macos_fifo.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <fcntl.h>
#include <errno.h>

void sighandler(int sig) { };

int main(int argc, char **argv) {
    char *fifoname = tmpnam(NULL);
    int r = mkfifo(fifoname, 0);
    if (r == -1) {
        perror("mkfifo");
        exit(1);
    }
    printf("fifo: %s\n", fifoname);
    chmod(fifoname, 0777);

    sigset_t usr1set;
    sigemptyset(&usr1set);
    sigaddset(&usr1set, SIGUSR1);
    sigprocmask(SIG_BLOCK, &usr1set, NULL);

    pid_t pid = fork();
    if (pid == -1) {
        perror("fork");
        exit(1);
    }
    if (pid == 0) {
        /* child */
        void *s = signal(SIGUSR1, sighandler);
        if (s == SIG_ERR) {
            perror("signal (child)");
            exit(1);
        }
        printf("opening (child)\n");
        sigprocmask(SIG_UNBLOCK, &usr1set, NULL);
        int fd;
        while ((fd = open(fifoname, O_RDONLY)) == -1) {
            if (errno != EINTR) {
                perror("open (child)");
                exit(1);
            }
            printf("EINTR on open\n");
        }
        printf("opened fd %d\n", fd);
        char buf[3];
readagain:
        r = read(fd, buf, 2);
        if (r == -1) {
            if (errno == EINTR) {
                goto readagain;
            }
            perror("read (child)");
            exit(1);
        }
        buf[2] = '\0';
        printf("%s\n", buf);
        exit(0);
    } else {
        printf("parent\n");
        signal(SIGPIPE, SIG_IGN);
        for (int i = 0; i < 3; i++) {
            struct timespec tm;
            tm.tv_sec = 0;
            tm.tv_nsec = 1000000000;
            nanosleep(&tm, NULL);
            kill(pid, SIGUSR1);
        }
        int fd = open(fifoname, O_WRONLY);
        if (fd == -1) {
            perror("open (parnet)");
            exit(1);
        }
        char buf[3] = "gg";
        printf("parent writing to fd %d\n", fd);
        r = write(fd, buf, 2);
        if (r == -1) {
            perror("write (parent)");
            exit(1);
        }
        printf("exiting ok from parent\n");
        exit(0);
    }

}