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

ipc/ipc_sync_message.cc

-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// 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.
 
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
 #include <stack>
 
+#include "base/atomic_sequence_num.h"
 #include "base/logging.h"
 #include "base/waitable_event.h"
 #include "ipc/ipc_sync_message.h"
 
 namespace IPC {
 
-uint32 SyncMessage::next_id_ = 0;
 #define kSyncMessageHeaderSize 4
 
-base::WaitableEvent* dummy_event = new base::WaitableEvent(true, true);
+static base::AtomicSequenceNumber g_next_id(base::LINKER_INITIALIZED);
+
+static base::WaitableEvent* dummy_event = new base::WaitableEvent(true, true);
 
 SyncMessage::SyncMessage(
     int32 routing_id,
     uint32 type,
     PriorityValue priority,
     MessageReplyDeserializer* deserializer)
     : Message(routing_id, type, priority),
       deserializer_(deserializer),
       pump_messages_event_(NULL)
       {
   set_sync();
   set_unblock(true);
 
   // Add synchronous message data before the message payload.
   SyncHeader header;
-  header.message_id = ++next_id_;
+  header.message_id = g_next_id.GetNext();
   WriteSyncHeader(this, header);
 }
 
 MessageReplyDeserializer* SyncMessage::GetReplyDeserializer() {
   MessageReplyDeserializer* rv = deserializer_;
   DCHECK(rv);
   deserializer_ = NULL;
   return rv;
 }
 
@@ skipping 69 matching lines @@
 
   return true;
 }
 
 
 bool MessageReplyDeserializer::SerializeOutputParameters(const Message& msg) {
   return SerializeOutputParameters(msg, SyncMessage::GetDataIterator(&msg));
 }
 
 }  // namespace IPC