[ruby-core:111814] [Ruby master Bug#19154] Specify require and autoload guarantees in ractors

["luke-gru (Luke Gruber) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #19154 has been updated by luke-gru (Luke Gruber).


I've taken a look at this a bit and got this working:

```ruby
require 'rubygems' # get rubygems version of require
rs = []
100.times do
  rs << Ractor.new do
    require './c.rb'
  end
end
rs.each(&:take)
p C
```
In file c.rb, it's
```ruby
class C
  puts "GOT HERE"
end
```

And it works correctly, only printing "GOT HERE" once and defining C once.
I've had to make several small changes to the interpreter to enable setting ivars and class variables on classes and modules.

I've also added an API of `Ractor.force_shareable!(obj)` that forces the shareable flag on the object and all nested objects that it contains. This is necessary for certain
objects like monitor objects and other deeply nested objects. I only had to add `Ractor.force_shareable!` to 2 or 3 places and requiring gems now works across Ractors. I didn't add any
tests but I might add some if other people are interested in this work.

Also I'll take a look at `autoload`. I know for some, forcing objects to be marked as shareable is a bit unsavory but as long as you know what you're doing it should be okay, like the rust escape hatch of `unsafe`.

----------------------------------------
Bug #19154: Specify require and autoload guarantees in ractors
https://bugs.ruby-lang.org/issues/19154#change-101222

* Author: fxn (Xavier Noria)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0preview3 (2022-11-27) [x86_64-darwin22]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Given a file `c.rb`:

```ruby
class C
end
```

the following script:

```ruby
r1 = Ractor.new do
  require './c.rb'
end

r2 = Ractor.new do
  require './c.rb'
end

r1.take
r2.take
```

raises:

```
% ruby -v foo.rb
ruby 3.2.0preview3 (2022-11-27) [x86_64-darwin22]
foo.rb:1: warning: Ractor is experimental, and the behavior may change in future versions of Ruby! Also there are many implementation issues.
#<Thread:0x000000010fee2928 run> terminated with exception (report_on_exception is true):
#<Thread:0x00000001102acfe0 run> terminated with exception (report_on_exception is true):
<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:164:in `ensure in require': can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)
        from <internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:167:in `require'
        from foo.rb:6:in `block in <main>'
<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:37:in `require'<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:164:in `ensure in require': : can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)
        from <internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:167:in `require'
can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)       from foo.rb:2:in `block in <main>'

<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:37:in `require': can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)
        from foo.rb:2:in `block in <main>'
        from foo.rb:6:in `block in <main>'
<internal:ractor>:698:in `take': thrown by remote Ractor. (Ractor::RemoteError)
        from foo.rb:9:in `<main>'
<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:164:in `ensure in require': can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)
        from <internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:167:in `require'
        from foo.rb:2:in `block in <main>'
<internal:/Users/fxn/.rbenv/versions/3.2.0-preview3/lib/ruby/3.2.0+3/rubygems/core_ext/kernel_require.rb>:37:in `require': can not access non-shareable objects in constant Kernel::RUBYGEMS_ACTIVATION_MONITOR by non-main ractor. (Ractor::IsolationError)
        from foo.rb:2:in `block in <main>'
```

Would it be possible to have documentation about their interaction?

This is important also to understand autoloading within ractors, since constant references may trigger `require` calls.



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