Hello,
i have quite a problem with pthreads (linux 2.4.22).
Scenario:
My process creates a thread using pthread_create().
Thread A is the one communicating with the network (using select() ),
Thread B does some work for Thread A.
Now i need the following:
- Thread A must be able to wake Thread B when there's some work to do.
I'm doing this via pthread_kill() and sigwait(). This works just fine.
- Thread B must be able to wake Thread A from its select() call,
so Thread A can accept the data that has been processed by Thread B.
And this does _not_ work.
I have even tried not using signals but using select() in both threads
and a "fake pipe" for them to be able to wake each other from their
select() calls, but this does not work either.
My code looks about as follows (error checks removed):
pthread_create(&worker_tid, (pthread_attr_t *)NULL,
(void *)worker_thread, NULL);
consumer_thread();
void worker_thread() {
sleep_2_seconds();
printf("worker: waking consumer\n");
wake_consumer();
printf("worker: woke consumer\n");
}
void consumer_thread() {
init_consumer_signals();
..
timeout.tv_sec = 3;
timeout.tv_usec = 0;
..
printf("consumer going to sleep!\n");
ret = select(maxfd+1, &rfd, &wfd, 0, &timeout);
printf("consumer thread just woke up!\n");
..
}
void init_consumer_signals() {
struct sigaction action;
sigset_t set;
sigemptyset(&action.sa_mask);
action.sa_flags = SA_RESTART;
/* also does not work without SA_RESTART */
action.sa_handler = consumer_setflag;
/* neither select() returns, nor is this signal
* handler executed..!
*/
sigaction(SIGUSR1, &action, NULL);
sigemptyset(&set);
sigaddset(&set, SIGUSR1);
pthread_sigmask(SIG_UNBLOCK, &set, NULL);
}
void wake_consumer() {
pid_t pid;
pid = getpid();
/* have also tried pthread_kill with a cast, did not work.
* where do i get the pthread_t of the consumer from? dp
* i readlly need to create _another_ thread, leaving the
* creating thread just idle, just to get a thread id?
*/
kill(pid, SIGUSR1);
}
Help/suggestions appreciated.
Maybe some of you know some open source applications that use pthreads and
a similar communication model, if so please tell me about them so i can
take a look at the code. In case there's a much more elegant way to do
this, i'd be interested in hearing about it.
Thanks for your help and contribution!
Greetings
Marc Roessler
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