Issue #5446 has been updated by Eregon (Benoit Daloze).


> Is there a way to expose Ruby methods/procs as C function pointers with JIT?

@normalperson That feels very hacky to me.
JIT'ing a function which is only called once seems suboptimal (and difficult to do before it's even called once).
Also some Ruby state likely needs to be restored before running any `after_fork` hook.

@byroot I agree, we should at least have `after_fork` (or `at_fork(when, &block)`).

Honestly I don't understand why we don't have this yet, it's obviously needed and every forking webserver out there ends up having its own hook.

For the use-case of purposefully keeping a database connection (which seems extremely rare), maybe one can require the database library with a different path to be explicit that playing with database fd sharing fire is wanted? (or some other mechanism so the `at_fork` hook is not installed in that case).

For the vast majority of fork uses in practice it would be much safer if database connections and other fds which are unsafe to keep open across forks were automatically closed.

And BTW the current workaround of checking pid is slower also on platforms not supporting `fork`, so it is inefficient for all platforms and webservers.

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Feature #5446: at_fork callback API
https://bugs.ruby-lang.org/issues/5446#change-91277

* Author: normalperson (Eric Wong)
* Status: Assigned
* Priority: Normal
* Assignee: kosaki (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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