On Thursday 17 July 2008 01:42:31 pm Michael B Allen wrote: > On Thu, Jul 17, 2008 at 10:05 AM, John Baldwin <[EMAIL PROTECTED]> wrote: > > On Saturday 12 July 2008 07:11:26 pm Michael B Allen wrote: > >> Hi, > >> > >> Below is a semtimedop(2) implementation that I'm using for FreeBSD. I > >> was hoping someone could look it over and tell me if they think the > >> implementation is sound. > >> > >> The code seems to work ok but when stressing the FreeBSD build of my app > >> I have managed to provoke errors related to concurrency (usually when a > >> SIGALRM goes off). The Linux build works flawlessesly so I'm wondering > >> about this one critical function that is different. > >> > >> Do you think it would make any difference if I used > >> ITIMER_VIRTUAL / SIGVTALRM instead of ITIMER_REAL / SIGALRM? > >> > >> Or perhaps I should be using a different implementation entirely? > > > > What specific races are you seeing? The timer is firing too early, too > > late? > > It's very difficult to tell. I can only trigger the issue very > occasionally running my torture test such that any diagnostic logging > changes the results. > > And at this point I'm not sure my semtimedop implementation is > responsible. I have not seen the issue since fixing the race pointed > out by Mikko (although I have not tried very hard to provoke it). > > For now, I'm satisfied since I do not think the issue will be > triggered in the wild. I hate to use signals for anything but as much > as I try, there's just no other way to implement semtimedop within a > single largely self-contained function. In the future I will likely > use another process in the application that uses select(2) as an > "event service" to post on semaphores after a certain time period. > Unfortunately, right now, that service ultimately calls semtimedop so > I'll save it for a rainy day. > > Although if you implemented semtimedop(2) into the FreeBSD API that > would work too :-)
POSIX semaphores (sem_open(3), sem_create(3), etc.) do have a sem_timedwait(3). However, POSIX semaphores have several bugs in 6.x and 7.x (they should work a lot better in 8). If you want I can give you a patch for 6.x or 7.x that backports the 8.x POSIX semaphores. -- John Baldwin _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
