Unix环境高级编程--8-进程控制---8.7函数waitid 8.8函数wait3 wait4

1、Single Unix Specification支持一个取得进程终止状态的函数--waitid，此函数类似于waitpid：

       pid_t wait(int *status);

       pid_t waitpid(pid_t pid, int *status, int options);

       int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

2、wait3和wait4

       pid_t wait3(int *status, int options,struct rusage *rusage);

       pid_t wait4(pid_t pid, int *status, int options,struct rusage *rusage);
3、竞争条件

{pid_t pid;pid = fork();if(pid < 0){}else if(pid == 0)//一级子进程{pid = fork();{if(pid < 0){}else if(pid > 0)//一级子进程{exit(0);}//二级子进程，睡眠2秒后退出；也就是说二级子进程肯定会后面退出，变成孤儿进程sleep(2);printf("second child, parents");exit(0);}}if(waitpid(pid, NULL, 0) != pid){} //这个地方等待的pid算等待谁呢？？？？exit(0);    
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