Java Tutorial/Thread/Deadlock

An example of deadlock.

   <source lang="java">

class A {

 synchronized void foo(B b) {
   String name = Thread.currentThread().getName();
   System.out.println(name + " entered A.foo");
   try {
     Thread.sleep(1000);
   } catch (Exception e) {
     System.out.println("A Interrupted");
   }
   System.out.println(name + " trying to call B.last()");
   b.last();
 }
 synchronized void last() {
   System.out.println("Inside A.last");
 }

} class B {

 synchronized void bar(A a) {
   String name = Thread.currentThread().getName();
   System.out.println(name + " entered B.bar");
   try {
     Thread.sleep(1000);
   } catch (Exception e) {
     System.out.println("B Interrupted");
   }
   System.out.println(name + " trying to call A.last()");
   a.last();
 }
 synchronized void last() {
   System.out.println("Inside A.last");
 }

} class Deadlock implements Runnable {

 A a = new A();
 B b = new B();
 Deadlock() {
   Thread.currentThread().setName("MainThread");
   Thread t = new Thread(this, "RacingThread");
   t.start();
   a.foo(b); // get lock on a in this thread.
   System.out.println("Back in main thread");
 }
 public void run() {
   b.bar(a); // get lock on b in other thread.
   System.out.println("Back in other thread");
 }
 public static void main(String args[]) {
   new Deadlock();
 }

}</source>

Deal with lock

   <source lang="java">

public class DeadlockDemo {

 public static void main(String[] args) throws Exception {
   UseShared s1 = new UseShared("x");
   UseShared s2 = new UseShared("y");
   s1.start();
   s2.start();
   s1.join();
   s2.join();
 }

}

class UseShared extends Thread {

 String s1 = "", s2 = "";
 UseShared(String name) {
   setName(name);
 }
 public void run() {
   for (int i = 0; i < 100; i++) {
     if (getName().equals("x"))
       method1();
     else
       method2();
     try {
       Thread.sleep(1000);
     } catch (Exception e) {
     }
   }
 }
 void method1() {
   synchronized (s1) {
     System.out.println("method1: s1");
     synchronized (s2) {
       System.out.println("method1: s2");
     }
   }
 }
 void method2() {
   synchronized (s2) {
     System.out.println("method2: s1");
     synchronized (s1) {
       System.out.println("method2: s2");
     }
   }
 }

}</source>