[ruby-core:58195] [ruby-trunk - Feature #5446] at_fork callback API

Issue #5446 has been updated by jasonrclark (Jason Clark).


I'd love to see this added. Gems using threads (like newrelic_rpm) have a lot of potential for deadlocks when forking happens. This would gives a nice mechanism for dealing with those issues more generally, rather than having to hook things gem-by-gem like we do today.

New Relic + Resque has seen a lot of these types of problems, some of which are documented at https://github.com/resque/resque/issues/1101. While Resque has gem-specific hooks we lean on, having those hooks be at the Ruby level instead would be awesome.

Is there any possibility of this type of after_fork hook could also apply to daemonizing with Process.daemon? While we have fewer deadlocks, we often lose visibility after processes daemonize because we don't know to start our threads back up in the daemonized process. (See https://github.com/puma/puma/issues/335 for an example with the Puma web server).
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Feature #5446: at_fork callback API
https://bugs.ruby-lang.org/issues/5446#change-42778

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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