Re: [Lse-tech] Re: multi-queue scheduler update

[Davide Libenzi]

On Friday 19 January 2001 15:23, Mike Kravetz wrote:
> On Fri, Jan 19, 2001 at 02:03:06PM -0800, Davide Libenzi wrote:
> <stuff deleted>
>
> > > void            oneatwork(int thr)
> > > {
> > >     int             i;
> > >     while (!start)              /* don't disturb pthread_create() */
> > >         usleep(10000);
> > >
> > >     actthreads++;
> > >     while (!stop)
> > >     {
> > >         if (count)
> > >             totalwork[thr]++;
> > >
> > >         syscall(158); /* sys_sched_yield() */
> > >     }
> > >     actthreads--;
> > >     pthread_exit(0);
> > > }
> > >
> > > Note that actthreads is a global variable which is being updated
> > > by multiple threads without any form of synchronization.  Because
> > > of this actthreads sometimes never goes to zero after all worker
> > > threads have finished.
> >
> > If all threads complete successfully actthreads has to be zero.
>
> Not as currently coded.  If two threads try to decrement actthreads
> at the same time, there is no guarantee that it will be decremented
> twice.  That is why you need to put some type of synchronization in
> place.

Right, inc & dec are not atomic w/o #LOCK.

- Davide