jdk-24/test/jdk/javax/management/Introspector/ClassLeakTest.java

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/*
 * @test
 * @bug 4909536
 * @summary Ensure that the Introspector does not retain refs to classes
 * @requires vm.opt.final.ClassUnloading
 * @author Eamonn McManus
 *
 * @run clean ClassLeakTest
 * @run build ClassLeakTest
 * @run main/othervm ClassLeakTest
 */

import java.lang.management.ManagementFactory;
import java.lang.ref.WeakReference;
import java.io.File;
import java.nio.file.Paths;
import java.net.*;
import java.util.*;

import javax.management.*;
import javax.management.loading.*;

public class ClassLeakTest {
    public static void main(String[] args) throws Exception {
        System.out.println("Testing that registering and unregistering a " +
                           "Standard MBean does not retain a reference to " +
                           "the MBean's class");

        String[] cpaths = System.getProperty("test.classes", ".")
                                .split(File.pathSeparator);
        URL[] urls = new URL[cpaths.length];
        for (int i=0; i < cpaths.length; i++) {
            urls[i] = Paths.get(cpaths[i]).toUri().toURL();
        }

        Test loaderMBean = new Test(urls);
        Class<?> shadowClass = loaderMBean.loadClass(TestMBean.class.getName());
        if (shadowClass == TestMBean.class) {
            System.out.println("TEST INVALID: MBean got original " +
                               "TestMBean not shadow");
            System.exit(1);
        }
        shadowClass = null;

        MBeanServer mbs = MBeanServerFactory.createMBeanServer();
        ObjectName loaderMBeanName = new ObjectName("x:name=loader");
        mbs.registerMBean(loaderMBean, loaderMBeanName);

        ObjectName testName = new ObjectName("x:type=test");
        mbs.createMBean(Test.class.getName(), testName, loaderMBeanName);

        ClassLoader testLoader = mbs.getClassLoaderFor(testName);
        if (testLoader != loaderMBean) {
            System.out.println("TEST INVALID: MBean's class loader is not " +
                               "MLet: " + testLoader);
            System.exit(1);
        }
        testLoader = null;

        MBeanInfo info = mbs.getMBeanInfo(testName);
        MBeanAttributeInfo[] attrs = info.getAttributes();
        if (attrs.length != 1 || !attrs[0].getName().equals("A")
            || !attrs[0].isReadable() || !attrs[0].isWritable()
            || attrs[0].isIs() || !attrs[0].getType().equals("int")) {
            System.out.println("TEST FAILED: unexpected MBeanInfo attrs");
            System.exit(1);
        }
        MBeanOperationInfo[] ops = info.getOperations();
        if (ops.length != 1 || !ops[0].getName().equals("bogus")
            || ops[0].getSignature().length > 0
            || ops[0].getImpact() != MBeanOperationInfo.UNKNOWN
            || !ops[0].getReturnType().equals("void")) {
            System.out.println("TEST FAILED: unexpected MBeanInfo ops");
            System.exit(1);
        }
        if (info.getConstructors().length != 2) {
            System.out.println("TEST FAILED: wrong number of constructors " +
                               "in introspected bean: " +
                               Arrays.asList(info.getConstructors()));
            System.exit(1);
        }
        if (!info.getClassName().endsWith("Test")) {
            System.out.println("TEST FAILED: wrong info class name: " +
                               info.getClassName());
            System.exit(1);
        }

        WeakReference mbeanRef = new WeakReference(loaderMBean);
        mbs.unregisterMBean(testName);
        mbs.unregisterMBean(loaderMBeanName);
        loaderMBean = null;

        System.out.println("MBean registered and unregistered, waiting for " +
                           "garbage collector to collect class loader");
        for (int i = 0; i < 10000 && mbeanRef.get() != null; i++) {
            System.gc();
            Thread.sleep(1);
        }

        if (mbeanRef.get() == null)
            System.out.println("Test passed: class loader was GC'd");
        else {
            System.out.println("TEST FAILED: class loader was not GC'd");
            System.exit(1);
        }
    }

    public static interface TestMBean {
        public void bogus();
        public int getA();
        public void setA(int a);
    }

    public static class Test extends URLClassLoader implements TestMBean, PrivateClassLoader {
        public Test() {
            super(new URL[0], null);
        }
        public Test(URL[] urls) {
            super(urls, null);
        }
        public void bogus() {}
        public int getA() {return 0;}
        public void setA(int a) {}
    }
}