waitpid()函數

waitpid函數

?作用同于wait，但可指定pid進程清理，可以不阻塞。

pid_t waitpid(pid_t pid,int *status,int options);成功：返回清理掉的子進程ID；失敗：-1（無子進程）

特殊參數和返回情況：

參數pid：

?????? >0 回收指定ID的子進程

?????? -1 回收任意子進程（相當于wait）

?????? 0 回收和當前調用waitpid一個組的所有子進程

?????? < -1 回收指定進程組內的任意子進程

返回0：參數3為WNOHANG，且子進程正在運行。

注意：一次wait或waitpid調用只能清理一個子進程，清理多個子進程需要用到循環

/***
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;                //默認創建5個子進程
    pid_t p, q;if(argc == 2){    n = atoi(argv[1]);}for(i = 0; i < n; i++)     {//出口1,父進程專用出口p = fork();if(p == 0) {break;            //出口2,子進程出口,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);        //子進程不可回收if(wpid == pid){        //回收了指定子進程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);        //子進程不可回收if(wpid == pid){        //回收了指定子進程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;
}

waitpid：

?????? 參1：??? pid ?> 0?????? 指定進程id回收

???????????????????? pid = -1 ?????? 回收任意子進程

???????????????????? pid = 0????????? 回收本組任意子進程

???????????????????? pid < -1 ?????? 回收該進程組的任意子進程

?????? 參2：??? status：

???????????????????? 返回：成功：pid? 失敗 -1

???????????????????? status：傳出參數

???????????????????? 1： 阻塞等待子進程

???????????????????? 2： 回收子進程資源

???????????????????? 3:??? 獲取子進程結束狀態：1）WIFEXITED（）真

????????????????????????????????????????????????????????????????????? WEXITSTATUS（）獲取子進程退出狀態

?????????????????????????????????????????????????????????????? 2）WIFSIGNALED（） 真

????????????????????????????????????????????????????????????????????? WTERMSIG（）獲取導致子進程終止的信號的?????????????????????????????????????????????????????????????????????????????????????????? 編碼

參3：??? 0 ：（wait）阻塞回收

????????????? WBNIOHANG：非阻塞回收（輪詢）

返回值：?????? 成功：pid? 失敗 -1? 返回 0 值： 參3傳WNOHANG，并且子進程尚未結束。