After starting to use the new machine, I noticed that I started getting bit by an optization where loop control, boolean value tests are being yanked out of the loop.

The basic structure of the problematic software is as follows.

class MyClass ... implements Runnable {
    private boolean stopping;
    public void stop() {
        stopping = true;
        // maybe close a socket etc.
    }

    public void run() {
        while( !stopping ) {
            try {
                ... do some work ...
            } catch( Exception ex ) {
                ... process exception ...
            }
        }
    }
}

What I am seeing is that HotSpot is apparently (this I have gleened from conversations on Doug Lea's Concurrency-Interest list) yanking the while( !stopping) { } block out and replacing it with an if( !stopping ) { } block surrounding a while(true) { } block!

class MyClass ... implements Runnable {
    private boolean stopping;
    public void stop() {
        stopping = true;
        // maybe close a socket etc.
    }

    public void run() {
        if( !stopping ) {
            while(true) {
                try {
                    ... do some work ...
                } catch( Exception ex ) {
                    ... process exception ...
                }
            }
        }
    }
}

The end result, of course, is that a call to stop(); will never be able to stop the looping thread executing in run(){ }.

What I've found, of course, is that if I go ahead and declare stopping as volatile that suddenly the code works as expected!

I ran this code for a long time on a single processor laptop on JSE1.5 even, and don't recall that I saw this happening. I wonder if this optimization only happens on MP machines.