CODEWITHSUNDEEP
javajmxmxbean
Bass
Bass

Reputation: 5328

NPE when unregistering an MXBean from multiple MBean servers

I have an MXBean instance which is registered in 2 MBean servers:

@MXBean(true)
public interface I {
    // ...
}

public final class C extends StandardMBean implements I {
    public C() {
        super(I.class, JMX.isMXBeanInterface(I.class));
    }

    public static void main(final String args[]) throws JMException, IOException {
        final MBeanServer mBeanServer0 = ManagementFactory.getPlatformMBeanServer();
        final MBeanServer mBeanServer1 = MBeanServerFactory.createMBeanServer();

        final ObjectName objectName = new ObjectName("com.example:name=Foo,type=Bar");
        final I i = new C();
        mBeanServer0.registerMBean(i, objectName);
        mBeanServer1.registerMBean(i, objectName);
        // ...
    }
}

The StandardMBean instance wraps an instance of MXBeanSupport. I want to unregister my MBean from both servers later on:

mBeanServer1.unregisterMBean(objectName);
mBeanServer0.unregisterMBean(objectName);

The problem is, unregister() method of MXBeanSupport has the following implementation and obviously can only be called once:

@Override
public void unregister() {
    synchronized (lock) {
        if (mxbeanLookup != null) {
            if (mxbeanLookup.removeReference(objectName, getResource()))
                objectName = null;
        }
    }
}

Otherwise, I'm getting an NPE wrapped into a RuntimeMBeanException:

Exception in thread "main" javax.management.RuntimeMBeanException: RuntimeException thrown in postDeregister method: rethrowing <java.lang.NullPointerException>, although the MBean is sucessfully unregistered
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.postDeregisterInvoke(DefaultMBeanServerInterceptor.java:1060)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.exclusiveUnregisterMBean(DefaultMBeanServerInterceptor.java:452)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.unregisterMBean(DefaultMBeanServerInterceptor.java:415)
    at com.sun.jmx.mbeanserver.JmxMBeanServer.unregisterMBean(JmxMBeanServer.java:546)
    at com.example.C.main(C.java:41)
Caused by: java.lang.NullPointerException
    at com.sun.jmx.mbeanserver.MXBeanLookup.removeReference(MXBeanLookup.java:159)
    at com.sun.jmx.mbeanserver.MXBeanSupport.unregister(MXBeanSupport.java:169)
    at javax.management.StandardMBean.postDeregister(StandardMBean.java:1137)
    at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.postDeregisterInvoke(DefaultMBeanServerInterceptor.java:1054)
    ... 4 more

Still, unregistering an MBean from a single server only is not an option.

How should I correct my code w/o creating two separate MBean instances?

Upvotes: 1

Views: 478

Answers (1)

Woot4Moo
Woot4Moo

Reputation: 24336

It appears as though MBeans are global based on the name, so therefore you would not ever be able to register from a "single instance" and instead you would un-register from all available contexts.

    mBeanServer1.unregisterMBean(objectName);
    mBeanServer0.unregisterMBean(objectName);  // this call is superfluous

Upvotes: 0

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