fork && clone @ Linux Kernel

除了用 fork 的方式來實現多線程的方式外,也可以用 clone 的方式.兩者最大的差別是在 Parent copy or not, fork 會copy Parent 的 space, 而 clone 卻是和 Parent 共用 space, 前者比較多用於對外的多平行執行序如external server/client,後者比較多用於 internal的 Process 如 mm management. fork_smp.c 可發現 Parent 的 data 不會被 Child 改變.

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

int main(int argc,char *argv[]) {
        int count = 1;
        int child;

        if(!(child = vfork())) {
                printf("This is son, his count is: %d. and his pid is: %d\n", ++count, getpid());
        } else {
                printf("This is father, his count is: %d, his pid is: %d\n", count, getpid());
        }
return 0;
}

clone.c 發現 Parent 的 Data 會被 Child 而改變.

#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <signal.h>
#define FIBER_STACK 8192

int a;
void * stack;
int do_something(){
        printf("This is son, the pid is:%d, the a is: %d\n", getpid(), ++a);
        free(stack);
        exit(1);
}
int main() {
        void * stack;
        a = 1;
        stack = malloc(FIBER_STACK);
        if(!stack) {
                printf("The stack failed\n");
                exit(0);
        }

        printf("creating son thread!!!\n");

        clone(&do_something, (char *)stack + FIBER_STACK, CLONE_VM|CLONE_VFORK, 0);
         printf("This is father, my pid is: %d, the a is: %d\n", getpid(), a);
         exit(1);
}

Refs: fork,vfork和clone底层实现 fork, vfork, clone,pthread_create,kernel_thread clone fork及vfork的区别