ex11-01.c

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>


#define MSGSIZE 100

int main() {

    pid_t pid1, pid2;
    int filedes, p1[2], p2[2];
    fd_set initset, newset;
    int nread;
    char msg[MSGSIZE];
    pipe(p1);
    pipe(p2);
    pid1 = pid2 = 0;
    pid1 = fork();
    if (pid1 > 0)
        pid2 = fork();

    if (pid1 > 0 && pid2 > 0) {
        printf("[parent] hello!\n");
        close(p1[1]);
        close(p2[1]);
        FD_ZERO(&initset);
        FD_SET(p1[0], &initset);
        FD_SET(p2[0], &initset);
        newset = initset;
        while (select(p2[0] + 1, &newset, NULL, NULL, NULL) > 0) {
            if (FD_ISSET(p1[0], &newset))
                if (read(p1[0], msg, MSGSIZE) > 0) printf("[parent] %s\n", msg);
            if (FD_ISSET(p2[0], &newset))
                if (read(p2[0], msg, MSGSIZE) > 0)
                    printf("[parent] %s\n", msg);
            newset = initset;
        }
    } else if (pid1 == 0 && pid2 == 0) {
        printf("[fork1] hello!\n");
        close(p1[0]);
        close(p2[0]);
        close(p2[1]);
        dup2(p1[1], 1);
        execl("ex11-01c", "ex11-01c", (char *) 0);
    } else if (pid1 > 0 && pid2 == 0) {
        printf("[fork2] hello!\n");
        close(p1[0]);
        close(p1[1]);
        close(p2[0]);
        write(p2[1], "from fork2 via pipe", MSGSIZE);
        mkfifo("./fifo", 0666);
        filedes = open("./fifo", O_RDWR);
        nread = read(filedes, msg, MSGSIZE);
        printf("%s (%d)\n", msg, nread);
        close(filedes);
        unlink("./fifo");
    } else exit(1);
}