AQS in Java.util.concurrent Synchronizer Classes

Summary

If you need to implement a state-dependent classone whose methods must block if a state-based precondition does not holdthe best strategy is usually to build upon an existing library class such as Semaphore, BlockingQueue, or CountDownLatch, as in ValueLatch on page 187. However, sometimes existing library classes do not provide a sufficient foundation; in these cases, you can build your own synchronizers using intrinsic condition queues, explicit Condition objects, or AbstractQueuedSynchronizer. Intrinsic condition queues are tightly bound to intrinsic locking, since the mechanism for managing state dependence is necessarily tied to the mechanism for ensuring state consistency. Similarly, explicit Conditions are tightly bound to explicit Locks, and offer an extended feature set compared to intrinsic condition queues, including multiple wait sets per lock, interruptible or uninterruptible condition waits, fair or nonfair queuing, and deadline-based waiting.