Prevent data race in MessageQueue.

webrtc/base/thread.cc

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 335 matching lines @@
   {
     CritScope cs(&crit_);
     _SendMessage smsg;
     smsg.thread = current_thread;
     smsg.msg = msg;
     smsg.ready = &ready;
     sendlist_.push_back(smsg);
   }
 
   // Wait for a reply
-
-  ss_->WakeUp();
+  {
+    SharedScope ss(&ss_lock_);
+    ss_->WakeUp();

[pthatcher1, 2016/02/12 00:16:33]

Instead of making ss_lock_ protected, could we just call
socketserver()->WakeUp() here?

[joachim, 2016/02/12 15:09:52]

That would still be racy imho because the variable would not be locked between
the return of the socketserver() and the invokation of "WakeUp". Instead I
introduced a method "WakeUpSocketServer()" in MessageQueue that takes care of
proper locking.

With that, the socket server related properties can be made private in
MessageQueue.

+  }
 
   bool waited = false;
   crit_.Enter();
   while (!ready) {
     crit_.Leave();
     // We need to limit "ReceiveSends" to |this| thread to avoid an arbitrary
     // thread invoking calls on the current thread.
     current_thread->ReceiveSendsFromThread(this);
     current_thread->socketserver()->Wait(kForever, false);
     waited = true;
@@ skipping 166 matching lines @@
   if (SUCCEEDED(hr)) {
     Thread::Run();
     CoUninitialize();
   } else {
     LOG(LS_ERROR) << "CoInitialize failed, hr=" << hr;
   }
 }
 #endif
 
 }  // namespace rtc