pipe io

#define _GNU_SOURCE
#define _POSIX_C_SOURCE 199309L

#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <unistd.h>
#include <time.h>

#define BILLION 1e9

int main(int argc, char *argv[]) {
    int pipefd_1[2];

    struct timespec start, stop;
    clockid_t clk_id = CLOCK_REALTIME;

    // for child and parent process run on the same cpu
    cpu_set_t set;
    int parentCPU, childCPU;

    char testChar = 'a';        /* Use for test */

    if (argc != 5) {
        fprintf(stderr, "Usage: %s parent-cpu child-cpu times\n",
                argv[0]);
        exit(EXIT_FAILURE);
    }

    parentCPU = atoi(argv[1]);
    childCPU = atoi(argv[2]);
    int const times  = atoi(argv[3]);
    int const writeEh  = atoi(argv[0]);

    CPU_ZERO(&set);

    if (pipe(pipefd_1) == -1) {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    char ch;
    switch (fork()) {
        case -1:    /* error */
            perror("fork");
            exit(EXIT_FAILURE);

        case 0:     /* child process */
            CPU_SET(childCPU, &set);

            if (sched_setaffinity(getpid(), sizeof(set), &set) == -1) {
                perror("set cpu for child process");
                exit(EXIT_FAILURE);
            }



            for (int i = 0; i < times; ++i) {
                if(!writeEh) write(pipefd_1[1], &ch, 1);
                else read(pipefd_1[0], &ch, 1);
            }

            exit(EXIT_SUCCESS);

        default:    /* parent process */
            CPU_SET(parentCPU, &set);

            if (sched_setaffinity(getpid(), sizeof(set), &set) == -1) {
                perror("set cpu for parent process");
                exit(EXIT_FAILURE);
            }


            if(0>clock_gettime(clk_id, &start)) return perror("clock_gettime"),1;
            for (int i = 0; i < times; ++i) {
                if(writeEh) write(pipefd_1[1], &ch, 1);
                else read(pipefd_1[0], &ch, 1);
            }
            if(0>clock_gettime(clk_id, &stop)) return perror("clock_gettime"),1;

            printf("the average cost of io is: %lf nsec\n", ((stop.tv_sec - start.tv_sec) * BILLION
                         + stop.tv_nsec - start.tv_nsec) / times);
    }

    exit(EXIT_SUCCESS);
}