pthread_kill ends calling program

Question

I am working on Ubuntu 12.04.2 LTS. I have a strange problem with pthread_kill(). The following program ends after writing only "Create thread 0!" to standard output. The program ends with exit status 138.

If I uncomment "usleep(1000);" everything executes properly. Why would this happen?

#include <nslib.h>

void *testthread(void *arg);

int main() {

    pthread_t tid[10];
    int i;

    for(i = 0; i < 10; ++i) {
        printf("Create thread %d!\n", i);
        Pthread_create(&tid[i], testthread, NULL);
        //usleep(1000);
        Pthread_kill(tid[i], SIGUSR1);
        printf("Joining thread %d!\n", i);
        Pthread_join(tid[i]);
        printf("Joined %d!", i);
    }

    return 0;
}

void sighandlertest(int sig) {

    printf("print\n");
    pthread_exit();
    //return NULL;

}

void* testthread(void *arg) {

    struct sigaction saction;

    memset(&saction, 0, sizeof(struct sigaction));
    saction.sa_handler = &sighandlertest;
    if(sigaction(SIGUSR1, &saction, NULL) != 0 ) {
        fprintf(stderr, "Sigaction failed!\n");
    }
    printf("Starting while...\n");
    while(true) {

    }

    return 0;

}

alk · Answer 1 · 2013-06-03T11:24:15.453

If the main thread does not sleep a bit before raising the SIGUSR1, the signal handler for the thread created most propably had not been set up, so the default action for receiving the signal applies, which is ending the process.

Using sleep()s to synchronise threads is not recommended as not guaranteed to be reliable. Use other mechanics here. A condition/mutex pair would be suitable.

Declare a global state variable int signalhandlersetup = 0, protect access to it by a mutex, create the thread, make the main thread wait using pthread_cond_wait(), let the created thread set up the signal handle for SIGUSR1, set signalhandlersetup = 0 and then signal the condition the main thread is waiting on using pthread_signal_cond(). Finally let the main thread call pthread_kill() as by your posting.

pthread_kill ends calling program

1 Answers1