| spuzzzzzzz |
10-18-2004 09:10 PM |
POSIX semaphores acting strangely
I'm writing a threaded program that makes heavy use of POSIX semaphores. I'm running gentoo amd64 with glibc 2.3.4.20040808-r1 (using nptl). The program is too long to explain in its entireity, but here are three sections:
Code:
if(sem_init(&info->post->avail, 0, info->numbufs) != 0
|| sem_init(&info->post->filled, 0, 0) != 0) {
fprintf(stderr, "error initialising semaphores in postfilter\n");
exit_with_error(1);
}
printf("initialised\n");
Code:
printf("about to raise\n");
sem_post(&info->post->filled);
printf("raised\n");
Code:
sem_wait(&info->post->filled);
printf("lowered\n");
These sections of the code are the only sections that touch info->post->filled. Since info->post->filled gets initialised to zero, it should not lower until after it has been raised, right? But this is the output (from within gdb), with *** next to the relevant bits:
Code:
[Thread debugging using libthread_db enabled]
[New Thread 182921540368 (LWP 18332)]
Initialising prefilter...
Initialising fft...
Initialising postfilter...
initialised ***
Initialising drawing...
[New Thread 1082128736 (LWP 18333)]
[New Thread 1090517344 (LWP 18334)]
[New Thread 1098905952 (LWP 18335)]
[New Thread 1107294560 (LWP 18336)]
[New Thread 1115683168 (LWP 18337)]
[New Thread 1124071776 (LWP 18338)]
lowered ***
about to raise ***
raised ***
lowered
about to raise
raised
Can anyone explain this? |
