标签：blog ar io 使用 for on 文件 2014 问题
先抄录网上一段对僵死进程的描述：如下测试：
[root@limt ~]# ps -ef|grep 16704 root 16704 16703 0 04:06 pts/1 00:00:00 [a.out] <defunct> root 16719 8866 0 04:06 pts/3 00:00:00 grep 16704 [root@limt ~]# [root@limt ~]# [root@limt ~]# kill -9 16704 [root@limt ~]# [root@limt ~]# ps -ef|grep 16704 root 16704 16703 0 04:06 pts/1 00:00:00 [a.out] <defunct> root 16725 8866 0 04:06 pts/3 00:00:00 grep 16704
从开发角度，有两种方法来避免僵死进程：
1 通过signal函数处理，因为每一个子进程退出都会向父进程发生一个SIGCHILD信号
2 通过fork两次子进程实现，使子进程的父进程为init进程（），大多数守护进程就是这样实现的
简单程序演示产生僵死进程的过程：
一 父进程fork一个子进程然后不使用waitpid函数，直接退出，而子进程sleep 120秒后退出
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
pid_t pid;
pid = fork();
if (pid == 0) {
int iPid = (int)getpid();
fprintf(stderr,"I am child,%d\n",iPid);
sleep(120);
fprintf(stderr, "Child exits\n");
return EXIT_SUCCESS;
}
int iPid = (int)getpid();
fprintf(stderr,"I am parent,%d\n",iPid);
fprintf(stderr, "parent exits\n");
return EXIT_SUCCESS;
}
[root@limt ~]# gcc Zom.c
[root@limt ~]# ./a.out
[root@limt ~]# ./a.out
I am parent,15019
parent exits
I am child,15020
从输出看父进程先退出，然后子进程运行sleep函数
[root@limt ~]# ps -ef|grep 15019 //查看父进程
root 15046 8866 0 03:29 pts/3 00:00:00 grep 15019
[root@limt ~]#
[root@limt ~]# ps -ef|grep 15020 //查看子进程
root 15020 1 0 03:29 pts/1 00:00:00 ./a.out
root 15056 8866 0 03:29 pts/3 00:00:00 grep 15020
从ps看父进程已经销毁，子进程的父进程号为1，也就是init进程
二 父进程fork一个子进程然后使用waitpid函数，然后退出，而子进程sleep 120秒后退出
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
pid_t pid;
pid = fork();
if (pid == 0) {
int iPid = (int)getpid();
fprintf(stderr,"I am child,%d\n",iPid);
sleep(120);
fprintf(stderr, "Child exits\n");
return EXIT_SUCCESS;
}
int iPid = (int)getpid();
fprintf(stderr,"I am parent,%d\n",iPid);
waitpid(pid,NULL,0);
fprintf(stderr, "parent exits\n");
return EXIT_SUCCESS;
}
[root@limt ~]# gcc Zom.c
[root@limt ~]# ./a.out
I am parent,15187
I am child,15188
Child exits
parent exits
从输出看子进程先退出，父进程一直等待子进程退出后才退出
[root@limt ~]# ps -ef|grep 15187 //查看父进程
root 15187 7459 0 03:32 pts/1 00:00:00 ./a.out
root 15188 15187 0 03:32 pts/1 00:00:00 ./a.out
root 15197 8866 0 03:33 pts/3 00:00:00 grep 15187
[root@limt ~]# ps -ef|grep 15188 //查看子进程
root 15188 15187 0 03:32 pts/1 00:00:00 ./a.out
root 15207 8866 0 03:33 pts/3 00:00:00 grep 15188
三 父进程fork一个子进程，然后使用waitpid函数，最后使用sleep函数，而子进程sleep 40秒后退出
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
pid_t pid;
pid = fork();
if (pid == 0) {
int iPid = (int)getpid();
fprintf(stderr,"I am child,%d\n",iPid);
sleep(40);
fprintf(stderr, "Child exits\n");
return EXIT_SUCCESS;
}
int iPid = (int)getpid();
fprintf(stderr,"I am parent,%d\n",iPid);
waitpid(pid,NULL,0);
fprintf(stderr, "sleep....\n");
sleep(120);
fprintf(stderr, "parent exits\n");
return EXIT_SUCCESS;
}
[root@limt ~]# ./a.out
I am parent,15673
I am child,15674
Child exits //等待40秒后输出
sleep.... //等待40秒后输出
parent exits
从上面的输出看sleep函数没有立刻执行，而是等待子进程运行完成才执行，实际是在等待waitpid函数返回
[root@limt ~]# ps -ef|grep 15673 //程序运行40秒内
root 15673 7459 0 03:43 pts/1 00:00:00 ./a.out
root 15674 15673 0 03:43 pts/1 00:00:00 ./a.out
root 15681 8866 0 03:44 pts/3 00:00:00 grep 15673
[root@limt ~]# ps -ef|grep 15674 //程序运行40秒内
root 15674 15673 0 03:43 pts/1 00:00:00 ./a.out
root 15692 8866 0 03:44 pts/3 00:00:00 grep 15674
[root@limt ~]#
[root@limt ~]# ps -ef|grep 15673 //程序运行40秒外
root 15673 7459 0 03:43 pts/1 00:00:00 ./a.out
root 15725 8866 0 03:44 pts/3 00:00:00 grep 15673
[root@limt ~]# ps -ef|grep 15674 //程序运行40秒外，子进程已经销毁
root 15727 8866 0 03:44 pts/3 00:00:00 grep 15674
[root@limt ~]#
[root@limt ~]# ps -ef|grep 15673 //程序运行120秒外
root 15798 8866 0 03:46 pts/3 00:00:00 grep 15673
四 父进程fork一个子进程，不使用waitpid函数然，而是sleep 120秒，而子进程sleep 1秒后退出
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
pid_t pid;
pid = fork();
if (pid == 0) {
int iPid = (int)getpid();
fprintf(stderr,"I am child,%d\n",iPid);
sleep(1);
fprintf(stderr, "Child exits\n");
return EXIT_SUCCESS;
}
int iPid = (int)getpid();
fprintf(stderr,"I am parent,%d\n",iPid);
fprintf(stderr, "sleep....\n");
sleep(120);
fprintf(stderr, "parent exits\n");
return EXIT_SUCCESS;
}
[root@limt ~]# ./a.out
I am parent,16026
sleep....
I am child,16027
Child exits
parent exits
从上面输出看子进程先于父进程退出
[root@limt ~]# ps -ef|grep 16026 //查看父进程
root 16026 7459 0 03:51 pts/1 00:00:00 ./a.out
root 16027 16026 0 03:51 pts/1 00:00:00 [a.out] <defunct>
root 16039 8866 0 03:51 pts/3 00:00:00 grep 16026
[root@limt ~]#
[root@limt ~]# ps -ef|grep 16027 //查看子进程，子进程处于僵死状态
root 16027 16026 0 03:51 pts/1 00:00:00 [a.out] <defunct>
root 16046 8866 0 03:51 pts/3 00:00:00 grep 16027
[root@limt ~]# top //top 进程显示存在一个僵死进程
top - 04:02:20 up 2:46, 4 users, load average: 0.21, 0.15, 0.15
Tasks: 280 total, 1 running, 278 sleeping, 0 stopped, 1 zombie
Cpu(s): 1.2%us, 0.6%sy, 0.0%ni, 97.4%id, 0.7%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 2050752k total, 1819480k used, 231272k free, 141876k buffers
Swap: 6291448k total, 0k used, 6291448k free, 775368k cached
[root@limt ~]# ps -ef|grep 16027 //120秒后僵死进程消失
root 16513 8866 0 04:01 pts/3 00:00:00 grep 16027
标签：blog ar io 使用 for on 文件 2014 问题
原文地址：http://blog.csdn.net/lmt818583/article/details/41980875
