Feature #5446


at_fork callback API

Added by normalperson (Eric Wong) about 10 years ago. Updated 6 months ago.

Target version:


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.

Related issues

Related to Ruby master - Bug #14009: macOS High Sierra and “fork” compatibilityClosedActions
Related to Ruby master - Feature #17795: Around `Process.fork` callbacks APIOpenActions

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