[ruby-core:118542] [Ruby master Bug#20627] `require` on Ractor should run on the main Ractor

["ko1 (Koichi Sasada) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20627 has been reported by ko1 (Koichi Sasada).

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Bug #20627: `require` on Ractor should run on the main Ractor
https://bugs.ruby-lang.org/issues/20627

* Author: ko1 (Koichi Sasada)
* Status: Open
* Assignee: ko1 (Koichi Sasada)
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
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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.

![](clipboard-202407111201-kaiem.png)

(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

- `Rcator.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](https://github.com/ruby/ruby/blob/master/lib/rubygems/core_ext/kernel_require.rb#L36).

```ruby
alias orig_require require

def require feature
  return Rator.require(feature) unless Ractor.main?

  # overriding require code
end
```

Or we can prepend a module like:

```
Module.new do
  def require(feature)
    return Rator.require(feature) unless 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)


---Files--------------------------------
clipboard-202407111201-kaiem.png (70.8 KB)


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