linux – 为什么我必须`wait()`用于子进程？

I’ll probably have to add a process table that stores the child pids
and have to use waitpid – not immideately,but after some time has
passed – which is a problem,because the running time of the children
varies from few microseconds to several minutes. If I use waitpid too
early,my parent process will get blocked

查看documentation for waitpid.您可以告诉waitpid不阻止(即,如果没有孩子可以立即返回)使用WNOHANG选项.而且,你不需要给waitpid一个PID.你可以指定-1,它会等待任何孩子.所以调用waitpid如下所示适合您的无阻塞约束和no-saving-pids约束：

waitpid( -1,&status,WNOHANG );

如果你真的不想正确地处理流程创建,那么你可以通过两次分享来获得init的收获责任,收获孩子,并给exec提交给孙子：

pid_t temp_pid,child_pid;
temp_pid = fork();
if( temp_pid == 0 ){
    child_pid = fork();
    if( child_pid == 0 ){
        // exec()
        error( EXIT_FAILURE,errno,"failed to exec :(" );
    } else if( child_pid < 0 ){
        error( EXIT_FAILURE,"failed to fork :(" );
    }
    exit( EXIT_SUCCESS );
} else if( temp_pid < 0 ){
    error( EXIT_FAILURE,"failed to fork :(" );
} else {
    wait( temp_pid );
}

在上述代码片段中,子进程分叉自己的子进程,立即存在,然后立即由父进程获取.孙子是孤儿,由init采用,将自动收回.

Why does Linux keep zombies at all? Why do I have to wait for my
children? Is this to enforce discipline on parent processes? In
decades of using Linux I have never got anything useful out of zombie
processes,I don’t quite get the usefulness of zombies as a “feature”.
If the answer is that parent processes need to have a way to find out
what happened to their children,then for god’s sake there is no
reason to count zombies as normal processes and forbid the creation of
non-zombie processes just because there are too many zombies.

你如何提出一个可以有效地检索进程的退出代码？问题是PID =退出代码(等)必须是一对一的.如果内核一旦退出,即可释放进程的PID,然后一个新的进程继承同一个PID并退出,那么你如何处理一个PID的两个代码？感兴趣的进程将如何检索第一个进程的退出代码？不要以为没有人关心退出代码.你认为是一个麻烦/ bug被广泛认为是有用和干净的.

On the system I’m currently developing for I can only spawn 400 to 500
processes before everything grinds to halt (it’s a badly maintained
CentOS system running on the cheapest VServer I could find – but still
400 zombies are less than a few kB of information)

关于使受到广泛接受的内核行为的一个替罪羊,显然是对维持不良/廉价系统的挫折显得不正确.

通常,您的最大进程数仅受您的内存限制.你可以看到你的极限：

cat /proc/sys/kernel/threads-max