[ruby-core:58175] [ruby-trunk - Feature #5446] at_fork callback API

Issue #5446 has been updated by sam.saffron (Sam Saffron).


This is a critical feature for Ruby imho, at the moment there are 100 mechanisms for at_fork, we need a clean, supported ordered one. 

I think there should be strong parity with at_exit, so am not particularly fond of the symbol param. I would like. 

at_fork{ } # returns proc, a stack of procs that are called in order just before fork
after_fork {} # returns a proc, a stack of procs that are called in order just after child process launches 

The prepare thing for me seems like overkill. It would be like we are implementing 2 queues, one urgent, one less urgent. I don't really see the point. 

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There is a question of cancelling forks (eg: what happens when an exception is thrown during these callbacks?) 
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Feature #5446: at_fork callback API
https://bugs.ruby-lang.org/issues/5446#change-42762

Author: normalperson (Eric Wong)
Status: Assigned
Priority: Low
Assignee: kosaki (Motohiro KOSAKI)
Category: 
Target version: next minor


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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