synchronizers: CountDownLatch vs CyclicBarrier vs Phaser vs Semaphore

One three-round worker pipeline implemented with CountDownLatch (one latch per round), CyclicBarrier (reusable, with a barrier action), and Phaser (reusable, plus dynamic mid-run registration), alongside Semaphore solving the genuinely different problem of bounding concurrent access. Covers timeout behavior (CyclicBarrier permanently breaks on one timeout, Phaser doesn't) and virtual-thread compatibility, including the corrected finding that Object.wait() releases its monitor and never pinned, unlike Thread.sleep() inside synchronized. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01FhzLY5p6okFva3qsnsRyvM
2026-09-30 06:43:52 +00:00
parent 0819993c51
commit 55ee850a75
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+$ java TimeoutBehaviorDemo
+
+=== CountDownLatch.await(timeout): expects 2, only 1 ever counts down ===
+await returned: false (false = timed out, latch still usable to re-check later)
+getCount() after timeout: 1
+
+=== CyclicBarrier.await(timeout): expects 2 parties, only 1 arrives ===
+await threw TimeoutException, as expected
+barrier.isBroken() after the timeout: true
+a second, later await() on the SAME barrier: BrokenBarrierException immediately - one timeout poisons the barrier for everyone until reset()
+
+=== Phaser.awaitAdvanceInterruptibly(phase, timeout): expects 2 parties, only 1 arrives ===
+awaitAdvanceInterruptibly threw TimeoutException, as expected
+phaser.getPhase() after the timeout: 0 (unchanged - still phase 0, not advanced or broken)
+a later round on the SAME phaser, once both parties actually arrive: succeeds normally, now at phase 1
+
+=== Semaphore.tryAcquire(timeout): 0 permits available ===
+tryAcquire returned: false (false = timed out, no exception, no broken state)
+a later tryAcquire after a release: true - fully independent of the earlier timeout
+done