freezing procs

ractor_shenanigans.rb

# frozen_string_literal: true
# requires ruby 3.1+

# Ractor.make_shareable(proc) only succeeds if everything on the proc's binding is shareable.
#
# This makes it difficult to create wrappers around Ractor.new that accept an arbitrary block.
# Even this would still require the block declare any outer variables as block-locals, even if
# they aren't used.
class ProcFreezer
  def initialize = freeze
  def call(&); Ractor.current.instance_exec(&) => Proc => p; p end # block must return a Proc
  def make_shareable(&) = Ractor.make_shareable(call(&))
  def self.ractor(*a, name: nil, &b)
    f = new
    b = f.make_shareable(&b)
    i = f.make_shareable {->(a;name){ puts "inner? => %p" % [Ractor.current]; b.call(*a) }}
    r = Ractor.new(a, i, name: name) do |a, i|
      puts "init Ractor => %p" % Ractor.current
      i.call(a)
    end
  end
end

ProcFreezer
  .ractor do puts "make_shareable => %p" % [Ractor.current]; -> {:bar} end
  .take
# >> make_shareable => #<Ractor:#1 running>
# >> init Ractor => #<Ractor:#11 (irb):218 running>                                                                 
# >> inner? => #<Ractor:#11 (irb):218 running>                                                                      
# => :bar

This solves a problem I'd been having: how to create a wrapper around Ractor.new. I want to initialize a ractor with some context vars, Tracepoint, etc, that the caller might not know or care about. Even if everthing is ractor sharable, it's still not trivial to fully isolate their proc.

I could probably remove some of the code here, but this was the first version I got working, so here it is. :)

honestly though, I'm probably better off just using fiddle to FFI-cheat with rb_isolate_proc_bang