[GROOVY-8035] Class unloading (PermGen) memory leak with Groovy Shell

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.7
• Fix Version/s: 2.4.8
• Environment: Oracle JDK6, Oracle JDK7
• Assignee: John Wagenleitner
• Reporter: Gernot R. Bauer
• Created: 05/Jan/17 09:35
• Updated: 01/Feb/17 23:18
• Resolved: 09/Jan/17 15:55

Description

The following code causes a memory leak in perm gen reproducibly on Oracle JDK6 and 7.

import groovy.lang.GroovyShell;

public class Demo {


    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 10000000; i++) {
            GroovyShell gs = new GroovyShell();
            Script script = gs.parse(" 'Hello, World';");
            Object result = script.run();
            assert result.equals("Hello, World");
        }
    }
}

Tested with the following VM options (with PermGen size 20MB), the execution results in java.lang.OutOfMemoryError: PermGen space after a little more than 2000 iterations.

-verbose:class -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+CMSClassUnloadingEnabled -XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses -XX:+TraceClassUnloading -XX:MaxPermSize=16M -XX:+UseConcMarkSweepGC -XX:+ExplicitGCInvokesConcurrent -XX:+PrintGCDetails -XX:-UseParNewGC

As a workaround, calling the following method with script.getClass() from above (as described in http://stackoverflow.com/a/41473210/2156613) seems to avoid this leak and trigger class unloading correctly:

    public static void clearAllClassInfo(Class<?> type) {
        try {
            Field globalClassValue = ClassInfo.class.getDeclaredField("globalClassValue");
            globalClassValue.setAccessible(true);
            GroovyClassValue classValueBean = (GroovyClassValue) globalClassValue.get(null);
            classValueBean.remove(type);
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

This should be handled by Groovy itself, or (if this is not possible) there should be at least a possibility to trigger this functionality via a Groovy API call instead of having to create the above method in all applications using Groovy.