Java Tools Tutorials - Herong's Tutorial Examples - v6.23, by Herong Yang
Java Thread Deadlock Demo Program
This section provides a tutorial example of simple deadlock demo program, SimpleDeadLock.java, with 2 threads waiting for each other.
In a tutorial presented earlier, "jstack" was used to print stack traces of all running threads of a given JVM process. But "jstack" can also be used to detect deadlocks inside a given JVM process. The tutorial example below shows you how "jstack" prints deadlock information:
1. Copy and save this Java program,
/* SimpleDeadLock.java * Copyright (c) 2005 HerongYang.com. All Rights Reserved. */ import java.util.*; public class SimpleDeadLock extends Thread { public static Object l1 = new Object(); public static Object l2 = new Object(); private int index; public static void main(String[] a) { Thread t1 = new Thread1(); Thread t2 = new Thread2(); t1.start(); t2.start(); } private static class Thread1 extends Thread { public void run() { synchronized (l1) { System.out.println("Thread 1: Holding lock 1..."); try { Thread.sleep(10); } catch (InterruptedException e) {} System.out.println("Thread 1: Waiting for lock 2..."); synchronized (l2) { System.out.println("Thread 2: Holding lock 1 & 2..."); } } } } private static class Thread2 extends Thread { public void run() { synchronized (l2) { System.out.println("Thread 2: Holding lock 2..."); try { Thread.sleep(10); } catch (InterruptedException e) {} System.out.println("Thread 2: Waiting for lock 1..."); synchronized (l1) { System.out.println("Thread 2: Holding lock 2 & 1..."); } } } } }
2. Compile and run SimpleDeadLock.java. A deadlock will be created immediately between two running threads:
herong> javac SimpleDeadLock.java herong> java SimpleDeadLock Thread 1: Holding lock 1... Thread 2: Holding lock 2... Thread 2: Waiting for lock 1... Thread 1: Waiting for lock 2...
This deadlock is expected - Thread 1 is holding lock 1 and waiting for lock 2, while thread 2 is holding lock 2 and waiting for lock 1.
See the next section on how to use "jstack" to print the deadlock information and stack traces of 2 related threads.
Table of Contents
javac - The Java Program Compiler
java - The Java Program Launcher
jpackage - Binary Package Builder
javadoc - The Java Document Generator
jdeps - The Java Class Dependency Analyzer
jdeprscan - The Java Deprecated API Scanner
jcmd - The JVM Diagnostic Tool
jconsole - Java Monitoring and Management Console
jstat - JVM Statistics Monitoring Tool
JVM Troubleshooting Tools in JDK
jinfo - VM Option Value Checker
jinfo - Changing HotSpot VM Option
jstack - Stack Tracer to Generate Thread Dump
►Java Thread Deadlock Demo Program
jstack - Detecting Java Thread Deadlocks
Printing Histogram of Java Object Heap
jmap - Generating Heap Dump File
jhat - Java Heap Analysis Tool
jhat - Starting Web Server on a Heap Dump File
Listing Instance Counts of All Classes
Browsing Object Instance Values
Searching for Instances with OQL Statements
jhsdb - The Java HotSpot Debugger
jvisualvm (Java VisualVM) - JVM Visual Tool
javap - The Java Class File Disassembler
keytool - Public Key Certificate Tool
jrunscript - Script Code Shell
native2ascii - Native-to-ASCII Encoding Converter