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Deadlock

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In this section, you will learn about deadlock with an example.

Deadlock

     

A situation where a thread is waiting for an object lock that holds by second thread, and this second thread is waiting for an object lock that holds by first thread, this situation is known as Deadlock.

Lets see a situation in the diagram shown below where the deadlock condition is occurred :

In this diagram two threads having the Printing & I/O operations respectively at a time. But Thread1 need to printer that  is hold up by the Thread2, likewise Thread2 need the keyboard that is hold up by the Thread1. In this situation the CPU becomes ideal and the deadlock condition occurs because no one thread is executed until the hold up resources are free. 

The following program demonstrates the deadlock situation:

public class DeadDemo{
  public static void main(String args[]){
  String s1="Dead";
  String s2="Lock";
  MyThread1 m=new MyThread1(s1,s2);
  MyThread2 m1=new MyThread2(s1,s2);
  }
}

class MyThread1 extends Thread{
  String s1;
  String s2;
  MyThread1(String s1, String s2){
  this.s1=s1;
  this.s2=s2;  
  start();
  }

  public void run(){
  while(true){
  synchronized(s1){

  synchronized(s2){
  System.out.println(s1+s2);  
  }
  }
  }
  }
}
class MyThread2 extends Thread{
  String s1;
  String s2;
  MyThread2(String s1,String s2){

  this.s1=s1;
  this.s2=s2;
  start();
  }

  public void run(){
  while(true){
  synchronized(s2){
  
  synchronized(s1){
  System.out.println(s2+s1);
  }
  }
  }
  }
}

Output of the program is:

C:\j2se6\thread>javac DeadDemo.java

C:\j2se6\thread>java DeadDemo
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
LockDead
LockDead
LockDead
LockDead
LockDead
LockDead
LockDead
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
DeadLock
.........
.........

C:\j2se6\thread>

Download this example 

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Posted on: April 17, 2007

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