From: "fxn (Xavier Noria) via ruby-core" <ruby-core@...>
Date: 2025-06-08T06:52:03+00:00
Subject: [ruby-core:122492] [Ruby Bug#19154] Specify require and autoload guarantees in ractors

Issue #19154 has been updated by fxn (Xavier Noria).


Is constant access synchronized as it is for threads?

If a constant has an autoload set and 7 threads hit it, only one of them autoloads, and the rest block until that autoload has finished. This includes the case in which the winner thread has defined the constant and there is a context switch, the rest pass and wait until the ongoing autoload is complete.

----------------------------------------
Bug #19154: Specify require and autoload guarantees in ractors
https://bugs.ruby-lang.org/issues/19154#change-113681

* Author: fxn (Xavier Noria)
* Status: Assigned
* Assignee: ractor
* 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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