Issue #5446 has been updated by Shyouhei Urabe.


We looked at this issue at today's developer meeting.

I was told that async-signal-safety is no longer the issue because in comment #4 the OP already restricted the request to fork method that runs ruby code. That's a good thing to know.

Then, given repeated request of this functionality, why not start this feature as a gem?  Because we focus on fork that runs ruby code, the needed functionality is doable in pure ruby I think.  Is there any reason this should be done by the language core (apart from monkey-paytching ugliness)?

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Feature #5446: at_fork callback API
https://bugs.ruby-lang.org/issues/5446#change-62193

* Author: Eric Wong
* Status: Assigned
* Priority: Normal
* Assignee: Motohiro KOSAKI
* Target version: 
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It would be good if Ruby provides an API for registering fork() handlers.

This allows libraries to automatically and agnostically reinitialize resources
such as open IO objects in child processes whenever fork() is called by a user
application.  Use of this API by library authors will reduce false/improper
sharing of objects across processes when interacting with other
libraries/applications that may fork.

This Ruby API should function similarly to pthread_atfork() which allows
(at least) three different callbacks to be registered:

1) prepare - called before fork() in the original process
2) parent - called after fork() in the original process
3) child - called after fork() in the child process

It should be possible to register multiple callbacks for each action
(like at_exit and pthread_atfork(3)).

These callbacks should be called whenever fork() is used:

- Kernel#fork
- IO.popen
- ``
- Kernel#system

... And any other APIs I've forgotten about

I also want to consider handlers that only need to be called for plain
fork() use (without immediate exec() afterwards, like with `` and system()).

Ruby already has the internal support for most of this this to manage mutexes,
Thread structures, and RNG seed.  Currently, no external API is exposed.  I can
prepare a patch if an API is decided upon.




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