concurrency-interview: companion code for the Top 40 interview post

Adds the concurrency-interview module: a real race condition with its
actual lost-update count, why volatile alone doesn't fix it, a real
JVM-detected deadlock (ThreadMXBean.findDeadlockedThreads()) with the
fix, and ScopedValue's exact child-thread inheritance rules (finalized
in JDK 25 via JEP 506, demonstrated against StructuredTaskScope, still
preview per JEP 505/525). 4 runnable demos, 1 JUnit test class (9
tests), 5 captured output transcripts.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01FhzLY5p6okFva3qsnsRyvM

concurrency-interview/scripts/run-all.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Regenerates every file in ../output/. Requires JDK25_HOME. Every demo in this module needs
+# --enable-preview to run (ScopedValueDemo uses StructuredTaskScope, still preview in JDK 25/26),
+# even though ScopedValue itself is finalized (JEP 506).
+set -euo pipefail
+
+if [[ -z "${JDK25_HOME:-}" ]]; then
+  echo "JDK25_HOME must be set (e.g. /path/to/jdk-25)" >&2
+  exit 1
+fi
+
+cd "$(dirname "$0")/.."
+OUT=output
+mkdir -p "$OUT"
+
+JAVA_HOME="$JDK25_HOME" mvn -q -f ../pom.xml -pl concurrency-interview package
+
+run() {
+  local class=$1
+  local outfile=$2
+  echo "==> $class"
+  "$JDK25_HOME/bin/java" --enable-preview -cp target/classes "com.ankurm.concurrencyinterview.$class" 2>&1 | grep -v "Picked up" > "$OUT/$outfile"
+}
+
+run RaceConditionDemo         01-race-condition.txt
+run VolatileNotEnoughDemo     02-volatile-not-enough.txt
+run DeadlockDemo              03-deadlock-detection.txt
+run ScopedValueDemo           04-scoped-value-inheritance.txt
+
+cp target/surefire-reports/com.ankurm.concurrencyinterview.InterviewClaimsTest.txt "$OUT/05-correctness-tests.txt"
+
+echo "Done. See $OUT/"