Bug #21505: [Ractor] calling exit from non-main ractor will hang if main ractor waits on it

• Status: Closed
• Assignee: ractor
• Target version: -
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[luke-gru (Luke Gruber)]

r = Ractor.new do
  exit
end

r.join # hangs

Should exit be allowed in ractors? It would be easiest to disallow, as the code might be tricky if we allow it.

[Eregon (Benoit Daloze)]

Kernel#exit is basically just raise SystemExit, does it mean any exception in a Ractor hangs?
IOW, I don't think it should be disallowed because exit is just an Exception.

[luke-gru (Luke Gruber)]

Yeah fair enough. It's probably not as complicated to fix as I initially thought.

[jhawthorn (John Hawthorn)]

I opened https://github.com/ruby/ruby/pull/13838 which fixes this

./miniruby -e 'Ractor.new { exit }.join'
-e:1: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
-e:1:in 'Ractor#join': thrown by remote Ractor. (Ractor::RemoteError)
        from -e:1:in '<main>'
-e:1:in 'Kernel#exit': exit (SystemExit)
        from -e:1:in 'block in <main>'

In this PR we end up wrapping SystemExit in a Ractor::RemoteError rather than exiting the program. I don't know if that's the most desirable behaviour (versus translating back to SystemExit), but it makes sense to me as calling exit in a Ractor is a bit strange.

[jhawthorn (John Hawthorn)]

• Status changed from Open to Closed

Applied in changeset git|6c66458070e2de45213f473ac30b431ebea81b9b.

---

Fix rb_eSystemExit raised in Ractor

[Bug #21505]

Previously Ractor.new { exit }.join would hang because SystemExit was
special cased.

This commit updates this to take the same path as other exceptions,
which wraps the exception in a Ractor::RemoteError and does not end up
exiting the main Ractor. I don't know if that's what this should do, but
I think it's a reasonable behaviour as calling exit() in a Ractor is
odd.

in 'Ractor#join': thrown by remote Ractor. (Ractor::RemoteError)
   from -e:1:in '<main>'
in 'Kernel#exit': exit (SystemExit)
        from -e:1:in 'block in <main>'