why people bother to interview here (Part 1)

I have just gotten out of yet another interview with a “senior” Java candidate who doesn’t know threading at all. Please don’t claim you are a senior candidate unless you can answer this basic question.

public class Foo {
    public static final Foo INSTANCE_1 = new Foo();
    public static final Foo INSTANCE_2 = new Foo();

    public static synchronized method1() { /* really long execution */ }
    public        synchronized method2() { /* really long execution */ }
    public static              method3() { /* really long execution */ }
    public                     method4() { /* really long execution */ }
    public static synchronized method5() { /* really long execution */ }
    public        synchronized method6() { /* really long execution */ }
}

Now pretend that there are these threads running on a 64000-core machine. Each thread, at the exact same picosecond, makes a call to the method listed:

    Foo.INSTANCE_1.method1();

    Foo.INSTANCE_1.method2();

    Foo.INSTANCE_1.method3();

    Foo.INSTANCE_1.method4();

    Foo.INSTANCE_1.method5();

    Foo.INSTANCE_1.method6();

    Foo.INSTANCE_1.method1();

    Foo.INSTANCE_1.method2();

    Foo.INSTANCE_1.method3();

    Foo.INSTANCE_1.method4();

    Foo.INSTANCE_1.method5();

    Foo.INSTANCE_1.method6();

    Foo.INSTANCE_2.method1();

    Foo.INSTANCE_2.method2();

    Foo.INSTANCE_2.method3();

    Foo.INSTANCE_2.method4();

    Foo.INSTANCE_2.method5();

    Foo.INSTANCE_2.method6();

    Foo.INSTANCE_2.method1();

    Foo.INSTANCE_2.method2();

    Foo.INSTANCE_2.method3();

    Foo.INSTANCE_2.method4();

    Foo.INSTANCE_2.method5();

    Foo.INSTANCE_2.method6();

    new Foo(){ }.method1();

    new Foo(){ }.method2();

    new Foo(){ }.method3();

    new Foo(){ }.method4();

    new Foo(){ }.method5();

    new Foo(){ }.method6();

Questions:

1. Now which threads will block each other and why?
2. Where are locks stored? (The JVM has to store the information some place!)
3. What is a deadlock?
4. When do deadlocks occur? Does the above code experience a deadlock?

No, the answer is not going to be given.

This post is labeled Part 1 because there will be more rants in this area I am sure!

Update: 12 April 2011: more detailed!