Threads - Acquiring the lock - Chapter 9 - Question 9

[Glen Iris]

Hello Again Friends,

public static synchronized void main(String args[]) throws InterruptedException{

	Thread t = new Thread();
	t.start();
	System.out.println("X");
	t.wait(10000);
	System.out.println("Y");
}

As it stands, the code will not compile as the code does not acquire a lock on t before calling t.wait();

What changes need to be made on this code for it to compile. In other words, how do I acquire the lock on t?

Thanks

[Anayonkar Shivalkar]

Try

synchronized(t) {
t.wait(10000);
}

instead of

t.wait(10000);

[Dan Drillich]

Glen Iris wrote:
As it stands, the code will not compile as the code does not acquire a lock on t before calling t.wait();

The code compiles for me just fine.

Regards,
Dan

[Sebanti Sanyal]

As it stands, the code will not compile as the code does not acquire a lock on t before calling t.wait();

No, it will compile but result in a run-time exception.

[Anayonkar Shivalkar]

The code will compile, but will throw a java.lang.IllegalMonitorStateException.

[Dan Drillich]

Anayonkar Shivalkar wrote:Try

synchronized(t) {
t.wait(10000);
}

instead of

t.wait(10000);

This works!

[Tommy Delson]

Anayonkar Shivalkar wrote:The code will compile, but will throw a java.lang.IllegalMonitorStateException.

It throws an IllegalMonitorStateException simply because thread "t" calling the wait() method doesn't own the lock with a synchronize(t){...} code block.


In reference to Kathy & Bert book on page 787: Thread Interaction (Exam Objective 4.4) 749 750 Chapter 9: Threads

Note that if the thread calling wait() does not own the lock, it will throw an
IllegalMonitorStateException. This exception is not a checked exception,

so you don't have to catch it explicitly. You should always be clear whether a thread
has the lock of an object in any given block of code.

Reread the Thread chapter and do some more examples that will help reinforce your knowledge and enhance your skills.

Hope it help...

[Glen Iris]

Thanks a bunch guys. i had a brain fart and just couldn't think how to 'acquire a lock'.

:-)