public void shutdown(){
  while (true) {
    long cur=combinedState.get();
    long newValue=cur | 0x8000000000000000L;
    if (combinedState.compareAndSet(cur,newValue)) {
      break;
    }
  }
}

public void shutdown ( ) { while ( true ) { long cur = combinedState . get ( ) ; long newValue = cur | 0x8000000000000000L ; if ( combinedState . compareAndSet ( cur , newValue ) ) { break ; } } }
initiates an orderly shutdown in which previously submitted tasks are executed , but no new tasks will be accepted . invocation has no additional effect if already shut down .
