Fwd: Class initialization pinning deadlock with Log4j 2

Mon Nov 3 18:08:13 UTC 2025

Hi Danny,

I see a couple of FJP workers that don’t seem to be carrying a virtual 
thread blocked on clinit. Do you have the full stacktraces? If 
available, the native stack traces would also be useful to verify the 
entry point into the VM for the ones blocked at clinit.

Thanks,
Patricio

On 11/2/25 9:44 PM, Danny Thomas wrote:
> 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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