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<td class="text-paragraph-pattern-container mobile-resize-text " style="padding: 0px; border-collapse: collapse; padding: 0 0 10px 0"> <p style="margin: 10px 0 0 0; margin-top: 0">I think I got something. I enabled -Djdk.tracePinnedThreads=full as Alan suggested and it flagged one problematic stack trace:</p>
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<pre class="code-java" style="margin: 10px 0 0 0; margin-top: 0; max-height: 30em; overflow: auto; white-space: pre-wrap; word-wrap: normal">
<span class="code-object" style="color: #910091">Thread</span>[#87,ForkJoinPool-1-worker-5,5,CarrierThreads]
java.base/java.lang.VirtualThread$VThreadContinuation.onPinned(VirtualThread.java:180)
java.base/jdk.internal.vm.Continuation.onPinned0(Continuation.java:398)
java.base/jdk.internal.vm.Continuation.yield0(Continuation.java:390)
java.base/jdk.internal.vm.Continuation.yield(Continuation.java:357)
java.base/java.lang.VirtualThread.yieldContinuation(VirtualThread.java:370)
java.base/java.lang.VirtualThread.park(VirtualThread.java:499)
java.base/java.lang.<span class="code-object" style="color: #910091">System</span>$2.parkVirtualThread(<span class="code-object" style="color: #910091">System</span>.java:2606)
java.base/jdk.internal.misc.VirtualThreads.park(VirtualThreads.java:54)
java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:219)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:715)
java.base/java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:938)
java.base/java.util.concurrent.locks.ReentrantLock$Sync.lock(ReentrantLock.java:153)
java.base/java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:322)
ch.qos.logback.core.rolling.RollingFileAppender.rollover(RollingFileAppender.java:186)
ch.qos.logback.core.rolling.RollingFileAppender.subAppend(RollingFileAppender.java:236) <== monitors:1
ch.qos.logback.core.OutputStreamAppender.append(OutputStreamAppender.java:102)
ch.qos.logback.core.UnsynchronizedAppenderBase.doAppend(UnsynchronizedAppenderBase.java:85)
ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:51)
ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:272)
ch.qos.logback.classic.Logger.callAppenders(Logger.java:259)
ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:426)
ch.qos.logback.classic.Logger.filterAndLog_1(Logger.java:402)
ch.qos.logback.classic.Logger.debug(Logger.java:491)
Testcase.lambda$run$0(Testcase.java:37)
java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:577)
java.base/java.util.concurrent.ThreadPerTaskExecutor$ThreadBoundFuture.run(ThreadPerTaskExecutor.java:352)
java.base/java.lang.VirtualThread.run(VirtualThread.java:287)
java.base/java.lang.VirtualThread$VThreadContinuation.lambda$<span class="code-keyword" style="color: #000091">new</span>$0(VirtualThread.java:174)
java.base/jdk.internal.vm.Continuation.enter0(Continuation.java:327)
java.base/jdk.internal.vm.Continuation.enter(Continuation.java:320)</pre>
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</div> <p style="margin: 10px 0 0 0">Here is my interpretation of what is going on:</p>
<ul>
<li>A virtual thread acquires a monitor (synchronized lock) at ch.qos.logback.core.rolling.RollingFileAppender.subAppend(RollingFileAppender.java:236)</li>
<li>It then attempts to rollover() the log file, but this attempts to acquire a ReentrantLock.</li>
<li>For reasons I cannot explain, another thread seems to be holding the ReentrantLock. Because the carrier thread is pinned, it is forced to block.</li>
<li>So the deadlock situation is as follows: One virtual thread is holding the monitor and waiting on the ReentrantLock, and all other threads are waiting to acquire the monitor.</li>
<li>What I don't understand is who is holding onto the ReentrantLock. It's probably another appender, but I can't tell which. This thread must have locked the ReentrantLock first and is now trying to acquire the monitor. Hence, the deadlock.</li>
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