Mojo: Abstract out the endpoints of 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 "base/basictypes.h"
+#include "mojo/public/system/core.h"
+
+namespace mojo {
+namespace system {
+
+class Waiter;
+
+// This is an interface to one of the ends of a message pipe, and is used by
+// |MessagePipe|. Its most important role is to provide a sink for messages
+// (i.e., a place where messages can be sent). It has a secondary role: When the
+// endpoint is local (i.e., in the current process), there'll be a dispatcher
+// corresponding to the endpoint, and |MessagePipeEndpoint| also implements the

[darin (slow to review), 2013/10/15 06:50:36]

nit: Is the comment "|MessagePipeEndpoint| also implements the requisite
functionality, e.g., to read messages and to wait" accurate? It doesn't seem to
provide interesting implementations of those functions. They are on
LocalMessagePipeEndpoint.

[viettrungluu, 2013/10/15 17:48:58]

Errr, "the implementation of |MessagePipeEndpoint|". I tried to make the comment
a little more clear.

+// requisite functionality, e.g., to read messages and to wait. This class is
+// not thread-safe; instances are protected by |MesssagePipe|'s lock.
+class MessagePipeEndpoint {
+ public:
+  virtual ~MessagePipeEndpoint() {}
+
+  // All implementations must implement these.
+  virtual void OnPeerClose() = 0;
+  virtual MojoResult EnqueueMessage(
+      const void* bytes, uint32_t num_bytes,
+      const MojoHandle* handles, uint32_t num_handles,
+      MojoWriteMessageFlags flags) = 0;
+
+  // Implementations must implement/override these if they are "connected" to a
+  // local |MessagePipeDispatcher| (the default implementations should never be

[darin (slow to review), 2013/10/15 06:50:36]

I'm having trouble following this design. Are you saying that when connected to
a non-local MessagePipeDispatcher that these methods may not be implemented /
overridden? What does that mean?

[viettrungluu, 2013/10/15 17:48:58]

A MessagePipeDispatcher corresponds to a handle, so in the remote (non-local)
case, there's no MessagePipeDispatcher (locally) and thus nothing to call these
methods.

I've tried to make the comments a little more clear.

+  // called). They 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();
+  virtual void Close();
+  virtual MojoResult ReadMessage(void* bytes, uint32_t* num_bytes,
+                                 MojoHandle* handles, uint32_t* num_handles,
+                                 MojoReadMessageFlags flags);
+  virtual MojoResult AddWaiter(Waiter* waiter,
+                               MojoWaitFlags flags,
+                               MojoResult wake_result);
+  virtual void RemoveWaiter(Waiter* waiter);
+
+ protected:
+  MessagePipeEndpoint() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MessagePipeEndpoint);
+};
+
+}  // namespace system
+}  // namespace mojo
+
+#endif  // MOJO_SYSTEM_MESSAGE_PIPE_ENDPOINT_H_