Why does the acquire() method in Semaphores not have to be synchronized?

Question

I am getting into Semaphores in Java and was reading this article http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/Semaphore.html . The only thing I don\'t

Answer 1

synchronization is guaranteed by AbstractQueuedSynchronizer with CAS operations

see the javadoc here