IllegalMonitorStateException (not what you think)

[Anonymous]

I am running a multithreaded Java program on an SGI Origin 2000 multiprocessor machine. I am getting an IllegalMonitorStateException even though I am not calling wait/notify/notifyAll. Here is the error:

java.lang.IllegalMonitorStateException: current thread not owner
        at 
        at sim.opt.Processor.gvtBefore(Processor.java:225, Compiled Code)
        at sim.opt.Processor.run(Processor.java:112, Compiled Code)
        at java.lang.Thread.run(Thread.java:484, Compiled Code)

Here is the code:
Processor

221    /**
222    */
223    public void gvtBefore()
224    {
225        if ( !parent.isGVTInProgress() && parent.getGVTCondition() )
226        {
227            parent.initGVT();
228        }
229    }

parent

229    /**
230    */
231    public boolean isGVTInProgress()
232    {
233        synchronized( gvtState )
234        {
235             return gvtInProgress;
236        }
237    }
238
239    /**
240    */
241    public boolean getGVTCondition()
242    {
243        synchronized( gvtState )
244        {
245            return gvt.condition();
246        }
247    }

Any thoughts?

[dan moore]

what's in gvt.condition()?

[Anonymous]

gvt

    /**    */
    public boolean condition()
    {
        if ( ++i == interval )
        {
                i = 0;
                return true;
        }
        else
        {
            return false;
        }
    }

[Anonymous]

I seem to have fixed it. I merely moved the checks into the parent class, and enclosed them in a single synchronized block. This may be more efficient anyway.
There are some similar bugs posted in Sun's bug database. They marked the bugs as not-reproducable, and closed the topic. There may be something subtle about the locks and the short-circuit condition statement that may cause this problem on different multiprocessor architectures.
Relaxed memory models also introduce sublties that must be programmed for. A good, short article is 'Multiprocessor Saftety and Java', by Paul Jakubik, in case anyone is intersted.
I thought I would wrap this up with what I found out. Please let me know if anyone finds anything out more conclusive. Thanks.
...Mike B.