Linux vfork()

转自：https://blog.csdn.net/jianchi88/article/details/6985326

1.vfork()创建子进程，在调用exec()之前或exit()之前，子进程与父进程共享数据段（与fork()不同，fork要拷贝父进程的数据段,堆栈段）

2.调用vfork()后，子进程先执行，父进程被挂起，直到子进程调用了exec或exit之后，父进程才执行。

例子1：

fork()

#include <unistd.h>
#include <stdio.h>

int main(int argc, char const *argv[])
{
	int cnt = 1;

	pid_t pid = fork();

	if(pid<0){
		printf("process error!!\n");
		return 1;
	}
	else if(pid==0){
		printf("this is a child process, id = %d, count =%d \n",getpid(),cnt++);
	}
	else
		printf("this is the parent process, id = %d, count =%d \n",getpid(),cnt++);

	return 0;
}

子进程拷贝父进程的数据段，堆栈段。处于不同的内存位置，所以cnt都是1

输出：

this is the parent process, id = 2661, count =1
this is a child process, id = 2664, count =1

例子2：

使用vfork(),但子进程不调用exit()或exec()，父进程一直挂起

导致死锁！

#include <unistd.h>
#include <stdio.h>

int main(int argc, char const *argv[])
{
	int cnt = 1;

	pid_t pid = vfork();

	if(pid<0){
		printf("process error!!\n");
		return 1;
	}
	else if(pid==0){
		printf("this is a child process, id = %d, count =%d \n",getpid(),cnt++);
	}
	else
		printf("this is the parent process, id = %d, count =%d \n",getpid(),cnt++);

	return 0;
}

输出：

this is a child process, id = 3248, count =1
this is the parent process, id = 3247, count =4195584
vfork: cxa_atexit.c:100: __new_exitfn: Assertion `l != NULL' failed.
已放弃 (核心已转储)

例子3：

使用vfork(),并且子进程调用exit()或exec()

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

int main(int argc, char const *argv[])
{
	int cnt = 1;

	pid_t pid = vfork();

	if(pid<0){
		printf("process error!!\n");
		return 1;
	}
	else if(pid==0){
		printf("this is a child process, id = %d, count =%d \n",getpid(),cnt++);
		exit(1);
	}
	else
		printf("this is the parent process, id = %d, count =%d \n",getpid(),cnt++);

	return 0;
}

子进程执行exit(1)退出后，父进程开始执行，由于共享数据段，所以cnt在子进程加1的基础上再加1 =2

this is a child process, id = 3497, count =1
this is the parent process, id = 3496, count =2

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