Question

can not reproduce deadlock using the next code

I am trying yo get a deadlock using the next code,
but it seems that it works good.

Please see below:

public class Deadlock {

    static Object lock1 = new Object();
    static Object lock2 = new Object();

    public static void main(String[] args) {

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    synchronized (lock1) {
                        System.out.println("Thread 1: locked lock1");
                    }
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (lock2) {
                        System.out.println("Thread 1: locked lock2");
                    }
                }
            }
        }).start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    synchronized (lock2) {
                        System.out.println("Thread 2: locked lock2");
                    }
                    try {
                        Thread.sleep(50);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    synchronized (lock1) {
                        System.out.println("Thread 2: locked lock1");
                    }
                }
            }
        }).start();

    }

}

What I don’t understand in this case or what’s wrong in this code?

Answer 1

Why would the above code cause a deadlock? Each thread only locks one lock at a time, so if the other thread tries to lock it, it just has to wait for the first one to release it.

You would have a serious risk of deadlock if the threads did

synchronized (lock1) {
    synchronized (lock2) {
        ...
    }
}

and

synchronized (lock2) {
    synchronized (lock1) {
        ...
    }
}