Feature #18137: A new method to check Proc is isolated or not

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

[tagomoris (Satoshi Tagomori)]

I want to check a Proc is isolated or not, like Proc#isolated?.

Proc objects are passed to libraries very often. For example, Rack web application is a callable (respond_to(:call)) object, and it may be a Proc.
When the library will call that Proc object in a Ractor, the passed Proc should be isolated by Ractor.make_shareable(). Otherwise, it causes RuntimeError.

So I want to check the Proc object is isolated or not earlier. It should be very helpful for library users because of the early and clear error messages.

[ko1 (Koichi Sasada)]

Ractor.shareable?(proc_object) is not enough?

[ko1 (Koichi Sasada)]

I'm afraid that we can define "Isolated Proc".

As I know there are several versions.

1. self
   a: self is shareable
   b: self is not shareable

2. reference to outer scope variables
   x: no references
   y: has references, but read-only and values are fixed (if outer-scope variables are modified by other code, but keep to refer original values).
   z: has references, but the variable storage is independent from outer-scope.

example of y:

i = 1
pr = proc{
  p i #=> always 1
}
i = 2
pr.call #=> 1

example of z:

i = 1
pr = proc{
  p i += 1
}
i += 10
pr.call #=> 2

---

From Ractor perspective, x and y are acceptable. for a and b,
Ractor doesn't care because the self will be replaced with Ractor.new{} and define_method. Proc#call is not allowed (!! Now it is allowed. BUG!! https://bugs.ruby-lang.org/issues/18243).