Allow synchronous messages to be sent from threads other than the main thread...

ipc/ipc_sync_message_filter.h

+// Copyright (c) 2010 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_SYNC_MESSAGE_FILTER_H_
+#define IPC_IPC_SYNC_MESSAGE_FILTER_H_
+
+#include "base/basictypes.h"
+#include "base/hash_tables.h"
+#include "base/lock.h"
+#include "base/ref_counted.h"
+#include "base/waitable_event.h"
+#include "ipc/ipc_channel_proxy.h"
+#include "ipc/ipc_sync_message.h"
+
+class MessageLoop;
+
+#if defined(COMPILER_GCC)
+// Allows us to use MessageLoop in a hash_map with gcc (MSVC is okay without
+// specifying this).
+namespace __gnu_cxx {
+template<>
+struct hash<MessageLoop*> {
+  size_t operator()(MessageLoop* message_loop) const {
+    return reinterpret_cast<size_t>(message_loop);
+  }
+};
+}
+#endif
+
+namespace IPC {
+
+class MessageReplyDeserializer;
+
+// This MessageFilter allows sending synchronous IPC messages from a thread
+// other than the listener thread associated with the SyncChannel.  It does not
+// support fancy features that SyncChannel does, such as handling recursion or
+// receiving messages while waiting for a response.  Note that this object can
+// be used to send simultaneous synchronous messages from different threads.
+class SyncMessageFilter : public ChannelProxy::MessageFilter,
+                          public Message::Sender {
+ public:
+  explicit SyncMessageFilter(base::WaitableEvent* shutdown_event);
+  virtual ~SyncMessageFilter();
+
+  // Message::Sender implementation.
+  virtual bool Send(Message* message);
+
+  // ChannelProxy::MessageFilter implementation.
+  virtual void OnFilterAdded(Channel* channel);
+  virtual void OnChannelError();
+  virtual void OnChannelClosing();
+  virtual bool OnMessageReceived(const Message& message);
+
+ private:
+  void SendOnIOThread(Message* message);
+  // Signal all the pending sends as done, used in an error condition.
+  void SignalAllEvents();
+
+  // The channel to which this filter was added.
+  Channel* channel_;
+
+  MessageLoop* listener_loop_;  // The process's main thread.
+  MessageLoop* io_loop_;  // The message loop where the Channel lives.
+
+  typedef base::hash_map<MessageLoop*, PendingSyncMsg*> PendingSyncMessages;
+  PendingSyncMessages pending_sync_messages_;
+
+  // Locks data members above.
+  Lock lock_;
+
+  base::WaitableEvent* shutdown_event_;
+
+  DISALLOW_COPY_AND_ASSIGN(SyncMessageFilter);
+};
+
+}  // namespace IPC
+
+#endif  // IPC_IPC_SYNC_MESSAGE_FILTER_H_