| are valid if and only |channel_| is non-null.
   Channel* channel_;
   ChannelEndpointId local_id_;
   ChannelEndpointId remote_id_;
+  // This distinguishes the two cases of |channel| being null: not yet attached
+  // versus detached.
+  bool is_detached_from_channel_;
 
   // This queue is used before we're running on a channel and ready to send
   // messages to the channel.
   MessageInTransitQueue channel_message_queue_;
 
   DISALLOW_COPY_AND_ASSIGN(ChannelEndpoint);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_CHANNEL_ENDPOINT_H_