import java.lang.management.ManagementFactory;

import java.util.concurrent.atomic.AtomicInteger;

import javax.management.Attribute;

import javax.management.JMX;

import javax.management.MBeanServer;

import javax.management.Notification;

import javax.management.NotificationListener;

import javax.management.ObjectName;

import javax.management.monitor.StringMonitor;

import javax.management.monitor.StringMonitorMBean;

public class StringMonitorDeadlockTest {

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

if (args.length != 1)

throw new Exception("Arg should be test number");

int testNo = Integer.parseInt(args[0]) - 1;

TestCase test = testCases[testNo];

System.out.println("Test: " + test.getDescription());

test.run();

System.out.println("Test passed");

}

private static enum When {IN_GET_ATTRIBUTE, IN_NOTIFY};

private static abstract class TestCase {

TestCase(String description, When when) {

this.description = description;

this.when = when;

}

void run() throws Exception {

final MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();

final ObjectName observedName = new ObjectName("a:b=c");

final ObjectName monitorName = new ObjectName("a:type=Monitor");

mbs.registerMBean(new StringMonitor(), monitorName);

final StringMonitorMBean monitorProxy =

JMX.newMBeanProxy(mbs, monitorName, StringMonitorMBean.class);

final TestMBean observedProxy =

JMX.newMBeanProxy(mbs, observedName, TestMBean.class);

final Runnable sensitiveThing = new Runnable() {

public void run() {

doSensitiveThing(monitorProxy, observedName);

}

};

final Runnable nothing = new Runnable() {

public void run() {}

};

final Runnable withinGetAttribute =

(when == When.IN_GET_ATTRIBUTE) ? sensitiveThing : nothing;

mbs.registerMBean(new Test(withinGetAttribute), observedName);

monitorProxy.addObservedObject(observedName);

monitorProxy.setObservedAttribute("Thing");

monitorProxy.setStringToCompare("old");

monitorProxy.setGranularityPeriod(10L); // 10 ms

monitorProxy.setNotifyDiffer(true);

monitorProxy.start();

final int initGetCount = observedProxy.getGetCount();

int getCount = initGetCount;

for (int i = 0; i < 500; i++) { // 500 * 10 = 5 seconds

getCount = observedProxy.getGetCount();

if (getCount != initGetCount)

break;

Thread.sleep(10);

}

if (getCount <= initGetCount)

throw new Exception("Test failed: presumable deadlock");

// This won't show up as a deadlock in CTRL-\ or in

// ThreadMXBean.findDeadlockedThreads(), because they don't

// see that thread A is waiting for thread B (B.join()), and

// thread B is waiting for a lock held by thread A

// Now we know the monitor has observed the initial value,

// so if we want to test notify behaviour we can trigger by

// exceeding the threshold.

if (when == When.IN_NOTIFY) {

final AtomicInteger notifCount = new AtomicInteger();

final NotificationListener listener = new NotificationListener() {

public void handleNotification(Notification n, Object h) {

Thread t = new Thread(sensitiveThing);

t.start();

try {

t.join();

} catch (InterruptedException e) {

throw new RuntimeException(e);

}

notifCount.incrementAndGet();

}

};

mbs.addNotificationListener(monitorName, listener, null, null);

observedProxy.setThing("new");

for (int i = 0; i < 500 && notifCount.get() == 0; i++)

Thread.sleep(10);

if (notifCount.get() == 0)

throw new Exception("Test failed: presumable deadlock");

}

}

abstract void doSensitiveThing(StringMonitorMBean monitorProxy,

ObjectName observedName);

String getDescription() {

return description;

}

private final String description;

private final When when;

}

private static final TestCase[] testCases = {

new TestCase("Remove monitored MBean within monitored getAttribute",

When.IN_GET_ATTRIBUTE) {

@Override

void doSensitiveThing(StringMonitorMBean monitorProxy,

ObjectName observedName) {

monitorProxy.removeObservedObject(observedName);

}

},

new TestCase("Stop monitor within monitored getAttribute",

When.IN_GET_ATTRIBUTE) {

@Override

void doSensitiveThing(StringMonitorMBean monitorProxy,

ObjectName observedName) {

monitorProxy.stop();

}

},

new TestCase("Remove monitored MBean within threshold listener",

When.IN_NOTIFY) {

@Override

void doSensitiveThing(StringMonitorMBean monitorProxy,

ObjectName observedName) {

monitorProxy.removeObservedObject(observedName);

}

},

new TestCase("Stop monitor within threshold listener",

When.IN_NOTIFY) {

@Override

void doSensitiveThing(StringMonitorMBean monitorProxy,

ObjectName observedName) {

monitorProxy.stop();

}

},

};

public static interface TestMBean {

public String getThing();

public void setThing(String thing);

public int getGetCount();

}

public static class Test implements TestMBean {

public Test(Runnable runWithinGetAttribute) {

this.runWithinGetAttribute = runWithinGetAttribute;

}

public String getThing() {

Thread t = new Thread(runWithinGetAttribute);

t.start();

try {

t.join();

} catch (InterruptedException e) {

throw new RuntimeException(e);

}

getCount++;

return thing;

}

public void setThing(String thing) {

this.thing = thing;

}

public int getGetCount() {

return getCount;

}

private final Runnable runWithinGetAttribute;

private volatile int getCount;

private volatile String thing;

}

}