waitpid非阻塞时的用法
2016-02-29 23:26
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我们用这个程序和输出结果分析一下waitpid的用法和特点。我们将waitpid设置成WNOHANG非阻塞父进程状态;
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
pid_t pid, wpid;
int stat;
wpid = waitpid(-1, &stat, WNOHANG);
printf("first-pid: %d\n", wpid);
pid=fork();
if(pid < 0)
printf("error occurred!\n");
if(pid == 0)
{
printf("child\n");
sleep(5);
exit(0);
}
printf("parent\n");
wpid = waitpid(-1, &stat, WNOHANG);
printf("second-pid: %d\n", wpid);
sleep(7);
wpid = waitpid(-1, &stat, WNOHANG);
printf("third-pid: %d\n", wpid);
exit(0);
}
运行结果:
local@ubuntu:~/Practice/IPC/fork$ ./a.out
first-pid: -1
parent
second-pid: 0
child
third-pid: 3170
local@ubuntu:~/Practice/IPC/fork$
第一次调用waitpid时:此时尚未有子进程,所以waitpid出错,返回-1;
第二次调用waitpid时:此时有子进程,但子进程尚未结束,由于waitpid设置为非阻塞的,所以waitpid返回0;
第三次调用waitpid时:此时有子进程,所以waitpid返回子进程id;
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
pid_t pid, wpid;
int stat;
wpid = waitpid(-1, &stat, WNOHANG);
printf("first-pid: %d\n", wpid);
pid=fork();
if(pid < 0)
printf("error occurred!\n");
if(pid == 0)
{
printf("child\n");
sleep(5);
exit(0);
}
printf("parent\n");
wpid = waitpid(-1, &stat, WNOHANG);
printf("second-pid: %d\n", wpid);
sleep(7);
wpid = waitpid(-1, &stat, WNOHANG);
printf("third-pid: %d\n", wpid);
exit(0);
}
运行结果:
local@ubuntu:~/Practice/IPC/fork$ ./a.out
first-pid: -1
parent
second-pid: 0
child
third-pid: 3170
local@ubuntu:~/Practice/IPC/fork$
第一次调用waitpid时:此时尚未有子进程,所以waitpid出错,返回-1;
第二次调用waitpid时:此时有子进程,但子进程尚未结束,由于waitpid设置为非阻塞的,所以waitpid返回0;
第三次调用waitpid时:此时有子进程,所以waitpid返回子进程id;
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