fork 产生一个空的子进程
fork 产生一个空的子进程
调用exec函数簇，清除fork后子进程所有的东西，包括数据区，bbs区，堆区，栈区，代码区，甚至文件描述符和文件指针，成为真正意义的空子进程。利用"写时拷贝（copy-on-write）"技术.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
pid_t child_t = 0;
int val = 1234;
int main(int argc, const char *argv[])
{
FILE* fp = fopen("1.txt","w+");
/*
////////////////这段表示不继承进system()进程。/////////////////////////////////////
int fd = fileno(fp);
int flags = fcntl(fd, F_GETFD);
flags |= FD_CLOEXEC;
fcntl(fd, F_SETFD, flags);
//////////相当于open函数，其中flags参数可以传入O_CLOEXEC标记 [注意：linux 2.6.23才开始支持此标记]/////////////////////
*/
printf("start.......\n");
child_t = fork();
printf("child_t = %d\n",child_t);
sleep(3);
if(child_t < 0)
{
printf("fork error !\n");
}
else if(child_t == 0)
{
printf("child progam!\n");
if(execl("/bin/echo", "", "", NULL)<0) //调用exec函数库成为空子进程
perror("Err on execl");
sleep(30);
system("lsof | grep /work/test/small_test/1.txt");
printf("--------------------\n");
char iTest = 'a';
int ret = 0;
if((ret = fwrite(&iTest,sizeof(char),1,fp)) != sizeof(char))
{
printf("fwrite error %d\n",ret);
}
system("lsof | grep /work/test/small_test/1.txt");
printf("--------------------\n");
sleep(5);
system("lsof | grep /work/test/small_test/1.txt");
printf("--------------------\n");
}
else
{
printf("parent progam,child ID is %d\n",child_t);
system("lsof | grep /work/test/small_test/1.txt");
printf("--------------------\n");
fclose(fp);
system("lsof | grep /work/test/small_test/1.txt");
printf("--------------------\n");
sleep(60);
}
return 0;
}
打印信息
[user:small_test] ./test.i386.elf
start.......
child_t = 8244
child_t = 0
parent progam,child ID is 8244
child progam!
test.i386 8243 user 10u REG 8,17 0 2359313 /work/test/small_test/1.txt
sh 8246 user 10u REG 8,17 0 2359313 /work/test/small_test/1.txt
grep 8248 user 10u REG 8,17 0 2359313 /work/test/small_test/1.txt
--------------------
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