[ruby-core:101253] [Ruby master Bug#17369] Introduce non-blocking `Process.wait`, `Kernel.system` and related methods.

Issue #17369 has been updated by ioquatix (Samuel Williams).


> Does such code still work, with a scheduler?

Yes.

> It sounds like you would need a way to set $? on the current Thread.

Nope, it's handled by `Process.wait` and so on.

> Otherwise, just switching between Fibers (e.g., on IO) would expose the $? of other Fibers, which will lead to bugs.

Agree, but we can't change this without potentially breaking existing code.

Also, is it okay that `Process.last_status` and `Process.last_status=` (hypothetical) are fiber local? Because Matz already said he was against class attributes that are actually fiber local (even if I agree in theory, excluding the fact that this is a breaking change).

> I expect that change to cause extremely few compatibility issues ($~, etc are already fiber-local + frame-local).

Great, if Matz can approve the change, then we can implement it, but it's separate from this PR, since this PR just makes the existing interface non-blocking.

----------------------------------------
Bug #17369: Introduce non-blocking `Process.wait`, `Kernel.system` and related methods.
https://bugs.ruby-lang.org/issues/17369#change-88930

* Author: ioquatix (Samuel Williams)
* Status: Assigned
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
https://github.com/ruby/ruby/pull/3852

This PR introduces optional hooks to the scheduler interface for handling `Process.wait`, `Kernel.system` and other related methods (`waitpid`, `wait2`, etc).

It funnels all methods through a new interface `Process::Status.wait` which is almost identical to `Process.wait` except for several key differences:

- The return value is a single instance of `Process::Status`.
- It does not set thread local `$?`.

This is necessary for keeping the scheduler interface simple (and side effects are generally bad anyway).



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