3 Replies Latest reply on Dec 7, 2019 6:18 AM by pmm

    Adding class loading lock to JBoss Modules

    pmm
    pmm Dec 5, 2019 11:15 AM

      We are running into https://bugs.openjdk.java.net/browse/JDK-8232997. In our case this results in a JVM crash when loading custom JFR event classes. The cause seems to be when multiple threads end up calling #defineClass for the same custom JFR event class then JVM crashes. This seems to be caused by a particularity of JBoss Modules in that it doesn't acquire a class loading lock, instead it allows for a small race condition which is handled by catching LinkageError. This does not seem to work for custom JFR event classes (it is fixed in JDK 14).

       

      We are in talks with our vendor to get the fix back ported from JDK 14 to JDK 11 but that may take a while. As a work around we are considering making our own fork of JBoss Modules to do

      synchronized (getClassLoadingLock(name))

      around loading a class to void concurrent calls to #defineClass for the same class. Apart from the possible performance penatly do you see any other problems with this fix?

       

      If you want to reproduce the issue have a look at:

      GitHub - marschall/jfr-crasher: A reproducer for crashing JFR