private void wakeUp(){
  flushLock.lock();
  try {
    canFlush.signalAll();
  }
  finally {
    flushLock.unlock();
  }
}

private void wakeUp ( ) { flushLock . lock ( ) ; try { canFlush . signalAll ( ) ; } finally { flushLock . unlock ( ) ; } }
wakes up flushing threads if map size exceeded maximum value or in case of shutdown .
