Name: agR10195 Date: 02/09/2004


The test below reveals that MemoryPoolMBean.resetPeakUsage() returns null
if the metric is accessed via MBeanServer:

import java.io.*;
import java.util.*;
import java.lang.management.*;
import javax.management.*;

public class Test {
    private static MBeanServer mbeanServer = null;

    public static void main(String[] argv) throws Exception {

        // Register an MBean
        System.setProperty("javax.management.builder.initial", "");
        mbeanServer = ManagementFactory.getPlatformMBeanServer();
        System.out.println("mbeanServer = " + mbeanServer);
            
        // Get all pools that register on the server
        Vector pools = getMemoryPoolMBeansOnServer();
        for (int i = 0; i < pools.size(); i++) {
            ObjectName pool = (ObjectName) pools.get(i);
            System.out.println(i + ": name = " + pool);
            Object object = mbeanServer.invoke(pool, "resetPeakUsage",
                                               null, null);
            MemoryUsage usage = (MemoryUsage) object;
            System.out.println(" usage = " + usage);
            
            object = mbeanServer.getAttribute(pool, "Valid");
            Boolean b = (Boolean) object;
            boolean isValid = b.booleanValue();
            if (usage == null && isValid) {
                System.out.println(" resetPeakUsage() returned null, but the "
                                 + "pool is valid");
            }
        }
    }
    
    public static Vector getMemoryPoolMBeansOnServer() {
        Set set = mbeanServer.queryNames(null, null);
        Vector filteredSet = new Vector();
        Iterator iterator = set.iterator();

        // Filter out non-pool MBeans
        while (iterator.hasNext()) {
            ObjectName object = (ObjectName) iterator.next();
            String name = object.toString();
            String sample = ManagementFactory.MEMORY_POOL_MBEAN_DOMAIN_TYPE
                          + ",name=";

            if (name.startsWith(sample))
                filteredSet.add(object);
        }

        return filteredSet;
    }
}

% ../jdk1.5.0-b37/solaris-sparc/bin/java Test
mbeanServer = com.sun.jmx.mbeanserver.JmxMBeanServer@1e0bc08
0: name = java.lang:type=MemoryPool,name=Eden Space
   usage = null
   resetPeakUsage() returned null, but the pool is valid
1: name = java.lang:type=MemoryPool,name=Code Cache
   usage = null
   resetPeakUsage() returned null, but the pool is valid
2: name = java.lang:type=MemoryPool,name=Tenured Gen
   usage = null
   resetPeakUsage() returned null, but the pool is valid
3: name = java.lang:type=MemoryPool,name=Perm Gen
   usage = null
   resetPeakUsage() returned null, but the pool is valid
4: name = java.lang:type=MemoryPool,name=Survivor Space 1
   usage = null
   resetPeakUsage() returned null, but the pool is valid
5: name = java.lang:type=MemoryPool,name=Survivor Space 2
   usage = null
   resetPeakUsage() returned null, but the pool is valid

null is a valid result for resetPeakUsage(), if the pool is invalid. However,
in this case, null is incorrect result, since all pools are valid. The method
works corrrectly, if the metric is accessed directly.

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