hello/timethem.c

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>


#define N 5

typedef struct {
    double time;
    size_t nread;
} resultT;

int cmptime(const void *a, const void *b) {
    const resultT *aa = a, *bb = b;
    if (aa->time < bb->time) {
        return -1;
    } else if (aa->time > bb->time) {
        return +1;
    } else {
        return 0;
    }
}


resultT median (resultT *v, int n) {
    // n is small, keep it simple
    qsort(v, n, sizeof(*v), cmptime);
    return v[n / 2];

}


int main(int argc, char **argv) {
    resultT **results = calloc(sizeof(*results), argc);
    assert(results);
    for (int i = 1; i < argc; i++) {
        results[i] = calloc(sizeof(**results), N);
        assert(results[i]);
    }

    for (int j = 0; j < N; j++) {
        for (int i = 1; i < argc; i++) {
            struct timespec t0, t1;
            clock_gettime(CLOCK_MONOTONIC, &t0);
            size_t nread = 0;

            int out[2];
            if (pipe(out) == -1) {
                printf("%s: cannot create pipe: %s\n", argv[0], strerror(errno));
                exit(1);
            }

            pid_t pid = fork();
            switch(pid) {
                case -1:
                    fprintf(stderr, "%s: cannot fork: %s\n", argv[0], strerror(errno));
                    exit(1);
                case 0:
                    dup2(out[1], 1);
                    // close(out[0]);
                    // close(out[1]);
                    execl(argv[i], argv[i], (char *)NULL);
                    fprintf(stderr, "%s: cannot exec %s: %s\n", argv[0], argv[i], strerror(errno));
                    exit(1);
                default: {
                    close(out[1]);
                    ssize_t n;
                    char buf[16];
                    while ((n = read(out[0], buf, sizeof(buf))) > 0) {
                        nread += n;
                    }
                    int status;
                    while (waitpid(pid, &status, 0) != pid);
                }
            }
            clock_gettime(CLOCK_MONOTONIC, &t1);
            results[i][j].time = (t1.tv_sec - t0.tv_sec) * 1E9 + (t1.tv_nsec - t0.tv_nsec);
            results[i][j].nread = nread;
            fprintf(stderr, "%s: %s completed in %f ns\n", argv[0], argv[i], results[i][j].time);
        }
    }
    for (int i = 1; i < argc; i++) {
        resultT m = median(results[i], N);
        printf("%-20s %8.3f ms %2zd bytes\n", argv[i], m.time / 1E6, m.nread);
    }
    return 0;
}