/* Frage: Welcher Thread bekommt SIGCHLD, wenn die Behandlungsfunktion
 * global installiert wird? */

#include <bsd/err.h>
#include <err.h>
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

void handler() {
     printf("handler: %lu\n", pthread_self());
     exit(EXIT_SUCCESS);
}

void *thread(void *forkp) {
     if (forkp) {
          switch (fork()) {
          case -1: err(EXIT_FAILURE, "fork");
          case 0:
               execlp("sleep", "sleep", "1", NULL);
               err(EXIT_FAILURE, "exec");
          }
          printf("forking thread: %lu\n", pthread_self());
     } else {
          printf("regular thread: %lu\n", pthread_self());
     }

     for (;;) pause();
}

int main()
{
     sigset_t mask; sigemptyset(&mask);
     sigaction(SIGCHLD, &((struct sigaction) {
                    .sa_handler = handler,
                    .sa_mask = mask
               }), NULL);

     pthread_t tid;
     for (int i = 0; i < 9; i++)
          pthread_create(&tid, NULL, &thread, NULL);
     pthread_create(&tid, NULL, &thread, (void*) !NULL);

     for (;;) pause();

     return 0;
}

/* ERGEBNIS
 *
 * $ ./sigchld-test
 * regular thread: 139999324866240
 * regular thread: 139999314839232
 * regular thread: 139999160567488
 * regular thread: 139999304812224
 * regular thread: 139999223740096
 * regular thread: 139999213713088
 * regular thread: 139999193659072
 * regular thread: 139999203686080
 * regular thread: 139999183632064
 * forking thread: 139999173605056
 * handler: 139999173605056
 *
 * => Zumindest die Glibc stellt das Signal dem Thread zu, welches den
 *    Prozess erstellt hat.
 */