Mojo: First stab at making MessagePipes work across OS pipes.

mojo/system/channel.h

Index: mojo/system/channel.h
diff --git a/mojo/system/channel.h b/mojo/system/channel.h
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+// 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_CHANNEL_H_
+#define MOJO_SYSTEM_CHANNEL_H_
+
+#include <stdint.h>
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/containers/hash_tables.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/strings/string_piece.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+#include "mojo/public/system/core.h"
+#include "mojo/public/system/system_export.h"
+#include "mojo/system/message_in_transit.h"
+#include "mojo/system/message_pipe.h"
+#include "mojo/system/raw_channel.h"
+
+namespace base {
+class MessageLoop;
+}
+
+namespace mojo {
+namespace system {
+
+// This class is mostly thread-safe. It must be created on an "I/O thread" (see
+// raw_channel.h). |Init()| must be called on that same thread before it becomes
+// thread-safe (in particular, before references are given to any other thread)
+// and |Shutdown()| must be called on that same thread before destruction. Its
+// public methods are otherwise thread-safe. It may be destroyed on any thread,
+// in the sense that the last reference to it may be released on any thread,
+// with the proviso that |Shutdown()| must have been called first (so the
+// pattern is that a "main" reference is kept on its creation thread and is
+// released after |Shutdown()| is called, but other threads may have temporarily
+// "dangling" references).
+//
+// Note that |MessagePipe| calls into |Channel| and the former's |lock_| must be
+// acquired before the latter's. When |Channel| wants to call into a
+// |MessagePipe|, it must obtain a reference to the |MessagePipe| (from
+// |local_id_to_endpoint_info_map_|) under |Channel::lock_| and then release the
+// lock.
+//
+// Also, care must be taken with respect to references: While a |Channel| has
+// references to |MessagePipe|s, |MessagePipe|s (via |ProxyMessagePipeEndpoint|)
+// may also have references to |Channel|s. These references are set up by
+// calling |AttachMessagePipeEndpoint()|. The reference to |MessagePipe| owned
+// by |Channel| must be removed by calling |DetachMessagePipeEndpoint()| (which
+// is done by |MessagePipe|/|ProxyMessagePipeEndpoint|, which simultaneously
+// removes its reference to |Channel|).
+class MOJO_SYSTEM_EXPORT Channel : public base::RefCountedThreadSafe<Channel>,
+                                   public RawChannel::Delegate {
+ public:
+  // The first message pipe endpoint attached will have this as its local ID.
+  static const MessageInTransit::EndpointId kBootstrapEndpointId = 1;
+
+  Channel();
+
+  // This must be called on the creation thread before any other methods are
+  // called, and before references to this object are given to any other
+  // threads. Takes ownership of |handle|. Returns true on success. On failure,
+  // no other methods should be called (including |Shutdown()|).
+  bool Init(const PlatformChannelHandle& handle);
+
+  // This must be called on the creation thread before destruction (which can
+  // happen on any thread).
+  void Shutdown();
+
+  // Attaches the given message pipe/port's endpoint (which must be a
+  // |ProxyMessagePipeEndpoint|) to this channel. This assigns it a local ID,
+  // which it returns. The first message pipe endpoint attached will always have
+  // |kBootstrapEndpointId| as its local ID. (For bootstrapping, this occurs on
+  // both sides, so one should use |kBootstrapEndpointId| for the remote ID for
+  // the first message pipe across a channel.)
+  MessageInTransit::EndpointId AttachMessagePipeEndpoint(
+      scoped_refptr<MessagePipe> message_pipe, unsigned port);
+  void RunMessagePipeEndpoint(MessageInTransit::EndpointId local_id,
+                              MessageInTransit::EndpointId remote_id);
+
+  // This forwards |message| verbatim to |raw_channel_|.
+  bool WriteMessage(MessageInTransit* message);
+
+  // This removes the message pipe/port's endpoint (with the given local ID,
+  // returned by |AttachMessagePipeEndpoint()| from this channel. After this is
+  // called, |local_id| may be reused for another message pipe.
+  void DetachMessagePipeEndpoint(MessageInTransit::EndpointId local_id);
+
+ private:
+  friend class base::RefCountedThreadSafe<Channel>;
+  virtual ~Channel();
+
+  // |RawChannel::Delegate| implementation:
+  virtual void OnReadMessage(const MessageInTransit& message) OVERRIDE;
+  virtual void OnFatalError(FatalError fatal_error) OVERRIDE;
+
+  // Helpers for |OnReadMessage|:
+  void OnReadMessageForDownstream(const MessageInTransit& message);
+  void OnReadMessageForChannel(const MessageInTransit& message);
+
+  // Handles errors (e.g., invalid messages) from the remote side.
+  void HandleRemoteError(const base::StringPiece& error_message);
+  // Handles internal errors/failures from the local side.
+  void HandleLocalError(const base::StringPiece& error_message);
+
+  struct EndpointInfo {
+    EndpointInfo();
+    EndpointInfo(scoped_refptr<MessagePipe> message_pipe, unsigned port);
+    ~EndpointInfo();
+
+    scoped_refptr<MessagePipe> message_pipe;
+    unsigned port;
+  };
+
+  base::ThreadChecker creation_thread_checker_;
+
+  // Note: |MessagePipe|s MUST NOT be used under |lock_|. I.e., |lock_| can only
+  // be acquired after |MessagePipe::lock_|, never before. Thus to call into a
+  // |MessagePipe|, a reference should be acquired from
+  // |local_id_to_endpoint_info_map_| under |lock_| (e.g., by copying the
+  // |EndpointInfo|) and then the lock released.
+  base::Lock lock_;  // Protects the members below.
+
+  scoped_ptr<RawChannel> raw_channel_;
+
+  typedef base::hash_map<MessageInTransit::EndpointId, EndpointInfo>
+      IdToEndpointInfoMap;
+  IdToEndpointInfoMap local_id_to_endpoint_info_map_;
+  // The next local ID to try (when allocating new local IDs). Note: It should
+  // be checked for existence before use.
+  MessageInTransit::EndpointId next_local_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(Channel);
+};
+
+}  // namespace system
+}  // namespace mojo
+
+#endif  // MOJO_SYSTEM_CHANNEL_H_