jmm: Java Memory Model companion code (volatile, happens-before, DCL)

Runnable jcstress + JUnit companion for the ankurm.com post on the Java Memory Model, double-checked locking, and the volatile fix.
2026-09-30 05:31:29 +00:00
commit f548d9eeb5
22 changed files with 721 additions and 0 deletions
@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Regenerates every file in output/. Run from the jmm/ directory after `mvn package`.
+#
+# Needs a JDK 25 on PATH (or set JAVA_HOME below) - jcstress-core 0.16's annotation
+# processor is NOT auto-discovered by javac on JDK 25 without -processorpath, which is
+# why the pom's <annotationProcessorPaths> block exists; see output/04-*.txt.
+#
+# The three jcstress runs below use a fixed, non-default JVM config (-jvmArgs) on
+# purpose: without it, jcstress auto-detects and iterates over several compiler-flag
+# combinations, multiplying the number of forked JVMs far past what this sandbox's
+# 2 CPUs can get through in a reasonable time. -f 2 -iters 15 -time 1000 with a fixed
+# JVM config took about 4m45s per test on that hardware.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+JAR=target/jcstress.jar
+[ -f "$JAR" ] || { echo "Run 'mvn package' first."; exit 1; }
+
+run_test() {
+  local test_class="$1" out_file="$2"
+  echo "==> $test_class"
+  {
+    echo "\$ java -jar target/jcstress.jar -t $test_class -jvmArgs \"-Xmx256m\" -f 2 -iters 15 -time 1000"
+    echo
+  } > "$out_file"
+  java -jar "$JAR" -t "$test_class" -jvmArgs "-Xmx256m" -f 2 -iters 15 -time 1000 -v 2>/dev/null \
+    | awk '/^RUN RESULTS:/{p=1} p==1 && /VM error stream:/{exit} p' >> "$out_file"
+}
+
+run_test PlainPublicationTest      output/01-plain-publication.txt
+run_test VolatilePublicationTest   output/02-volatile-publication.txt
+run_test FinalFieldPublicationTest output/03-final-field-publication.txt
+
+echo "==> SingletonBehaviorTest (JUnit)"
+mvn -q test
+{
+  echo '$ mvn -q test'
+  echo
+  cat target/surefire-reports/com.ankurm.jmm.SingletonBehaviorTest.txt
+} > output/05-singleton-behavior.txt
+
+echo "Done. output/ regenerated."
@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+# Quick ad hoc jcstress run against one test class, printed to the terminal instead of
+# a captured output/ file. Example:
+#   ./scripts/run.sh PlainPublicationTest
+#   ./scripts/run.sh PlainPublicationTest -m tough      # extra args pass straight through
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+TEST="${1:?Usage: run.sh <TestClassName> [extra jcstress args]}"
+shift || true
+
+JAR=target/jcstress.jar
+[ -f "$JAR" ] || { echo "Run 'mvn package' first."; exit 1; }
+
+java -jar "$JAR" -t "$TEST" -jvmArgs "-Xmx256m" -f 2 -iters 15 -time 1000 -v "$@"