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synchronizers: CountDownLatch vs CyclicBarrier vs Phaser vs Semaphore

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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
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asmhatre
2026-09-30 06:43:52 +00:00
co-authored by Claude Sonnet 5
parent 0819993c51
commit 55ee850a75
20 changed files with 962 additions and 0 deletions
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synchronizers/output/06-virtual-thread-compatibility.txt
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$ java -Djdk.tracePinnedThreads=full VirtualThreadCompatibilityDemo (pre-JDK-24 runtime)
java.version=21.0.10
jdk.tracePinnedThreads=full
CountDownLatch.await(): completed, no trace above this line for it
CyclicBarrier.await(): completed, no trace above this line for it
Phaser.arriveAndAwaitAdvance(): completed, no trace above this line for it
Semaphore.acquire(): completed, no trace above this line for it
done - no pinning trace printed above for any of the four
$ java -Djdk.tracePinnedThreads=full SynchronizedWaitPinsDemo (pre-JDK-24 runtime, contrast case)
java.version=21.0.10
jdk.tracePinnedThreads=full
synchronized + Object.wait(): completed, no pinning trace above this line for it
VirtualThread[#21]/runnable@ForkJoinPool-1-worker-1 reason:MONITOR
java.base/java.lang.VirtualThread$VThreadContinuation.onPinned(VirtualThread.java:199)
java.base/jdk.internal.vm.Continuation.onPinned0(Continuation.java:393)
java.base/java.lang.VirtualThread.parkNanos(VirtualThread.java:635)
java.base/java.lang.VirtualThread.sleepNanos(VirtualThread.java:807)
java.base/java.lang.Thread.sleep(Thread.java:507)
com.ankurm.synchronizers.SynchronizedWaitPinsDemo.lambda$main$1(SynchronizedWaitPinsDemo.java:48) <== monitors:1
java.base/java.lang.VirtualThread.run(VirtualThread.java:329)
synchronized + Thread.sleep(): completed, pinning trace (if any) appears above this line for it
done