vt-pinning: diagnosing virtual thread pinning companion code
Reproduces the pinning JEP 491 did not fix (native JNI frames) with a real native library, alongside the monitor case it did fix. Covers the jdk.VirtualThreadPinned JFR event, reading pinned vs unmounted virtual threads from a jcmd Thread.dump_to_file, the measured throughput cost on a capped carrier pool, and a bounded-executor pattern to contain the blast radius. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01FhzLY5p6okFva3qsnsRyvM
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Claude Sonnet 5
Executable
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#!/usr/bin/env bash
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# Regenerates every file in output/. Requires:
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# - JDK25_HOME pointing at a JDK 24+ install (this repo used Temurin 25.0.4.1+1)
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# - JDK21_HOME pointing at a pre-JDK-24 install (this repo used OpenJDK 21.0.10), for the
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# before/after comparisons against JEP 491
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# - gcc on PATH (builds the JNI native library)
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set -euo pipefail
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cd "$(dirname "$0")/.."
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: "${JDK25_HOME:?Set JDK25_HOME to a JDK 24+ install}"
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: "${JDK21_HOME:?Set JDK21_HOME to a pre-JDK-24 install}"
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JAVA_HOME="$JDK21_HOME" ./scripts/build-native.sh
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mkdir -p target/classes target/classes-21
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"$JDK25_HOME/bin/javac" --release 25 -d target/classes $(find src/main/java -name "*.java")
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"$JDK21_HOME/bin/javac" --release 21 -d target/classes-21 $(find src/main/java -name "*.java")
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NATLIB=target/native
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echo "--- 01: monitor pinning, JDK21 vs JDK25 (JEP 491) ---"
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{
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echo '$ java -Djdk.tracePinnedThreads=full MonitorPinningDemo (pre-JDK-24 runtime)'
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echo ""
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"$JDK21_HOME/bin/java" -Djdk.tracePinnedThreads=full -cp target/classes-21 \
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com.ankurm.vtpinning.MonitorPinningDemo 2>&1 | grep -v "Picked up"
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echo ""
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echo '$ java -Djdk.tracePinnedThreads=full MonitorPinningDemo (JDK 24+ runtime)'
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echo ""
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"$JDK25_HOME/bin/java" -Djdk.tracePinnedThreads=full -cp target/classes \
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com.ankurm.vtpinning.MonitorPinningDemo 2>&1 | grep -v "Picked up"
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} > output/01-monitor-pinning-jdk21-vs-jdk25.txt
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echo "--- 02: native pinning, JDK21 vs JDK25 (still real on both) ---"
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{
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echo '$ java -Djdk.tracePinnedThreads=full NativePinningDemo (pre-JDK-24 runtime)'
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echo ""
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"$JDK21_HOME/bin/java" -Djdk.tracePinnedThreads=full -Djava.library.path=$NATLIB -cp target/classes-21 \
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com.ankurm.vtpinning.NativePinningDemo 2>&1 | grep -v "Picked up"
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echo ""
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echo '$ java -Djdk.tracePinnedThreads=full NativePinningDemo (JDK 24+ runtime - flag is inert)'
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echo ""
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED -Djdk.tracePinnedThreads=full -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.NativePinningDemo 2>&1 | grep -v "Picked up\|WARNING"
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} > output/02-native-pinning-jdk21-vs-jdk25.txt
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echo "--- 03: jdk.VirtualThreadPinned JFR event on JDK25 ---"
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rm -f target/native-pin.jfr
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{
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echo '$ java -XX:StartFlightRecording=...,jdk.VirtualThreadPinned#enabled=true,threshold=0ms NativePinningDemo'
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echo ""
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED \
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"-XX:StartFlightRecording=filename=target/native-pin.jfr,settings=profile,jdk.VirtualThreadPinned#enabled=true,jdk.VirtualThreadPinned#threshold=0ms,jdk.VirtualThreadPinned#stackTrace=true" \
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-Djava.library.path=$NATLIB -cp target/classes com.ankurm.vtpinning.NativePinningDemo 2>&1 \
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| grep -v "Picked up\|WARNING\|jfr,startup\|^\["
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echo ""
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echo '$ jfr print --events jdk.VirtualThreadPinned --stack-depth 10 target/native-pin.jfr'
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echo ""
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"$JDK25_HOME/bin/jfr" print --events jdk.VirtualThreadPinned --stack-depth 10 target/native-pin.jfr 2>&1 | grep -v "Picked up"
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} > output/03-jfr-virtualthreadpinned-event.txt
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echo "--- 04: jcmd Thread.dump_to_file, pinned vs unpinned virtual thread ---"
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rm -f target/threaddump.json target/threaddump_out.txt
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.ThreadDumpPinnedDemo > target/threaddump_out.txt 2>&1 &
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PID=$!
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sleep 1.5
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"$JDK25_HOME/bin/jcmd" "$PID" Thread.dump_to_file -format=json target/threaddump.json > target/jcmd_out.txt 2>&1
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wait $PID
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{
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echo '$ java ThreadDumpPinnedDemo &'
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grep -v "Picked up" target/threaddump_out.txt
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echo ""
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echo '$ jcmd <pid> Thread.dump_to_file -format=json threaddump.json (taken mid-flight)'
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grep -v "Picked up" target/jcmd_out.txt
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echo ""
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echo '--- the two virtual thread entries from that dump ---'
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python3 - <<'PYEOF'
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import json
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with open('target/threaddump.json') as f:
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data = json.load(f)
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for c in data['threadDump']['threadContainers']:
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for t in c.get('threads', []):
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if t.get('virtual'):
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print(json.dumps(t, indent=2))
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print()
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PYEOF
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} > output/04-jcmd-thread-dump-pinned-vs-unpinned.txt
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echo "--- 05: throughput cost of native pinning vs plain blocking (capped carriers) ---"
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{
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echo '$ java -Djdk.virtualThreadScheduler.parallelism=2 PinningThroughputDemo native 4 1000'
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED -Djdk.virtualThreadScheduler.parallelism=2 -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.PinningThroughputDemo native 4 1000 2>&1 | grep -v "Picked up\|WARNING"
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echo ""
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echo '$ java -Djdk.virtualThreadScheduler.parallelism=2 PinningThroughputDemo plain 4 1000'
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"$JDK25_HOME/bin/java" -Djdk.virtualThreadScheduler.parallelism=2 -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.PinningThroughputDemo plain 4 1000 2>&1 | grep -v "Picked up\|WARNING"
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} > output/05-pinning-throughput-cost.txt
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echo "--- 06: bounding the blast radius with a dedicated executor ---"
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{
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echo '$ java -Djdk.virtualThreadScheduler.parallelism=2 BoundedNativeCallDemo direct'
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED -Djdk.virtualThreadScheduler.parallelism=2 -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.BoundedNativeCallDemo direct 2>&1 | grep -v "Picked up\|WARNING"
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echo ""
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echo '$ java -Djdk.virtualThreadScheduler.parallelism=2 BoundedNativeCallDemo bounded'
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"$JDK25_HOME/bin/java" --enable-native-access=ALL-UNNAMED -Djdk.virtualThreadScheduler.parallelism=2 -Djava.library.path=$NATLIB -cp target/classes \
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com.ankurm.vtpinning.BoundedNativeCallDemo bounded 2>&1 | grep -v "Picked up\|WARNING"
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} > output/06-bounded-executor-fix.txt
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echo "Done. See output/."
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