Understanding thread behavior

24 Jan 2007 12:06:27 -0800
I've taken a "deadlock" sample from a java Sun tutorial page and
modified it slightly. It's exhibiting some behavior that I find

Here is the sample code. Keep in mind that it's supposed to deadlock.

public class Deadlock {
    static class Friend {
        private final String name;
        public Friend(String name) {
            this.name = name;
        public String getName() {
            return this.name;
        public synchronized void step1(Friend thefriend) {
            System.out.println(this.name + " : locked by: " +
            System.out.println(this.name + " : trying to get lock
on: " + thefriend.getName());
            System.out.println(this.name + " : released lock on: " +
        public synchronized void step2(Friend thefriend) {
            System.out.println(this.name + " : locked by " +

    public static void main(String[] args) {

        System.out.println("There are two separate locks involved
        System.out.println("One lock is for the 'Bob' object, and one
for the 'Roberts' object");

        final Friend bob = new Friend("Bob");
        final Friend roberts = new Friend("Roberts");

        new Thread(new Runnable() {
            public void run() { bob.step1(roberts); }

        new Thread(new Runnable() {
            public void run() { roberts.step1(bob); }

Note the three System calls in main. If the System calls are present,
the code will execute and NO deadlock will occur (95% of the time...).
If I take out the System calls, the deadlock occurs as expected nearly
100% of the time.

I don't know much about JVMs and Java in general. This was a learning
exercise. Can someone give me a
reasonable explanation of why adding the System calls before any
objects are even created, might cause timing
issues that would throw off the deadlock?

I'm a bit at a loss here...

Any input is appreciated. Thanks!


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