Ensure that |Thread::id_| is only accessed when an happens-after relationship has been established …

base/threading/thread.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 "base/threading/thread.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/lazy_instance.h"
 #include "base/location.h"
@@ skipping 205 matching lines @@
   if (message_loop_ && !stopping_)
     return true;
   // Otherwise check the |running_| flag, which is set to true by the new thread
   // only while it is inside Run().
   AutoLock lock(running_lock_);
   return running_;
 }
 
 void Thread::Run(RunLoop* run_loop) {
   // Overridable protected method to be called from our |thread_| only.
+  DCHECK(id_event_.IsSignaled());
   DCHECK_EQ(id_, PlatformThread::CurrentId());
 
   run_loop->Run();
 }
 
 // static
 void Thread::SetThreadWasQuitProperly(bool flag) {
   lazy_tls_bool.Pointer()->Set(flag);
 }
 
@@ skipping 20 matching lines @@
   DCHECK(!IsRunning());
   message_loop_ = message_loop;
   DCHECK(IsRunning());
 
   using_external_message_loop_ = true;
 }
 
 void Thread::ThreadMain() {
   // First, make GetThreadId() available to avoid deadlocks. It could be called
   // any place in the following thread initialization code.
+  DCHECK(!id_event_.IsSignaled());
+  // Note: this read of |id_| while |id_event_| isn't signaled is exceptionally
+  // okay because ThreadMain has an happens-after relationship with the other
+  // write in StartWithOptions().
+  DCHECK_EQ(kInvalidThreadId, id_);
   id_ = PlatformThread::CurrentId();
   DCHECK_NE(kInvalidThreadId, id_);
   id_event_.Signal();
 
   // Complete the initialization of our Thread object.
   PlatformThread::SetName(name_.c_str());
   ANNOTATE_THREAD_NAME(name_.c_str());  // Tell the name to race detector.
 
   // Lazily initialize the |message_loop| so that it can run on this thread.
   DCHECK(message_loop_);
@@ skipping 49 matching lines @@
   run_loop_ = nullptr;
 }
 
 void Thread::ThreadQuitHelper() {
   DCHECK(run_loop_);
   run_loop_->QuitWhenIdle();
   SetThreadWasQuitProperly(true);
 }
 
 }  // namespace base