1. 6.5 AbstractQueuedSynchronizer (AQS)historical

    AQS as the state-and-wait-queue framework behind many JUC synchronizers, with exclusive/shared acquisition, parking, cancellation, and template methods.

  2. Building an AQS-Style Synchronizerhistorical

    A teaching implementation of a synchronizer using atomic state, a FIFO wait queue, park/unpark, and release wakeups, emphasizing invariants rather than copying JDK internals.