Fix Ractor IsolationError with file and thread safety enabled

[bkuhlmann]

Why

Hello. 👋 With the release of Version 0.2.0, especially this commit, you'll now get a Ractor::IsolationError when writing data.

How

Here's the quickest way I could reproduce this:

#! /usr/bin/env ruby
# frozen_string_literal: true

# Save as `demo`, then `chmod 755 demo`, and run as `./demo`.

require "bundler/inline"

gemfile true do
  source "https://rubygems.org"

  gem "amazing_print"
  gem "debug"
  gem "lode"
  gem "milestoner"
end

client = Lode.new "demo.store" do |config|
  config.mode = :max
  config.table = Lode::Tables::Value
  config.register :users, model: Milestoner::Models::User, primary_key: :name
end

creator = Milestoner::CLI::Actions::Cache::Create.new(client:)
creator.call "1,zoe,Zoë Washburne"

The above will produce this error:

Fetching gem metadata from https://rubygems.org/...........
Resolving dependencies...
<internal:ractor>:832:in 'Ractor.make_shareable': Proc's self is not shareable: #<Proc:0x0000000160ea17d8 /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/pstore-0.2.0/lib/pstore.rb:673> (Ractor::IsolationError)
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/pstore-0.2.0/lib/pstore.rb:676:in 'PStore#on_windows?'
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/pstore-0.2.0/lib/pstore.rb:685:in 'PStore#save_data'
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/pstore-0.2.0/lib/pstore.rb:575:in 'PStore#transaction'
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/lode-2.2.0/lib/lode/client.rb:34:in 'Lode::Client#transact'
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/lode-2.2.0/lib/lode/client.rb:27:in 'Lode::Client#write'
	from /Users/bkuhlmann/.cache/frum/versions/3.4.2/lib/ruby/gems/3.4.0/gems/milestoner-19.3.0/lib/milestoner/cli/actions/cache/create.rb:23:in 'Milestoner::CLI::Actions::Cache::Create#call'
	from /Users/bkuhlmann/Engineering/Misc/demo:23:in '<main>'

The Lode gem is monadic wrapper around PStore so if you remove config.mode = :max. The issue goes away. The max mode simply wraps PStore's native functionality of ultra_safe = true. In other words, this is equivalent to:

PStore.new("demo.store", true).tap { it.ultra_safe = true }

So you can't use PStore with thread and file safety at the same time anymore?

Notes

If this line is removed, the issue goes away.