Pepper proxy: make the browser sender handle the proxy lock properly.

ppapi/proxy/plugin_dispatcher.cc

 // Copyright (c) 2012 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 "ppapi/proxy/plugin_dispatcher.h"
 
 #include <map>
 
 #include "base/compiler_specific.h"
 #include "base/logging.h"
@@ skipping 174 matching lines @@
   // Allowing all async messages to unblock the renderer means more reentrancy
   // there but gives correct ordering.
   //
   // We don't want reply messages to unblock however, as they will potentially
   // end up on the wrong queue - see crbug.com/122443
   if (!msg->is_reply())
     msg->set_unblock(true);
   if (msg->is_sync()) {
     // Synchronous messages might be re-entrant, so we need to drop the lock.
     ProxyAutoUnlock unlock;
+
+    // TODO(yzshen): Make sending message thread-safe. It may be accessed from
+    // non-main threads. Moreover, since the proxy lock has been released, it
+    // may be accessed by multiple threads at the same time.

[brettw, 2012/11/27 00:49:15]

Is there a bug on this?

[yzshen1, 2012/11/30 04:29:13]

Yes. Although I haven't seen any bug reports, the Send() implementation doesn't
look safe. I will take a closer look and fix it.

     return Dispatcher::Send(msg);
   }
   return Dispatcher::Send(msg);
 }
 
 bool PluginDispatcher::OnMessageReceived(const IPC::Message& msg) {
   // We need to grab the proxy lock to ensure that we don't collide with the
   // plugin making pepper calls on a different thread.
   ProxyAutoLock lock;
   TRACE_EVENT2("ppapi proxy", "PluginDispatcher::OnMessageReceived",
@@ skipping 136 matching lines @@
   if (!resource) {
     if (reply_params.sequence())
       NOTREACHED();
     return;
   }
   resource->OnReplyReceived(reply_params, nested_msg);
 }
 
 }  // namespace proxy
 }  // namespace ppapi