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
20 changed files with 962 additions and 0 deletions
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+#!/usr/bin/env bash
+# Regenerates every file in output/. Requires:
+#   - JDK25_HOME pointing at a JDK 24+ install (this repo used Temurin 25.0.4.1+1)
+#   - JDK21_HOME pointing at a pre-JDK-24 install (this repo used OpenJDK 21.0.10), for the
+#     virtual-thread pinning contrast at the end
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+: "${JDK25_HOME:?Set JDK25_HOME to a JDK 24+ install}"
+: "${JDK21_HOME:?Set JDK21_HOME to a pre-JDK-24 install}"
+
+mkdir -p target/classes target/classes-21
+"$JDK25_HOME/bin/javac" --release 25 -d target/classes $(find src/main/java -name "*.java")
+"$JDK21_HOME/bin/javac" --release 21 -d target/classes-21 $(find src/main/java -name "*.java")
+
+echo "--- 01: CountDownLatch pipeline ---"
+{
+  echo '$ java CountDownLatchPipeline'
+  echo ""
+  "$JDK25_HOME/bin/java" -cp target/classes com.ankurm.synchronizers.CountDownLatchPipeline 2>&1 | grep -v "Picked up"
+} > output/01-countdownlatch-pipeline.txt
+
+echo "--- 02: CyclicBarrier pipeline ---"
+{
+  echo '$ java CyclicBarrierPipeline'
+  echo ""
+  "$JDK25_HOME/bin/java" -cp target/classes com.ankurm.synchronizers.CyclicBarrierPipeline 2>&1 | grep -v "Picked up"
+} > output/02-cyclicbarrier-pipeline.txt
+
+echo "--- 03: Phaser pipeline (dynamic registration) ---"
+{
+  echo '$ java PhaserPipeline'
+  echo ""
+  "$JDK25_HOME/bin/java" -cp target/classes com.ankurm.synchronizers.PhaserPipeline 2>&1 | grep -v "Picked up"
+} > output/03-phaser-pipeline.txt
+
+echo "--- 04: Semaphore resource guard ---"
+{
+  echo '$ java SemaphoreResourceGuard'
+  echo ""
+  "$JDK25_HOME/bin/java" -cp target/classes com.ankurm.synchronizers.SemaphoreResourceGuard 2>&1 | grep -v "Picked up"
+} > output/04-semaphore-resource-guard.txt
+
+echo "--- 05: timeout behavior across all four ---"
+{
+  echo '$ java TimeoutBehaviorDemo'
+  echo ""
+  "$JDK25_HOME/bin/java" -cp target/classes com.ankurm.synchronizers.TimeoutBehaviorDemo 2>&1 | grep -v "Picked up"
+} > output/05-timeout-behavior.txt
+
+echo "--- 06: virtual-thread compatibility, all four, on JDK21 (pre-JEP-491) ---"
+{
+  echo '$ java -Djdk.tracePinnedThreads=full VirtualThreadCompatibilityDemo   (pre-JDK-24 runtime)'
+  echo ""
+  "$JDK21_HOME/bin/java" -Djdk.tracePinnedThreads=full -cp target/classes-21 \
+    com.ankurm.synchronizers.VirtualThreadCompatibilityDemo 2>&1 | grep -v "Picked up"
+  echo ""
+  echo '$ java -Djdk.tracePinnedThreads=full SynchronizedWaitPinsDemo   (pre-JDK-24 runtime, contrast case)'
+  echo ""
+  "$JDK21_HOME/bin/java" -Djdk.tracePinnedThreads=full -cp target/classes-21 \
+    com.ankurm.synchronizers.SynchronizedWaitPinsDemo 2>&1 | grep -v "Picked up"
+} > output/06-virtual-thread-compatibility.txt
+
+echo "--- 07: correctness tests ---"
+"$JDK25_HOME/bin/java" --version > /dev/null # sanity
+(cd "$(pwd)" && JAVA_HOME="$JDK25_HOME" mvn -q -f pom.xml test 2>&1 | grep -v "Picked up\|WARNING" || true)
+cp target/surefire-reports/com.ankurm.synchronizers.RoundOrderingCorrectnessTest.txt output/07-round-ordering-correctness.txt
+
+echo "Done. See output/."