Java Tutorial/Thread/Deadlock

An example of deadlock.

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();
  }
}

Deal with lock

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");
      }
    }
  }
}