fork_test.c

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#include <sys/time.h>
#include <sys/wait.h>
#include <unistd.h>
#include <spawn.h>


#define FORK_TIME 1024

pid_t fspawn(const char* program){
    pid_t child_pid;

    child_pid = fork();

    if( child_pid == 0 ){
        // child
        execlp(program, program, NULL);
        perror("exec() error");
    }
    else if( child_pid > 0 ){
        // parent
        return child_pid;
    }
    else{
        perror("fork() error");
        exit(1);
    }
}

pid_t pspawn(const char* program, bool is_vfork){
    pid_t child_pid = -1;
    int ret;

    char** argv = NULL;
    argv = malloc(sizeof(char*) * 2);
    argv[0] = program;
    argv[1] = NULL;

    posix_spawnattr_t attr;
    posix_spawnattr_init(&attr);

    int flag = 0;
    if( is_vfork ){
        flag |= POSIX_SPAWN_USEVFORK;
        posix_spawnattr_setflags(&attr, flag);
    }

    ret = posix_spawnp(&child_pid, program, &attr, NULL, argv, NULL);

    if( ret != 0 && child_pid == -1 ){
        perror("fork() error");
        exit(1);
    }
    else if( ret != 0 ){
        fprintf(stderr, "pre-exec or exec() error");
        exit(1);
    }

    return child_pid;
}

int main(int argc, char *argv[]){
    pid_t child_pid;

    struct timeval start_time, finish_time, running_time;

    // fork-exec
    printf("fork-exec\n");
    gettimeofday(&start_time, NULL);
    for( int i = 0; i < FORK_TIME; i++ ){
        child_pid = fspawn("true");
        wait(NULL);
    }
    gettimeofday(&finish_time, NULL);
    timersub(&finish_time, &start_time, &running_time);

    printf("running time: %ld sec, %ld usec\n", running_time.tv_sec, running_time.tv_usec);
    
    // pspawn
    printf("pspawn\n");
    gettimeofday(&start_time, NULL);
    for( int i = 0; i < FORK_TIME; i++ ){
        child_pid = pspawn("true", false);
        if( child_pid != -1 ){
            wait(NULL);
        }
    }
    gettimeofday(&finish_time, NULL);
    timersub(&finish_time, &start_time, &running_time);

    printf("running time: %ld sec, %ld usec\n", running_time.tv_sec, running_time.tv_usec);

    // pspawn
    printf("pspawn vfork\n");
    gettimeofday(&start_time, NULL);
    for( int i = 0; i < FORK_TIME; i++ ){
        child_pid = pspawn("true", true);
        if( child_pid != -1 ){
            wait(NULL);
        }
    }
    gettimeofday(&finish_time, NULL);
    timersub(&finish_time, &start_time, &running_time);

    printf("running time: %ld sec, %ld usec\n", running_time.tv_sec, running_time.tv_usec);
    return 0;
}