waitpid()函数

waitpid函数

作用同于wait，但可指定pid进程清理，可以不阻塞。

pid_t waitpid(pid_t pid,int *status,int options);成功：返回清理掉的子进程ID；失败：-1（无子进程）

特殊参数和返回情况：

参数pid：

>0 回收指定ID的子进程

-1 回收任意子进程（相当于wait）

0 回收和当前调用waitpid一个组的所有子进程

< -1 回收指定进程组内的任意子进程

返回0：参数3为WNOHANG，且子进程正在运行。

注意：一次wait或waitpid调用只能清理一个子进程，清理多个子进程需要用到循环

/***
loop_wait.c
***/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>int main(int argc, char *argv[])
{int n = 5, i;                //默认创建5个子进程
    pid_t p, q;if(argc == 2){    n = atoi(argv[1]);}for(i = 0; i < n; i++)     {//出口1,父进程专用出口p = fork();if(p == 0) {break;            //出口2,子进程出口,i不自增} else if (i == 3){q = p;}}if(n == i){sleep(n);printf("I am parent, pid = %d\n", getpid(), getgid());//pid_t pid = waitpid(q, NULL, WNOHANG);
//        pid_t pid = wait(NULL);//printf("child pid = %d\n", pid);while(1);} else {sleep(i);printf("I'm %dth child, pid = %d, gpid=%d\n", i+1, getpid(), getgid());while(1);}return 0;
}

/***
waitpid.c
***/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>int main(void)
{pid_t pid, pid2, wpid;int flg = 0;pid = fork();pid2 = fork();if(pid == -1){perror("fork error");exit(1);} else if(pid == 0){        //sonprintf("I'm process child, pid = %d\n", getpid());sleep(5);                exit(4);} else {                    //parentdo {wpid = waitpid(pid, NULL, WNOHANG);//wpid = wait(NULL);printf("---wpid = %d--------%d\n", wpid, flg++);if(wpid == 0){printf("NO child exited\n");sleep(1);        }} while (wpid == 0);        //子进程不可回收if(wpid == pid){        //回收了指定子进程printf("I'm parent, I catched child process,""pid = %d\n", wpid);} else {printf("other...\n");}}return 0;
}

/***
waitpid2.c
***/
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>int main(void)
{pid_t pid, pid2, wpid;int flg = 0;pid = fork();pid2 = fork();if(pid == -1){perror("fork error");exit(1);} else if(pid == 0){        //sonprintf("I'm process child, pid = %d\n", getpid());sleep(5);                exit(4);} else {                    //parentdo {wpid = waitpid(pid, NULL, WNOHANG);//wpid = wait(NULL);printf("---wpid = %d--------%d\n", wpid, flg++);if(wpid == 0){printf("NO child exited\n");sleep(1);        }} while (wpid == 0);        //子进程不可回收if(wpid == pid){        //回收了指定子进程printf("I'm parent, I catched child process,""pid = %d\n", wpid);} else {printf("other...\n");}}return 0;
}

/***
waitpid3.c
***/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>int main(int argc, char *argv[])
{int n = 5, i;                
pid_t p, q;if(argc == 2){    n = atoi(argv[1]);}q = getpid();for(i = 0; i < n; i++)     {p = fork();if(p == 0) {break;            } }if(n == i){  // parent
        sleep(n);printf("I am parent, pid = %d\n", getpid());for (i = 0; i < n; i++) {p = waitpid(0, NULL, WNOHANG);printf("wait  pid = %d\n", p);}} else {sleep(i);printf("I'm %dth child, pid = %d\n", i+1, getpid());}return 0;
}