僵尸进程的父进程终止后会发生什么? [英] What happens after the parent of zombie process terminates?

问题描述

我很好奇，僵尸进程会发生什么，如果它的父母不在乎等待它的话.

I'm just curious, what happens to zombie process, if it's parent doesn't care to wait for it.

假设我们有一个父母和一个孩子.孩子先于父母终止.

Suppose, we've a parent and a child. Child terminates before parent does.

从APUE:

内核为每个终止进程保留少量信息...至少
此信息包括进程ID，进程的终止状态....

The kernel keeps a small amount of information for every terminating process...Minimally
this information consists of the process ID, the termination status of the process....

需要父母使用waitpid()获取此信息.
但是，如果父母不等孩子就退出了，那会发生什么:

Parent is required to fetch this information using waitpid().
But if, parent exits without waiting for child, what happens:

内核是否删除此信息(肯定没有用)?
还是不断收集这些垃圾?
此实现特定吗?
或者，有没有一种标准的方法来处理这种情况?

Does the kernel delete this information (certainly it's of no use)?
Or, it keeps collecting this junk?
Is this implementation specific?
Or, is there a standard way to deal with this situation?

推荐答案

init自动采用孤立进程，该进程具有标准的SIGCHLD处理程序，该处理程序仅丢弃无效进程的退出状态.

Orphan processes are automatically adopted by init which has a standard SIGCHLD handler that just discards any exit status of a dead process.

在您的情况下，如果僵尸进程的父进程死亡，则僵尸孤儿将被init接受并清理.

In your case if the parent of a zombie process dies the zombie orphan will be adopted by init and cleaned up.

以下代码对此进行了测试:

The following code tests this:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>


int main() {
    pid_t child_pid;
    if (child_pid = fork()) { // fork a child, child will exit straight away
        char name[128];
        sprintf(name, "/proc/%d/stat", child_pid);
        char line[2048];

        // read childs /proc/pid/stat, field 3 will give its status
        FILE * fp = fopen(name, "r");

        while (fgets(line, sizeof(line), fp))
            puts(line);

        fclose(fp);

        usleep(5000000);

        // by now the child will have exited for sure, repeat
        fp = fopen(name, "r");

        while (fgets(line, sizeof(line), fp))
            puts(line);

        fclose(fp);

        // make another child to repeat the process and exit the parent
        if (!fork()) {
            usleep(5000000);
            // both parent and child will have exited by now

            fp = fopen(name, "r");

            // this should fail because init has already cleaned up the child
            if (!fp) {
                perror("fopen");
                return -1;
            }

            while (fgets(line, sizeof(line), fp))
                puts(line);

            fclose(fp);
        }

    }

    return 0;
}

这篇关于僵尸进程的父进程终止后会发生什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！