Separates ipc code from common (http://crbug.com/16829)

ipc/ipc_channel_proxy.h

+// Copyright (c) 2006-2008 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 IPC_IPC_CHANNEL_PROXY_H__
+#define IPC_IPC_CHANNEL_PROXY_H__
+
+#include <vector>
+
+#include "base/ref_counted.h"
+#include "ipc/ipc_channel.h"
+
+class MessageLoop;
+
+namespace IPC {
+
+//-----------------------------------------------------------------------------
+// IPC::ChannelProxy
+//
+// This class is a helper class that is useful when you wish to run an IPC
+// channel on a background thread.  It provides you with the option of either
+// handling IPC messages on that background thread or having them dispatched to
+// your main thread (the thread on which the IPC::ChannelProxy is created).
+//
+// The API for an IPC::ChannelProxy is very similar to that of an IPC::Channel.
+// When you send a message to an IPC::ChannelProxy, the message is routed to
+// the background thread, where it is then passed to the IPC::Channel's Send
+// method.  This means that you can send a message from your thread and your
+// message will be sent over the IPC channel when possible instead of being
+// delayed until your thread returns to its message loop.  (Often IPC messages
+// will queue up on the IPC::Channel when there is a lot of traffic, and the
+// channel will not get cycles to flush its message queue until the thread, on
+// which it is running, returns to its message loop.)
+//
+// An IPC::ChannelProxy can have a MessageFilter associated with it, which will
+// be notified of incoming messages on the IPC::Channel's thread.  This gives
+// the consumer of IPC::ChannelProxy the ability to respond to incoming
+// messages on this background thread instead of on their own thread, which may
+// be bogged down with other processing.  The result can be greatly improved
+// latency for messages that can be handled on a background thread.
+//
+// The consumer of IPC::ChannelProxy is responsible for allocating the Thread
+// instance where the IPC::Channel will be created and operated.
+//
+class ChannelProxy : public Message::Sender {
+ public:
+  // A class that receives messages on the thread where the IPC channel is
+  // running.  It can choose to prevent the default action for an IPC message.
+  class MessageFilter : public base::RefCountedThreadSafe<MessageFilter> {
+   public:
+    virtual ~MessageFilter() {}
+
+    // Called on the background thread to provide the filter with access to the
+    // channel.  Called when the IPC channel is initialized or when AddFilter
+    // is called if the channel is already initialized.
+    virtual void OnFilterAdded(Channel* channel) {}
+
+    // Called on the background thread when the filter has been removed from
+    // the ChannelProxy and when the Channel is closing.  After a filter is
+    // removed, it will not be called again.
+    virtual void OnFilterRemoved() {}
+
+    // Called to inform the filter that the IPC channel is connected and we
+    // have received the internal Hello message from the peer.
+    virtual void OnChannelConnected(int32 peer_pid) {}
+
+    // Called when there is an error on the channel, typically that the channel
+    // has been closed.
+    virtual void OnChannelError() {}
+
+    // Called to inform the filter that the IPC channel will be destroyed.
+    // OnFilterRemoved is called immediately after this.
+    virtual void OnChannelClosing() {}
+
+    // Return true to indicate that the message was handled, or false to let
+    // the message be handled in the default way.
+    virtual bool OnMessageReceived(const Message& message) {
+      return false;
+    }
+  };
+
+  // Initializes a channel proxy.  The channel_id and mode parameters are
+  // passed directly to the underlying IPC::Channel.  The listener is called on
+  // the thread that creates the ChannelProxy.  The filter's OnMessageReceived
+  // method is called on the thread where the IPC::Channel is running.  The
+  // filter may be null if the consumer is not interested in handling messages
+  // on the background thread.  Any message not handled by the filter will be
+  // dispatched to the listener.  The given message loop indicates where the
+  // IPC::Channel should be created.
+  ChannelProxy(const std::string& channel_id, Channel::Mode mode,
+               Channel::Listener* listener, MessageFilter* filter,
+               MessageLoop* ipc_thread_loop);
+
+  ~ChannelProxy() {
+    Close();
+  }
+
+  // Close the IPC::Channel.  This operation completes asynchronously, once the
+  // background thread processes the command to close the channel.  It is ok to
+  // call this method multiple times.  Redundant calls are ignored.
+  //
+  // WARNING: The MessageFilter object held by the ChannelProxy is also
+  // released asynchronously, and it may in fact have its final reference
+  // released on the background thread.  The caller should be careful to deal
+  // with / allow for this possibility.
+  void Close();
+
+  // Send a message asynchronously.  The message is routed to the background
+  // thread where it is passed to the IPC::Channel's Send method.
+  virtual bool Send(Message* message);
+
+  // Used to intercept messages as they are received on the background thread.
+  //
+  // Ordinarily, messages sent to the ChannelProxy are routed to the matching
+  // listener on the worker thread.  This API allows code to intercept messages
+  // before they are sent to the worker thread.
+  void AddFilter(MessageFilter* filter);
+  void RemoveFilter(MessageFilter* filter);
+
+#if defined(OS_POSIX)
+  // Calls through to the underlying channel's methods.
+  // TODO(playmobil): For now this is only implemented in the case of
+  // create_pipe_now = true, we need to figure this out for the latter case.
+  int GetClientFileDescriptor() const;
+#endif  // defined(OS_POSIX)
+
+ protected:
+  class Context;
+  // A subclass uses this constructor if it needs to add more information
+  // to the internal state.  If create_pipe_now is true, the pipe is created
+  // immediately.  Otherwise it's created on the IO thread.
+  ChannelProxy(const std::string& channel_id, Channel::Mode mode,
+               MessageLoop* ipc_thread_loop, Context* context,
+               bool create_pipe_now);
+
+  // Used internally to hold state that is referenced on the IPC thread.
+  class Context : public base::RefCountedThreadSafe<Context>,
+                  public Channel::Listener {
+   public:
+    Context(Channel::Listener* listener, MessageFilter* filter,
+            MessageLoop* ipc_thread);
+    virtual ~Context() { }
+    MessageLoop* ipc_message_loop() const { return ipc_message_loop_; }
+    const std::string& channel_id() const { return channel_id_; }
+
+    // Dispatches a message on the listener thread.
+    void OnDispatchMessage(const Message& message);
+
+   protected:
+    // IPC::Channel::Listener methods:
+    virtual void OnMessageReceived(const Message& message);
+    virtual void OnChannelConnected(int32 peer_pid);
+    virtual void OnChannelError();
+
+    // Like OnMessageReceived but doesn't try the filters.
+    void OnMessageReceivedNoFilter(const Message& message);
+
+    // Gives the filters a chance at processing |message|.
+    // Returns true if the message was processed, false otherwise.
+    bool TryFilters(const Message& message);
+
+    // Like Open and Close, but called on the IPC thread.
+    virtual void OnChannelOpened();
+    virtual void OnChannelClosed();
+
+    // Called on the consumers thread when the ChannelProxy is closed.  At that
+    // point the consumer is telling us that they don't want to receive any
+    // more messages, so we honor that wish by forgetting them!
+    virtual void Clear() { listener_ = NULL; }
+
+   private:
+    friend class ChannelProxy;
+    // Create the Channel
+    void CreateChannel(const std::string& id, const Channel::Mode& mode);
+
+    // Methods called via InvokeLater:
+    void OnSendMessage(Message* message_ptr);
+    void OnAddFilter(MessageFilter* filter);
+    void OnRemoveFilter(MessageFilter* filter);
+    void OnDispatchConnected();
+    void OnDispatchError();
+
+    MessageLoop* listener_message_loop_;
+    Channel::Listener* listener_;
+
+    // List of filters.  This is only accessed on the IPC thread.
+    std::vector<scoped_refptr<MessageFilter> > filters_;
+    MessageLoop* ipc_message_loop_;
+    Channel* channel_;
+    std::string channel_id_;
+    int peer_pid_;
+    bool channel_connected_called_;
+  };
+
+  Context* context() { return context_; }
+
+ private:
+  void Init(const std::string& channel_id, Channel::Mode mode,
+            MessageLoop* ipc_thread_loop, bool create_pipe_now);
+
+  // By maintaining this indirection (ref-counted) to our internal state, we
+  // can safely be destroyed while the background thread continues to do stuff
+  // that involves this data.
+  scoped_refptr<Context> context_;
+};
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_CHANNEL_PROXY_H__