Issue #5446 has been updated by Petr Chalupa.


We had to get around missing at_fork in concurrent-ruby as well. Since we are avoiding monkey_patching we had to result in lazy-checking pid, when it changes we re-create a resource. The resource has to check on every usage though which is not good.

Having Process.remove_at_fork(proc) is critical, an user of at_fork has to be able to unregister callback when the resource is not used any further.

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Feature #5446: at_fork callback API
https://bugs.ruby-lang.org/issues/5446#change-61344

* Author: Eric Wong
* Status: Assigned
* Priority: Normal
* Assignee: Motohiro KOSAKI
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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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