question: public static < T > long addAndGet ( AtomicLongFieldUpdater < T > updater , T instance , long n ) { for ( ; ; ) { long r = updater . get ( instance ) ; if ( r == Long . MAX_VALUE ) { return Long . MAX_VALUE ; } long u = addCap ( r , n ) ; if ( updater . compareAndSet ( instance , r , u ) ) { return r ; } } }
target:  Concurrent addition bound to Long.MAX_VALUE. Any concurrent write will "happen" before this operation.