question: public void notifyThreadBusy ( final Thread thread ) { if ( thread == null ) { return ; } synchronized ( activationLock ) { synchronized ( mainLock ) { if ( blockerThread == null ) { activateBlockerThread ( ) ; } else if ( isReadyToShutdown ( ) ) { mainLock . notifyAll ( ) ; timeoutPassed = false ; } busyThreadSet . add ( thread ) ; } } }
target:  Add a specified thread to the set of busy event dispatch threads. If this set already contains the specified thread or the thread is null, the call leaves this set unchanged and returns silently.