Version 16

    JMX support for JGroups


    In 2.2.9, JMX support was added to JGroups. There were several design goals:



    - No dependencies on JMX if JMX support is not required. It should be possible to ship a JGroups version without any

    JMX support, and without jmxri.jar (for JDK 1.4.x). Therefore channels and protocols are not turned into MBeans, e.g.

    FD doesn't implement FDMBean. Instead, a parallel MBean and MBeanImpl hierarchy was created, where the MBeanImpl

    delegates to the real protocol. This hierarchy is located in package org.jgroups.jmx.

    For a protocol org.jgroups.protocols.P, there is a corresponding org.jgroups.jmx.protocols.PMBean

    MBean and an implementation org.jgroups.jmx.protocols.P


    - No negative effect on performance, minimal effect on memory. JMX support can be disabled in the channel, and

    all protocols (stats="false")


    - Support for running in a pre-JMX JDK (1.4, for example), e.g. under JBoss. There is a jgroups-service target in

    the ANT build which generates a jgroups-service.sar that can be deployed into JBoss. The channel defines in the

    META-INF/jboss-service.xml file of the SAR defines a JGroups channel MBean, which will automatically create MBeans

    for all protocols and register them with the MBeanServer


    - Support for running in JDK 5 standalone. JDK 5 has JMX support built in. The jconsole tool can be used to inspect the

    MBean hierarchy.

    To programmatically create MBean support for JDK 5, the following code can be used:

    JChannel channel;
    ArrayList servers=MBeanServerFactory.findMBeanServer(null);
    if(servers == null || servers.size() == 0) {
        throw new Exception("No MBeanServers found;" +
                            "\nJmxTest needs to be run with an MBeanServer present, or inside JDK 5");
    MBeanServer server=(MBeanServer)servers.get(0);
    JmxConfigurator.registerChannel(channel, server, "JGroups:channel=" + channel.getChannelName() , true);


    JmxConfigurator has a number of helper methods which register and de-register the channel and/or te protocols

    attached to a given channel.



    Provided information


    Some information provided includes (all info can be reset), besides configuration:

    • UDP: messages sent/received, bytes sent/received (per member)

    • Discovery: manual triggering of discovery

    • NAKACK: retransmissions per member, last N retransmitted messages,

      lowest and highest sequence numbers per member

    • GMS: membership, history of views

    • FD/FD_SOCK: last N suspected members

    • STATE_TRANSFER: number of state requests, total bytes transferred

    • STABLE: manual triggering of STABLE protocol




    Starting with JGroups release 2.7 all jmx information is exposed dynamically through a use of Java annotation mechanism.

    Previous method of jmx support used in releases 2.2.9 up to 2.7 has been deprecated and removed as use of annotations

    provides a much simpler and easier development and maintenance. There are three basic annotation: @MBean, @ManagedAttribute and @ManagedOperation. Developers of custom protocols may use these annotations in order to expose their protocols to jmx agents.


    @MBean is an optional annotation that exposes all public methods in the class hierarchy (excluding Object)

    as MBean operations. If a more fine grained MBean attribute and operation exposure is needed do not use @MBean

    annotation but annotate fields and public methods directly using @ManagedOperation and @ManagedAttribute



    @MBeanAttribute indicates that a public method or a field (any visibility) in an MBean class defines an MBean

    attribute. This annotation can be applied to either a field or a public setter and/or getter method of a public

    class that is itself is optionally annotated with an @MBean annotation, or inherits such an annotation from a



    @MBeanOperation indicates that a method in an MBean class defines an MBean operation.





    The Draw program was modified to support JMX. The following steps describe how to configure and run a JDK 5 VM and

    look at the resulting Draw application via jconsole.

    • Run the Draw program (the JDK needs to be 5 !):

      java org.jgroups.demos.Draw -props c:\fc-fast.xml -jmx

      (the -jmx flag enables registering the Channel and protocols with the MBeanServer)

    • Start jconsole and connect to the local Draw process

    • Under 'MBeans', choose the JGroups channel and browse the channel and the protocols

    • Optional Add the STATS protocol to the top of the stack; it display information about messages sent

      and received



    The following snapshot shows jconsole in action: