Bug #20627: `require` on Ractor should run on the main Ractor

• Status: Open
• Assignee: ko1 (Koichi Sasada)
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[ko1 (Koichi Sasada)]

Now require on main Ractor is not allowed (raising error) but it is hard, especially for autoload.
So let's allow require by running it on the main Ractor.

Background

On many libraries it is needed to run loading on the main Ractors because:

1. Setup constants with unshareable objects (such as C = []) are not allowed on non main Ractors.
2. Setup global variables and class variables are not allowed. $LOADED_FEATURES is also untouchable.
3. (maybe more reasons)

So the require on non main Ractors is not allowed.

However it is hard to program especially on autoload.
Also dynamic require (require in methods) are not allowed too (pp method, for example).

Proposal

Allow require on non main Ractors by running require process on the main Ractor.

(quoted on my talk at RubyKaigi 2024)

rb_ractor_interrupt_exec(target_ractor, func) C-API

Make a thread on target_ractor and run func (C function) on it.

I think it is safe to expose on Ruby API because running func on a newly created thread (do not disturb running target threads). But now it is proposed as only (hidden) C-API.

New Ractor methods

• Ractor.main? returns Ractors
• Ractor.require(feature) do require on the main Ractor

These new methods are useful for users who override require method like RubyGems.

alias orig_require require

def require feature
  return Rator.require(feature) if defined?(Ractor.main?) && !Ractor.main?

  # overriding require code
end

Or we can prepend a module like:

Module.new do
  def require(feature)
    return Rator.require(feature) if defined?(Ractor.main?) && !Ractor.main?
    super(feature)
  end
  Kernel.prepend self
end  

will support ractors for all overgrinding methods. But not sure it is acceptable to add additional one modules in ancestors by prepend.

Also this technique doesn't support require overriding by prepending.

Implementation

https://github.com/ruby/ruby/pull/11142 (not matured yet)

[ko1 (Koichi Sasada)]

• Description updated (diff)

[ko1 (Koichi Sasada)]

• Description updated (diff)

[ko1 (Koichi Sasada)]

• Description updated (diff)

[luke-gru (Luke Gruber)]

Now require on main Ractor is not allowed (raising error)

I think you mean non-main Ractor. I like this change, I think it's necessary to get wider adoption for Ractors due to the autoload issue you mentioned. The change should be documented well in the require docs and the Ractor docs once the implementation is mature since it's a fairly major change imo.