Join threads after stopping.

src/marking-thread.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 55 matching lines @@
 
     end_marking_semaphore_->Signal();
   }
 }
 
 
 void MarkingThread::Stop() {
   Release_Store(&stop_thread_, static_cast<AtomicWord>(true));
   start_marking_semaphore_->Signal();
   stop_semaphore_->Wait();
+  Join();
 }
 
 
 void MarkingThread::StartMarking() {
   start_marking_semaphore_->Signal();
 }
 
 
 void MarkingThread::WaitForMarkingThread() {
   end_marking_semaphore_->Wait();
 }
 
 } }  // namespace v8::internal