question: private byte [ ] firstElement ( ) throws KeeperException , InterruptedException { while ( true ) { String firstChild = firstChild ( false ) ; if ( firstChild == null ) { return null ; } try { return zookeeper . getData ( dir + "/" + firstChild , null , null , true ) ; } catch ( KeeperException . NoNodeException e ) { updateLock . lockInterruptibly ( ) ; try { knownChildren . remove ( firstChild ) ; } finally { updateLock . unlock ( ) ; } } } }
target:  Return the head of the queue without modifying the queue.