how to terminate a sleeping thread in pthread?

Question

I have thread which sleeps for a long time, then wakes up to do something, then sleep again, like this:

while(some_condition)
{
    // do something
    sleep(100         


        

Answer 1

The classic UNIX condition variable is the self-pipe.

int fds[2];
pipe2(fds, O_NONBLOCK);  // requires newish kernel and glibc; use pipe + 2*fcntl otherwise

child:
    while (some_condition) {
        // do something
        struct pollfd pd = { .fd = fds[0], .events = POLLIN };
        int rc;
        char c;
        while ((rc = poll(&pd, 1, 1000000)) == -1 && errno == EINTR)
            // not entirely correct; 1000000 should be decreased according to elapsed time when repeating after a signal interruption
            ;
        if (rc > 0 && (pd.revents & POLLIN) && read(fds[0], &c, 1) >= 0)
            break;
    }

parent:
    cancel() {
        char c = 0;
        write(fds[1], &c, 1);
    }

Yeah, it's a lot of fiddly (and untested) code. You should probably just use pthread_cond_wait, it requires a pthread_mutex_t and a pthread_cond_t but is much easier.