Mojo: More plumbing required to transfer handles over MessagePipes.

mojo/system/message_pipe_endpoint.h

 // Copyright 2013 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_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_
 #define MOJO_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 20 matching lines @@
 // dispatcher, e.g., to read messages and to wait. Implementations of this class
 // are not thread-safe; instances are protected by |MesssagePipe|'s lock.
 class MOJO_SYSTEM_EXPORT MessagePipeEndpoint {
  public:
   virtual ~MessagePipeEndpoint() {}
 
   // All implementations must implement these.
   virtual void Close() = 0;
   // Returns false if the endpoint should be closed and destroyed, else true.
   virtual bool OnPeerClose() = 0;
-  // Takes ownership of |message|.
-  virtual MojoResult EnqueueMessage(
+  // Checks if |EnqueueMessage()| will be able to enqueue the given message
+  // (with the given set of dispatchers). |dispatchers| should be non-null only
+  // if it's nonempty. Returns |MOJO_RESULT_OK| if it will and an appropriate
+  // error code if it won't.
+  virtual MojoResult CanEnqueueMessage(
+      const MessageInTransit* message,
+      const std::vector<Dispatcher*>* dispatchers) = 0;
+  // Takes ownership of |message| and the contents of |dispatchers| (leaving
+  // it empty). This should only be called after |CanEnqueueMessage()| has
+  // indicated success. (Unlike |CanEnqueueMessage()|, |dispatchers| may be
+  // non-null but empty.)
+  virtual void EnqueueMessage(
       MessageInTransit* message,
-      const std::vector<Dispatcher*>* dispatchers) = 0;
+      std::vector<scoped_refptr<Dispatcher> >* dispatchers) = 0;
 
   // Implementations must override these if they represent a local endpoint,
   // i.e., one for which there's a |MessagePipeDispatcher| (and thus a handle).
   // An implementation for a proxy endpoint (for which there's no dispatcher)
   // needs not override these methods, since they should never be called.
   //
   // These methods implement the methods of the same name in |MessagePipe|,
   // though |MessagePipe|'s implementation may have to do a little more if the
   // operation involves both endpoints.
   virtual void CancelAllWaiters();
@@ skipping 19 matching lines @@
   MessagePipeEndpoint() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MessagePipeEndpoint);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_