Hi, We have hit the exception mentioned in the subject in one of our applications. We are using JDK 6 and Logback 0.9.14. Here is the stacktrace: Caused by: java.lang.IllegalMonitorStateException at java.util.concurrent.locks.ReentrantReadWriteLock$Sync.tryReleaseShared(ReentrantReadWriteLock.java:363) at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1253) at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.unlock(ReentrantReadWriteLock.java:745) at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:64) at ch.qos.logback.classic.Logger.appendLoopOnAppenders(Logger.java:270) at ch.qos.logback.classic.Logger.callAppenders(Logger.java:257) at ch.qos.logback.classic.Logger.buildLoggingEventAndAppend(Logger.java:439) at ch.qos.logback.classic.Logger.filterAndLog_1(Logger.java:411) at ch.qos.logback.classic.Logger.debug(Logger.java:504) I have checked the code and it seems to me this can only happen if the readLock.lock() method throws an exception: public int appendLoopOnAppenders(E e) { 56<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#56> int size = 0; 57<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#57> try { 58<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#58> r.lock(); 59<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#59> for (Appender<E> appender : appenderList) { 60<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#60> appender.doAppend(e); 61<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#61> size++; 62<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#62> } 63<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#63> } finally { 64<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#64> r.unlock(); 65<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#65> } 66<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#66> return size; 67<http://logback.qos.ch/xref/ch/qos/logback/core/spi/AppenderAttachableImpl.html#67> } if r.lock() in line 58 throws an exception for some reason than in the finally block the unlock will throw also an exception which will hide the original one. I cannot see any other reason why the unlock would throw this exception in this scenario. I am not yet able to reproduce it, but I thought this exception worth a mail. The only suggestion I have for now is to move the r.lock() call out of the try block, because if that is the bad guy, than we would have the original exception propagated. If I have more information on this issue I will update this thread. Regards, Zoltan Szel Morgan Stanley | IDEAS PRACTICE AREAS Lechner Odon fasor 8 | Floor 07 Budapest, 1095 Phone: +36 1 881-3978 Zoli.Szel@MorganStanley.com<mailto:Zoli.Szel@MorganStanley.com> -------------------------------------------------------- NOTICE: If received in error, please destroy and notify sender. Sender does not intend to waive confidentiality or privilege. Use of this email is prohibited when received in error.