Barry, You might want to take a look at this: http://stackoverflow.com/questions/2994216/linux-pthread-suspend The solution suggested there (Answer 1) is to use sigwait(). Answer 3, although not the actual solution, explains why the pthread_suspend/pthread_continue-based solution is racy. I think this may be a general issue with the problem, which requires the use of mutexes. What example do you use to test this? I'd like to take a look. Thanks. Dmitry. On Thu, Nov 24, 2011 at 4:10 PM, Jed Brown <[email protected]> wrote:

On Thu, Nov 24, 2011 at 16:01, Barry Smith <[email protected]> wrote:

...

Yes, but they can only get access to that shared variable one at a time: first get's it, then second get's it, then third gets, .... Ok for a couple of cores but not for dozens.

Take a look at src/sys/objects/pthread.c for the various ways we have coded for "waking" the threads. Maybe I am missing something but this is the best Kerry and I could figure out.

What exactly should I be looking at? Can't you have all the threads spin on a normal shared variable (not a mutex) that is only written by the thread that needs to spark them? Or use a fetch-and-add atomic if you want to keep track of how many are running or limit the number? The latter could use a tree to get logarithmic cost, but if they are stored next to each other, you would still have O(P) cache invalidations.