Overview

This project replicates the problem described in LBCORE-224 without being dependent on either Logback or ZooKeeper.

Something seems to be broken concerning locks in general and/or ReentrantReadWriteLock.

The entry in the Java Bug Database is (or rather: will be) #7099601.

Background Information

The files contained in the lib were created based on http://svn.apache.org/repos/asf/zookeeper/trunk/ rev 1178579.

According to LBCORE-224 running the tests multiple times will fail very mysteriously on some systems (at least Windows and Mac) with Java 1.6.x.

It currently looks like only IDEA/Eclipse and Maven are able to reproduce it. Gradle seems to be immune for unknown reasons.

The supposedly problematic code in AppenderAttachableImpl looks like this:

public int appendLoopOnAppenders(E e) {
  int size = 0;
  r.lock();
  try {
    for (Appender<E> appender : appenderList) {
      appender.doAppend(e);
      size++;
    }
  } finally {
    r.unlock();
  }
  return size;
}

The following exception is thrown:

java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantReadWriteLock$Sync.tryReleaseShared(ReentrantReadWriteLock.java:363)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1317)
    at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.unlock(ReentrantReadWriteLock.java:745)
    at ch.qos.logback.core.spi.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:68)

As you can see in the snippet above, there is no way that the lock should be able to unlock without being locked before. Taking a look at the source of AppenderAttachableImpl you'll also see that any other code referencing r looks correct, too.

Please see issue LBCORE-224 for some more informations.

Maven

Execute mvn clean install. This should result in a failed test.

Gradle

Interestingly, Gradle build works as expected without throwing an exception.

Building

Execute either gradlew.bat (windows) or ./gradlew (anything else).

IDEA

Execute either gradlew.bat idea (windows) or ./gradlew idea (anything else) to generate IDEA project files.

This will execute the test. If the build does not fail it means that this bug did not show up. Try it multiple times.

Eclipse

Execute either gradlew.bat eclipse (windows) or ./gradlew eclipse (anything else) to generate Eclipse project files.

First hints...

Given that testing with Gradle works but the identical test fails in both Maven and IDEA, this issue may be related to some difference in the way the tests are executed.

Part of Gradle stacktrace

at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecuter.execute(JUnitTestClassExecuter.java:51)
at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassProcessor.processTestClass(JUnitTestClassProcessor.java:63)
at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:49)

Part of IDEA stacktrace

at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:71)

Part of Maven stacktrace

at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
at org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:35)