Feature #22444: Ractor.new should use Ractor.shareable_proc semantics for the block

• Status: Open
• Assignee: -
• Target version: -

[jhawthorn (John Hawthorn)]

#21557 introduced very well considered rules for Ractor.shareable_proc, where locals can be referenced so long as they are shareable and never reassigned. However Ractor.new { ... } continues to use a more restrictive rule that no local variable access is allowed at all.

I'd like to propose that Ractor.new follow the same rules as Ractor.shareable_proc. This simplifies implementation, and should be simpler for users both because of what it allows and because of consistency.

outer_var = :ok
Ractor.new { puts outer_var }.join # raise on 4.0, I propose we allow this
Ractor.new(outer_var) { |inner_var| puts inner_var }.join # old way to do this, still works

# This doesn't add any new abilities, as one could already emulate this with the following on 4.0
pr = Ractor.shareable_proc { puts outer_var } # allowed, because no reassignment to outer_var
Ractor.new(pr){ |pr| pr.call }.join # allowed, because pr is shareable

unshareable = Object.new
reassigned = :bad
Ractor.new { puts unshareable }.join # still raises because unshareable
Ractor.new { puts reassigned }.join # still raises due to reassignment
reassigned = :still_bad

self continues to be the new Ractor object.

One additional change here is that previously the proc passed to Ractor.new(&some_proc) would actually be mutated to be shareable. I don't think this was intentional and we should remove this behaviour.

[jhawthorn (John Hawthorn)]

• Description updated (diff)