Feature #21942: Allow reading class variables from non-main Ractors

• Status: Closed
• Assignee: ractor
• Target version: -

[tenderlovemaking (Aaron Patterson)]

It's very common in Rails applications to use class variables, and today class variables aren't even allowed to be read inside a Ractor:

class Foo
  # This is NOT allowed to be read in non-main Ractors
  @@bar = 123
  def self.bar; @@bar; end

  # This is allowed to be read in non-main Ractors
  @baz = 123
  def self.baz; @baz; end
end

# This is OK
Ractor.new {
  p Foo.baz
}.value

# Exception here
Ractor.new {
  p Foo.bar
}.value

Output is like this:

test.rb:4:in 'Foo.bar': can not access class variables from non-main Ractors (@@bar from Foo) (Ractor::IsolationError)
	from test.rb:10:in 'block in <main>'

Can we allow shareable values to cross the Ractor boundary, similar to class instance variables?

Just for reference, the Rails code in question is here.

[tenderlovemaking (Aaron Patterson)]

I sent a patch here

[tenderlovemaking (Aaron Patterson)]

• Assignee set to ractor

[tenderlovemaking (Aaron Patterson)]

• Status changed from Open to Closed

Applied in changeset git|ab32c0e690b805cdaaf264ad4c3421696c588204.

---

Allow reading cvars from non-main Ractors (#16308)

Today you can read instance variables from non-main Ractors, but many
Rails applications use cvars, and we cannot read them.

For example:

class Foo
  # This is NOT allowed to be read in non-main Ractors
  @@bar = 123
  def self.bar; @@bar; end

  # This is allowed to be read in non-main Ractors
  @baz = 123
  def self.baz; @baz; end
end

  # This is OK
Ractor.new {
  p Foo.baz
}.value

  # Exception here
Ractor.new {
  p Foo.bar
}.value

This commit changes the semantics of cvars to be the same as instance
variables:

• It's ok to read Ractor shareable objects from the non-main Ractor
• It's NOT ok to write from the non-main Ractor

[Feature #21942]