Re: [Fwd: Possible bug in Thread.start()]

Archie Cobbs wrote:
> Chris Pickett wrote:
> 
>> Etienne Gagnon wrote:
>>
>>> -------- Original Message --------
>>> Subject: Possible bug in Thread.start()
>>> Date: Mon, 13 Dec 2004 17:38:47 -0600
>>> From: Archie Cobbs <[email protected]>
>>> To: old mailing-list
>>>
>>> Hello Sablevm folks,
>>>
>>> I recently discovered a bug in JC that may also apply to SableVM,
>>> because JC's thread handling is based on SableVM.
>>>
>>> The bug is a race condition between thread #1 stopping the world
>>> and thread #2 creating a new thread via Thread.start().
>>
>>
>> Thanks Archie, I've chased bugs related to thread startup in the GC 
>> stuff before (threads will reach the "impossible control flow" case), 
>> but never managed to nail it.
> 
> 
> Well hopefully this is it. By the way, here is the test program
> that I was using to trigger the bug in JC. Maybe you can try it
> with SableVM "before and after" the bug fix.

I tried your test program, but it didn't crash SableVM, either before or 
after the patch.  I had to hit CTRL-C to stop it, but I think that was 
intentional.

It does however fix crashing in the attached program, which is great.  I 
ran this program 100 times with:

$ for num in `seq 1 100`; do sablevm -Y ThreadStarter; done

and without your patch it would segfault one or two times in 100.

Cheers,
Chris

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/* attempts two different ways to start threads.
   
   note that none of:

     a) way 1; way 1;
     b) way 2; way 2;
     c) way 2; way 1;
 
   were observed to fail, with 100+ runs, whereas

     d) way 1; way 2;

   fails about 5 percent of the time on
   tofu.cs.mcgill.ca (2P).

   (if you make things more complex by adding another
    Runnable implementation, it fails more often, but
    this was the most stripped down I could get it)
*/

public class ThreadStarter {
    
    public ThreadStarter() {
    }    
    
    public static void main(String[] argv) {
	
	Runnable myRunnable;
	Thread myThread;  

	/* way 1 */
	myRunnable = new IncrementRunnable();
	myThread = new Thread(myRunnable);
	myThread.start();

	/* way 2 */
	myRunnable = new IncrementRunnable();
	myRunnable.run();
    }
}

class IncrementRunnable implements Runnable {

    private int k = 0;

    public IncrementRunnable() {
    }

    public void run() {
	for(int i=0;i<100;i++) {
	    k++;
	}
    }
}