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
2026-09-30 07:25:12 +00:00
parent bc5153d2a5
commit 202f2f18a5
15 changed files with 553 additions and 0 deletions
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+=== Same-thread binding: visible to direct AND indirect callees ===
+handleRequest(): REQUEST_ID.get() = req-42
+logSomewhereDeeper() (indirect callee, same thread): REQUEST_ID.get() = req-42
+
+=== Outside any binding: isBound() is false ===
+main: REQUEST_ID.isBound() = false
+
+=== A plain `new Thread()` does NOT inherit the binding ===
+plain child thread: REQUEST_ID.isBound() = false
+
+=== A StructuredTaskScope.fork()'d thread DOES inherit the binding ===
+forked subtask: REQUEST_ID.isBound() = true, REQUEST_ID.get() = req-100
+done