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/*
* Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* @summary MonitorDeadlock creates threads that are deadlocked on
* object monitors.
* @author Mandy Chung
* @build Barrier
*/
import java.lang.management.*;
import java.util.*;
public class MonitorDeadlock {
private final int EXPECTED_THREADS = 3;
private Barrier go = new Barrier(1);
private Barrier barr = new Barrier(EXPECTED_THREADS);
private Object a = new Object();
private Object b = new Object();
private Object c = new Object();
private Thread[] dThreads = new Thread[EXPECTED_THREADS];
public MonitorDeadlock() {
dThreads[0] = new DeadlockingThread("MThread-1", a, b);
dThreads[1] = new DeadlockingThread("MThread-2", b, c);
dThreads[2] = new DeadlockingThread("MThread-3", c, a);
// make them daemon threads so that the test will exit
for (int i = 0; i < EXPECTED_THREADS; i++) {
dThreads[i].setDaemon(true);
dThreads[i].start();
}
}
void goDeadlock() {
// Wait until all threads have started
barr.await();
// reset for later signals
barr.set(EXPECTED_THREADS);
while (go.getWaiterCount() != EXPECTED_THREADS) {
synchronized(this) {
try {
wait(100);
} catch (InterruptedException e) {
// ignore
}
}
}
// sleep a little so that all threads are blocked before notified.
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// ignore
}
go.signal();
}
void waitUntilDeadlock() {
barr.await();
for (int i=0; i < 100; i++) {
// sleep a little while to wait until threads are blocked.
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// ignore
}
boolean retry = false;
for (Thread t: dThreads) {
if (t.getState() == Thread.State.RUNNABLE) {
retry = true;
break;
}
}
if (!retry) {
break;
}
}
}
private class DeadlockingThread extends Thread {
private final Object lock1;
private final Object lock2;
DeadlockingThread(String name, Object lock1, Object lock2) {
super(name);
this.lock1 = lock1;
this.lock2 = lock2;
}
public void run() {
f();
}
private void f() {
synchronized (lock1) {
barr.signal();
go.await();
g();
}
}
private void g() {
barr.signal();
synchronized (lock2) {
throw new RuntimeException("should not reach here.");
}
}
}
void checkResult(long[] threads) {
if (threads.length != EXPECTED_THREADS) {
throw new RuntimeException("Expected to have " +
EXPECTED_THREADS + " to be in the deadlock list");
}
boolean[] found = new boolean[EXPECTED_THREADS];
for (int i = 0; i < threads.length; i++) {
for (int j = 0; j < dThreads.length; j++) {
if (dThreads[j].getId() == threads[i]) {
found[j] = true;
}
}
}
boolean ok = true;
for (int j = 0; j < found.length; j++) {
ok = ok && found[j];
}
if (!ok) {
System.out.print("Returned result is [");
for (int j = 0; j < threads.length; j++) {
System.out.print(threads[j] + " ");
}
System.out.println("]");
System.out.print("Expected result is [");
for (int j = 0; j < threads.length; j++) {
System.out.print(dThreads[j] + " ");
}
System.out.println("]");
throw new RuntimeException("Unexpected result returned " +
" by findMonitorDeadlockedThreads method.");
}
}
}
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