multiprocessing_write.c

/*
   rm -f /tmp/out.txt && gcc cwrite.c && ./a.out $BUFSIZE $LINELEN --fbf  && cat out.txt | while read l; do echo ${#l}; done | sort -u
   */

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

void recode(char*, int, int);

int
main(int argc, char *argv[]) {
    int buf_size = atoi(argv[1]);
    int line_len = atoi(argv[2]);
    int buf_mode;
    if (strcmp(argv[3], "--nbf") == 0) {
        buf_mode = _IONBF;
    } else if (strcmp(argv[3], "--lbf") == 0) {
        buf_mode = _IOLBF;
    } else if (strcmp(argv[3], "--fbf") == 0) {
        buf_mode = _IOFBF;
    } else {
        printf("input buf mode!");
        _exit(1);
    }

    int j;
    char line[line_len];
    for (j=0; j<(line_len-1); j++) line[j] = 'x';
    line[j++] = '\n';
    line[j++] = '\0';

    for (int i=0; i<10; i++) {
        if (fork() == 0) {
            recode(line, buf_mode, buf_size);
            _exit(0);
        } else {
            continue;
        }
    }
    for (int i=0; i<10; i++) {
        wait(NULL);
    }
}

void
recode(char *line, int buf_size, int buf_mode) {
    FILE *out;
    char buf[buf_size];

    out = fopen("./out.txt", "a");
    setvbuf(out, buf, buf_mode, buf_size);
    for (int i=0; i<1000; i++) {
        fputs(line, out);
    }
    fclose(out);
}