Ticket #15193: pselect-test.c

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include <sys/select.h>


void
sigchld_handler(int signum)
{
    puts("SIGCHLD received");
}

int
main(int argc, char **argv)
{
    sigset_t sigchld_sigset, empty_sigset;
    struct sigaction sigchld_action;
    fd_set readfds;
    int psignal_result, psignal_err;


    /* Install a handler for SIGCHLD (so it isn't ignored) */
    memset(&sigchld_action, 0, sizeof(sigchld_action));
    sigchld_action.sa_handler = sigchld_handler;
    if (sigaction(SIGCHLD, &sigchld_action, NULL) != 0) {
        fprintf(stderr, "Error setting SIGCHLD handler: %s\n", strerror(errno));
        return -1;
    }

    /* Temporarily block SIGCHLD signals */
    sigemptyset(&sigchld_sigset);
    sigaddset(&sigchld_sigset, SIGCHLD);
    if (sigprocmask(SIG_BLOCK, &sigchld_sigset, NULL) != 0) {
        fprintf(stderr, "Failed to block SIGCHLD: %s\n", strerror(errno));
        return -1;
    }

    /* Spawn a child process, which will send us the SIGCHLD signal when it
       exits---as we've blocked SIGCHLD this signal will be pending until the
       pselect() call below */
    if (fork() == 0) {
        puts("Child process is exiting");
        return 0;
    }

    /* Block on reading from STDIN, until the SIGCHLD signal interrupts us */
    FD_ZERO(&readfds);
    FD_SET(0, &readfds);

    /* Unblock all signals during pselect()'s execution */
    sigemptyset(&empty_sigset);

    puts("Waiting for Enter or signal...");
    psignal_result = pselect(1, &readfds, NULL, NULL, NULL, &empty_sigset);
    psignal_err = errno;

    printf("pselect() returned %d: %s (%d)\n", psignal_result,
        strerror(psignal_err), psignal_err);

    return 0;
}