Join threads after stopping.

src/sweeper-thread.cc

 // Copyright 2012 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 75 matching lines @@
     return space->free_list()->Concatenate(&free_list_old_data_space_);
   }
   return 0;
 }
 
 
 void SweeperThread::Stop() {
   Release_Store(&stop_thread_, static_cast<AtomicWord>(true));
   start_sweeping_semaphore_->Signal();
   stop_semaphore_->Wait();
+  Join();
 }
 
 
 void SweeperThread::StartSweeping() {
   start_sweeping_semaphore_->Signal();
 }
 
 
 void SweeperThread::WaitForSweeperThread() {
   end_sweeping_semaphore_->Wait();
 }
 } }  // namespace v8::internal