Class initialization pinning deadlock with Log4j 2
Francesco Nigro
nigro.fra at gmail.com
Mon Nov 3 09:05:18 UTC 2025
Hi Danny,
I have recently read https://bugs.openjdk.org/browse/JDK-8369238 shared by
others, which could be relevant
Hope that helped,
Franz
Il lun 3 nov 2025, 03:45 Danny Thomas <dannyt at netflix.com> ha scritto:
> Hi folks,
>
> We saw a clinit deadlock with Log4j 2 and virtual threads recently. It's
> common for libraries to use a mix of static and instance field loggers, so
> seems particularly vulnerable to this kind of deadlock at startup.
>
> I don't recall reading what you have planned for clinit pinning, so
> thought I'd pass on this potentially common real-world deadlock and ask
> what you have in mind for addressing this limitation.
>
> Cheers,
> Danny
>
> Pinned virtual thread holding the clinit lock:
>
> #265 "_internalWorkflowEvaluationQueue_2-workflow-evaluation-worker-0"
> virtual
> java.base/jdk.internal.misc.Unsafe.park(Native Method)
>
> java.base/java.lang.VirtualThread.parkOnCarrierThread(VirtualThread.java:675)
> java.base/java.lang.VirtualThread.park(VirtualThread.java:607)
> java.base/java.lang.System$2.parkVirtualThread(System.java:2643)
>
> java.base/jdk.internal.misc.VirtualThreads.park(VirtualThreads.java:54)
>
> java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:219)
>
> java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:754)
>
> java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1079)
>
> java.base/java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:738)
>
> org.apache.logging.log4j.core.util.internal.InternalLoggerRegistry.getLogger(InternalLoggerRegistry.java:113)
>
> org.apache.logging.log4j.core.util.internal.InternalLoggerRegistry.computeIfAbsent(InternalLoggerRegistry.java:196)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:588)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:561)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:71)
>
> org.apache.commons.logging.LogAdapter$Log4jLog.<init>(LogAdapter.java:159)
>
> org.apache.commons.logging.LogAdapter$Log4jAdapter.createLog(LogAdapter.java:113)
> org.apache.commons.logging.LogAdapter.createLog(LogAdapter.java:95)
> org.apache.commons.logging.LogFactory.getLog(LogFactory.java:67)
> org.apache.commons.logging.LogFactory.getLog(LogFactory.java:59)
>
> org.springframework.data.redis.connection.convert.Converters.<clinit>(Converters.java:69)
>
> org.springframework.data.redis.connection.DefaultStringRedisConnection.<init>(DefaultStringRedisConnection.java:187)
>
> org.springframework.data.redis.connection.DefaultStringRedisConnection.<init>(DefaultStringRedisConnection.java:171)
>
> Unparked but unmounted virtual thread that's next in line for read lock:
>
> #369 "_internalWorkflowEvaluationQueue_1-workflow-evaluation-worker-11"
> virtual
> java.base/java.lang.VirtualThread.park(VirtualThread.java:596)
> java.base/java.lang.System$2.parkVirtualThread(System.java:2643)
>
> java.base/jdk.internal.misc.VirtualThreads.park(VirtualThreads.java:54)
>
> java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:219)
>
> java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:754)
>
> java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireShared(AbstractQueuedSynchronizer.java:1079)
>
> java.base/java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.lock(ReentrantReadWriteLock.java:738)
>
> org.apache.logging.log4j.core.util.internal.InternalLoggerRegistry.getLogger(InternalLoggerRegistry.java:113)
>
> org.apache.logging.log4j.core.util.internal.InternalLoggerRegistry.computeIfAbsent(InternalLoggerRegistry.java:196)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:588)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:561)
>
> org.apache.logging.log4j.core.LoggerContext.getLogger(LoggerContext.java:71)
>
> org.apache.commons.logging.LogAdapter$Log4jLog.<init>(LogAdapter.java:159)
>
> org.apache.commons.logging.LogAdapter$Log4jAdapter.createLog(LogAdapter.java:113)
> org.apache.commons.logging.LogAdapter.createLog(LogAdapter.java:95)
> org.apache.commons.logging.LogFactory.getLog(LogFactory.java:67)
> org.apache.commons.logging.LogFactory.getLog(LogFactory.java:59)
>
> org.springframework.data.redis.connection.AbstractRedisConnection.<init>(AbstractRedisConnection.java:38)
>
> With the core workers all taken up by threads blocked on clinit,
> preventing the continuation for the unparked thread from running:
>
> "ForkJoinPool-2-worker-1" #266 [1606] daemon prio=5 os_prio=0 cpu=233.52ms
> elapsed=2547.44s tid=0x00007fe9f38b4000 nid=1606 waiting on condition
> [0x00007fe9ccde6000]
> java.lang.Thread.State: WAITING (parking)
> at jdk.internal.misc.Unsafe.park(java.base at 21.0.7.0.101/Native Method)
> - parking to wait for <0x0000040009f6d730> (a
> java.util.concurrent.ForkJoinPool)
> --
> "ForkJoinPool-2-worker-2" #267 [1607] daemon prio=5 os_prio=0 cpu=393.88ms
> elapsed=2547.44s tid=0x00007fe9cdbf8000 [0x00007fe9cc465000]
> Carrying virtual thread #357
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> - waiting on the Class initialization monitor for
> org.springframework.data.redis.connection.convert.Converters
> --
> "ForkJoinPool-2-worker-3" #271 [1610] daemon prio=5 os_prio=0 cpu=308.69ms
> elapsed=2547.43s tid=0x00007fe9cdbf8700 [0x00007fe9cc2e2000]
> Carrying virtual thread #367
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> - waiting on the Class initialization monitor for
> org.springframework.data.redis.connection.convert.Converters
> --
> "ForkJoinPool-2-worker-4" #272 [1611] daemon prio=5 os_prio=0 cpu=428.92ms
> elapsed=2547.43s tid=0x00007fe9f5efdf00 [0x00007fe9cc261000]
> Carrying virtual thread #297
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> - waiting on the Class initialization monitor for
> org.springframework.data.redis.connection.convert.Converters
> --
> "ForkJoinPool-2-worker-5" #273 [1612] daemon prio=5 os_prio=0 cpu=347.62ms
> elapsed=2547.42s tid=0x00007fe9cbef7000 nid=1612 waiting on condition
> [0x00007fe9cbee0000]
> java.lang.Thread.State: WAITING (parking)
> at jdk.internal.misc.Unsafe.park(java.base at 21.0.7.0.101/Native Method)
> - parking to wait for <0x0000040009f6d730> (a
> java.util.concurrent.ForkJoinPool)
> --
> "ForkJoinPool-2-worker-6" #316 [1651] daemon prio=5 os_prio=0 cpu=286.41ms
> elapsed=2547.04s tid=0x00007fe9db2f2000 [0x00007fe9ca6c5000]
> Carrying virtual thread #265
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> at java.lang.VirtualThread.runContinuation(java.base at 21.0.7.0.101
> /VirtualThread.java:245)
> --
> "ForkJoinPool-2-worker-7" #317 [1652] daemon prio=5 os_prio=0 cpu=415.34ms
> elapsed=2547.03s tid=0x00007fe9db2f2700 nid=1652 waiting on condition
> [0x00007fe9ca645000]
> java.lang.Thread.State: WAITING (parking)
> at jdk.internal.misc.Unsafe.park(java.base at 21.0.7.0.101/Native Method)
> - parking to wait for <0x0000040009f6d730> (a
> java.util.concurrent.ForkJoinPool)
> --
> "ForkJoinPool-2-worker-8" #359 [1675] daemon prio=5 os_prio=0 cpu=108.86ms
> elapsed=2546.41s tid=0x00007fe9f58fff00 [0x00007fe9c9a69000]
> Carrying virtual thread #270
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> - waiting on the Class initialization monitor for
> org.springframework.data.redis.connection.convert.Converters
> --
> "ForkJoinPool-2-worker-9" #360 [1676] daemon prio=5 os_prio=0 cpu=199.56ms
> elapsed=2546.41s tid=0x00007fea12c4ed00 [0x00007fe9c99e8000]
> Carrying virtual thread #363
> at jdk.internal.vm.Continuation.run(java.base at 21.0.7.0.101
> /Continuation.java:251)
> - waiting on the Class initialization monitor for
> org.springframework.data.redis.connection.convert.Converters
>
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