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December 3, 2025 21:21
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| private static final ScopedValue<ExecutionContext> EXECUTION_CTX = ScopedValue.newInstance(); | |
| private static final class ExecutionContext { | |
| private final ReentrantLock lock = new ReentrantLock(true); | |
| private final AtomicReference<CountDownLatch> suspended = new AtomicReference<>(null); | |
| /** | |
| * This can be called by any thread! | |
| */ | |
| public void resume() { | |
| var toResume = suspended.getAndSet(null); | |
| if (toResume != null) { | |
| toResume.countDown(); | |
| } | |
| } | |
| public boolean isSuspended() { | |
| return suspended.get() != null; | |
| } | |
| void suspend() { | |
| var ctx = EXECUTION_CTX.orElseThrow(IllegalStateException::new); | |
| if (ctx != this) { | |
| throw new IllegalStateException("Wrong execution context"); | |
| } | |
| assert lock.isHeldByCurrentThread(); | |
| var latch = new CountDownLatch(1); | |
| suspended.lazySet(latch); | |
| try { | |
| latch.await(); | |
| } catch (Throwable _) { | |
| } | |
| } | |
| private void runSerialized(Runnable task) { | |
| lock.lock(); | |
| try { | |
| task.run(); | |
| } finally { | |
| lock.unlock(); | |
| } | |
| } | |
| } | |
| @Test | |
| void testSerializeExecution() throws Exception { | |
| List<Integer> sequence = Collections.synchronizedList(new ArrayList<>()); | |
| try (var group = new VirtualMultithreadIoEventLoopGroup(1, LocalIoHandler.newFactory())) { | |
| var eventLoopFactory = group.vThreadFactory(); | |
| var sharedExecutionCtx = new ExecutionContext(); | |
| ThreadFactory serializerFactory = task -> eventLoopFactory.newThread(() -> ScopedValue | |
| .where(EXECUTION_CTX, sharedExecutionCtx).run(() -> sharedExecutionCtx.runSerialized(task))); | |
| serializerFactory.newThread(() -> { | |
| var ctx = EXECUTION_CTX.get(); | |
| Thread.startVirtualThread(() -> { | |
| // make sure that the context is suspended BEFORE trying to resume it | |
| while (!ctx.isSuspended()) { | |
| LockSupport.parkNanos(TimeUnit.MILLISECONDS.toNanos(1)); | |
| } | |
| serializerFactory.newThread(() -> { | |
| sequence.add(3); | |
| }).start(); | |
| // give enough time for the previous vThread to start and try to run | |
| LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1)); | |
| ctx.resume(); | |
| }); | |
| sequence.add(1); | |
| ctx.suspend(); | |
| sequence.add(2); | |
| }).start(); | |
| long now = System.currentTimeMillis(); | |
| while (true) { | |
| assertTrue(System.currentTimeMillis() - now < 20_000); | |
| if (sequence.size() == 3) { | |
| assertEquals(List.of(1, 2, 3), sequence); | |
| break; | |
| } | |
| Thread.sleep(1); | |
| } | |
| } | |
| } |
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