Add multithreading module: odd-even, ping-pong, ordered threads, deadlock detection and fixes, virtual-thread variants (25 tests)

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b7rnC7jppGGdHGESvy

multithreading/output/01-odd-even.txt

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+OddEvenWaitNotify (platform threads), max=10
+  [odd:1, even:2, odd:3, even:4, odd:5, even:6, odd:7, even:8, odd:9, even:10]
+OddEvenSemaphore (platform threads), max=10
+  [odd:1, even:2, odd:3, even:4, odd:5, even:6, odd:7, even:8, odd:9, even:10]
+OddEvenLockCondition (platform threads), max=10
+  [odd:1, even:2, odd:3, even:4, odd:5, even:6, odd:7, even:8, odd:9, even:10]

multithreading/output/02-ping-pong.txt

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+PingPong, 4 rounds
+  [ping, pong, ping, pong, ping, pong, ping, pong]

multithreading/output/03-ordered-threads.txt

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+Started T3, T2, T1 (in that order). Execution order:
+  latches:     [T1, T2, T3]
+  join chain:  [T1, T2, T3]
+Round robin, 3 threads, max=10:
+  [worker-1:1, worker-2:2, worker-3:3, worker-1:4, worker-2:5, worker-3:6, worker-1:7, worker-2:8, worker-3:9, worker-1:10]

multithreading/output/04-deadlock.txt

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+== NAIVE ==
+  findDeadlockedThreads: DEADLOCK
+    transfer-A-to-B is WAITING on java.util.concurrent.locks.ReentrantLock$NonfairSync owned by transfer-B-to-A
+    transfer-B-to-A is WAITING on java.util.concurrent.locks.ReentrantLock$NonfairSync owned by transfer-A-to-B
+  after interrupting both threads: total balance = 2000
+== ORDERED ==
+  both transfers completed, no deadlock to detect
+  balances A=930 B=1070
+== TRY_LOCK ==
+  both transfers completed, no deadlock to detect
+  balances A=930 B=1070 retries>0=true
+== NAIVE on virtual threads ==
+  thread states: [WAITING, WAITING]
+  findDeadlockedThreads: none (virtual threads are invisible to it)

multithreading/output/05-virtual-single-carrier.txt

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+carrier parallelism = 1
+OddEvenWaitNotify on virtual threads, max=10
+  [odd:1, even:2, odd:3, even:4, odd:5, even:6, odd:7, even:8, odd:9, even:10]
+Round robin: 1000 virtual threads, max=3000 -> 3000 events
+  first 3: [worker-1:1, worker-2:2, worker-3:3]
+  last 3:  [worker-998:2998, worker-999:2999, worker-1000:3000]

multithreading/output/06-test-results.txt

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+PASS DeadlockTest.naiveLockingDeadlocksAndTheJvmSaysSo
+PASS DeadlockTest.consistentLockOrderingRemovesTheCycle
+PASS DeadlockTest.fixesAlsoWorkOnVirtualThreads
+PASS DeadlockTest.tryLockWithBackOffTurnsDeadlockIntoCountedRetries
+PASS DeadlockTest.deadlockedVirtualThreadsAreInvisibleToFindDeadlockedThreads
+PASS OddEvenTest.everyImplementationPrintsExactlyOneToTwentyInOrder(ThreadKind)[1]
+PASS OddEvenTest.everyImplementationPrintsExactlyOneToTwentyInOrder(ThreadKind)[2]
+PASS OddEvenTest.twoDifferentThreadsDoTheWork(ThreadKind)[1]
+PASS OddEvenTest.twoDifferentThreadsDoTheWork(ThreadKind)[2]
+PASS OddEvenTest.stableAcrossManyRunsAndOddMax(ThreadKind)[1]
+PASS OddEvenTest.stableAcrossManyRunsAndOddMax(ThreadKind)[2]
+PASS OddEvenTest.zeroAndOneAreHandled(ThreadKind)[1]
+PASS OddEvenTest.zeroAndOneAreHandled(ThreadKind)[2]
+PASS OrderedThreadsTest.roundRobinOfThreeThreadsPrintsOneToTen(ThreadKind)[1]
+PASS OrderedThreadsTest.roundRobinOfThreeThreadsPrintsOneToTen(ThreadKind)[2]
+PASS OrderedThreadsTest.latchesRunT1T2T3EvenThoughT3StartsFirst(ThreadKind)[1]
+PASS OrderedThreadsTest.latchesRunT1T2T3EvenThoughT3StartsFirst(ThreadKind)[2]
+PASS OrderedThreadsTest.thousandVirtualThreadsStillPrintInOrder
+PASS OrderedThreadsTest.joinChainRunsT1T2T3(ThreadKind)[1]
+PASS OrderedThreadsTest.joinChainRunsT1T2T3(ThreadKind)[2]
+PASS PingPongTest.zeroRoundsPrintNothing(ThreadKind)[1]
+PASS PingPongTest.zeroRoundsPrintNothing(ThreadKind)[2]
+PASS PingPongTest.alternatesStrictlyForGivenRounds(ThreadKind)[1]
+PASS PingPongTest.alternatesStrictlyForGivenRounds(ThreadKind)[2]
+PASS SingleCarrierVirtualThreadTest.waitNotifyFinishesOnOneCarrierThread
+25 tests, 0 failures