On Thu, 10 Sep 2026 05:50:29 GMT, Denghui Dong <[email protected]> wrote:
>> Hi, >> >> Please help review this change that fixes crash in >> ThreadSnapshot::initialize. >> >> After [JDK-8323792](https://bugs.openjdk.org/browse/JDK-8323792), we can >> still see the same crash reported in >> [JDK-8374820](https://bugs.openjdk.org/browse/JDK-8374820) and >> [JDK-8346980](https://bugs.openjdk.org/browse/JDK-8346980). >> >> Here is a reproducer: >> >> >> import java.lang.management.ManagementFactory; >> import java.lang.management.ThreadInfo; >> import java.lang.management.ThreadMXBean; >> import java.util.Arrays; >> import java.util.Objects; >> import java.util.concurrent.atomic.AtomicLong; >> import java.util.concurrent.locks.LockSupport; >> >> public class ThreadSnapshotRace { >> >> public static void main(String[] args) throws Exception { >> Thread producer = new Thread(() -> { >> AtomicLong counter = new AtomicLong(); >> long total = 0; >> while (true) { >> long c = counter.incrementAndGet(); >> total++; >> Thread.ofVirtual().name("vthread").start(() -> { >> counter.decrementAndGet(); >> }); >> if (total % 10_000_000 == 0) { >> System.out.println(total); >> } >> if (c >= 20_000_000) { >> do { >> try { >> Thread.sleep(50); >> } catch (Exception e) { >> } >> } while (counter.get() > 0); >> } >> } >> }); >> producer.start(); >> >> Thread.sleep(1000); >> >> Thread consumer = new Thread(() -> { >> ThreadMXBean bean = ManagementFactory.getThreadMXBean(); >> long[] ids = carrierIds(bean); >> while (true) { >> ThreadInfo[] infos = bean.getThreadInfo(ids); >> if (infos.length == 0) { >> System.out.println("?"); >> } >> } >> }); >> consumer.start(); >> } >> >> static long[] carrierIds(ThreadMXBean bean) { >> long[] all = bean.getAllThreadIds(); >> long[] carriers = Arrays.stream(bean.getThreadInfo(all)) >> .filter(Objects::nonNull) >> .filter(ti -> >> ti.getThreadName().startsWith("ForkJoinPool-1-worker")) >> .mapToLong(ThreadInfo::getThreadId) >> .toArray(); >> return carriers; >> } >> } >>... > > Denghui Dong has updated the pull request incrementally with one additional > commit since the last revision: > > add test Running with the extra assert (updated above), I found `SafepointSynchronize::print_safepoint_timeout()` is calling `is_vthread_mounted()` from `JavaThread::print_on` and `Thread::print_on`, which is not safe either. We can fix them here with the same `java_lang_VirtualThread::is_instance()` check, so we can add the assert in `vthread_continuation()`, or I can do that in a separate fix if you prefer. ------------- PR Comment: https://git.openjdk.org/jdk/pull/32788#issuecomment-5627603982
