子进程回收
回收子进程,知道子进程的死亡原因
作用:阻塞等待,回收子进程资源,查看死亡原因
pid_t wait(int *status);
status状态
返回值:成功返回终止的子进程ID,失败返回-1
子进程的死亡原因:
正常死亡WIFEXITED 如果WIFEXITED为真,使用WEXITSTATUS得到退出状态
非正常死亡WIFSIGNALED 如果WIFSIGNALED为真,使用WTERMSIG 得到信号
wait.c
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<stdlib.h>
int main(int argc,char *argv[])
{
pid_t pid=fork();
if(pid==0){
printf("I am child,will die\n");
sleep(2);
while(1){
printf("I am child\n");
sleep(1);
}
//return 101;
exit(102);
}
else if(pid>0){
printf("I am parent,wait for child die\n");
pid_t wpid=wait(NULL);
printf("wait ok,wpid=%d,pid=%d\n",wpid,pid);
if(WIFEXITED(status)){
printf("child exit with %d\n",WEXITSTATUS(status));
}
if(WIFSIGNALED(status)){
printf("child killed by %d\n",WTERMSIG(status));
}
while(1){
sleep(1);
}
}
return 0;
}
pid_t waitpid(pid_t pid,int *status,int options);
pid <-1 组id =-1回收任意 =0回收和调用进程组id相同组的子进程 >0回收指定ID options 0与wait相同,也会阻塞 WNOHANG如果当前没有子进程退出会立刻返回
返回值:如果设置了WNOHANG,如果没有子进程退出,返回0
如果有子进程退出,返回退出的pid
失败返回-1(没有子进程)
waitpid.c
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
int main(int argc,char *argv[])
{
pid_t pid=fork();
if(pid==0){
printf("I am child,pid=%d\n",getpid());
sleep(2);
}
else if(pid>0){
printf("I am parent,pid=%d\n",getpid());
int ret;
while(ret=waitpid(-1,NULL,WNOHANG)==0){
sleep(1)
}
printf("ret =%d\n",ret);
ret=waitpid(-1,NULL,WNOHANG);
if(ret<0){
perror("wait arr");
}
while(1){
sleep(1);
}
}
return 0;
}
用wait回收多个子进程
nfork_wait.c
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
int main(int argc,char *argv[])
{
int n=5;
int i=0;
pid_t pid;
for(i=0;i<5;i++){
pid=fork();
if(pid==0){
printf("I am child,pid=%d\n",getpid());
break;
}
}
sleep(i);
if(i==5){
for(i=0;i<5;i++){
pid_t wpid=wait(NULL);
printf("wpid=%d\n"wpid);
}
while(1){
sleep(1);
}
}
return 0;
}
用waitpid回收多个子进程
nfork_waitpid.c
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
int main(int argc,char *argv[])
{
int n=5;
int i=0;
pid_t pid;
for(i=0;i<5;i++){
pid=fork();
if(pid==0){
break;
}
}
sleep(i);
if(i==5){
printf("I am parent,pid=%d\n",getpid());
while(1){
pid_t wpid=waitpid(-1,NULL,WNONANG);
if(wpid==-1){
break;
}
else if(wpid>0){
printf("waitpid wpid=%d\n",wpid);
}
}
while(1){
sleep(1);
}
}
if(i<5){
//sleep(i);
printf("I am child,pid=%d\n",getpid());
}
return 0;
}