与父进程分离子进程 [英] Detach child process from parent

问题描述

当从父进程派生的子进程死亡时，它在某种程度上仍然存在，并处于僵尸状态，直到从wait()调用中获得该子进程为止.

When a child process forked from a parent dies, it still exists to some extent and is left in a zombie state, until it is reaped from a wait() call.

是否可以解除这种亲子关系，并让孩子自动获得收成?也许让孩子成为孩子的孤儿，或者其他什么事情?

Is is possible to detach this parent-child relationship and have the children be automatically reaped? Maybe orphan off the child to init, or something?

可能的用例:在一个长期存在的程序中创建大量的抛弃式"进程，而无需持有"越来越多的无法由操作系统回收的僵尸PID.

Possible use case: Creating a lot of fire-and-forget processes in a long-lived program, without "holding" on to an increasing list of zombie PIDs that cannot be recycled by the OS.

推荐答案

每 POSIX _exit()文档:

如果调用进程的父进程已设置其 SA_NOCLDWAIT标志或已将SIGCHLD信号的操作设置为 SIG_IGN:

If the parent process of the calling process has set its SA_NOCLDWAIT flag or has set the action for the SIGCHLD signal to SIG_IGN:

• 该进程的状态信息(请参阅状态信息)(如果有的话)应被丢弃.

• The process' status information (see Status Information), if any, shall be discarded.

调用过程的生存期将立即结束.如果设置了SA_NOCLDWAIT，则是否定义SIGCHLD由实现定义 信号发送到父进程.

The lifetime of the calling process shall end immediately. If SA_NOCLDWAIT is set, it is implementation-defined whether a SIGCHLD signal is sent to the parent process.

如果在wait()，waitpid()或waitid()中阻塞了调用进程的父进程中的线程，并且父进程具有 在等待的孩子集中，没有剩余的孩子进程， wait()，waitid()或waitpid()功能将失败并设置errno 到[ECHILD].

If a thread in the parent process of the calling process is blocked in wait(), waitpid(), or waitid(), and the parent process has no remaining child processes in the set of waited-for children, the wait(), waitid(), or waitpid() function shall fail and set errno to [ECHILD].

否则:

• 状态信息(请参阅状态信息)将生成.

• Status information (see Status Information) shall be generated.

应将呼叫过程转换为僵尸过程.其状态信息应提供给父进程 直到进程的生命周期结束.

The calling process shall be transformed into a zombie process. Its status information shall be made available to the parent process until the process' lifetime ends.

...

简而言之，为了防止子进程成为僵尸进程，最简单的方法是调用sigignore( SIGCHLD );

In short, to prevent child processes from becoming zombie processes, the simplest way is to call sigignore( SIGCHLD );

更新

那确实影响了等待任何子进程的能力，这可能是不希望的. setsid()库函数允许进程将自身与其父级解除关联:

That does impact the ability to wait for any child process, which may not be desired. The setsid() library function allows a process to disassociate itself from its parent:

pid_t child = fork();
if ( ( pid_t ) 0 == child )
{
    int rc = setsid();

    rc = execv(...);
}
else ...

解除关联的子进程不会在我安装的Solaris 11.2实例上创建僵尸，也不会发送SIGCHLD到父进程.

The disassociated child process doesn't create a zombie nor send SIGCHLD to the parent process on my installed instance of Solaris 11.2.

这是即发即弃"子进程的缩写守护进程，仅执行防止创建僵尸程序或将SIGCHLD发送给父进程的必要操作.有关更完整的守护程序，请参见 Linux守护程序

This is an abbreviated daemonization of a "fire-and-forget" child process, only doing what is necessary to prevent creating a zombie or sending SIGCHLD to the parent process. For a much fuller daemonization procedure, see Linux daemonize

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