From: "ioquatix (Samuel Williams)" <noreply@...>
Date: 2022-10-16T10:31:05+00:00
Subject: [ruby-core:110320] [Ruby master Bug#19062] Introduce `Fiber#locals` for shared inheritable state.

Issue #19062 has been reported by ioquatix (Samuel Williams).

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Bug #19062: Introduce `Fiber#locals` for shared inheritable state.
https://bugs.ruby-lang.org/issues/19062

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
After exploring <https://bugs.ruby-lang.org/issues/19058>, I felt uncomfortable about the performance issue of lots of inheritable attributes. Please review that issue for the background and summary of the problem.

## Proposal

Introduce `Fiber#locals` which is a hash table of local attributes which are inherited by child fibers.

```ruby
Fiber.current.locals[:x] = 10

Fiber.new do
  pp Fiber.current.locals[:x] # => 10
end
```

It's possible to reset `Fiber.current.locals`, e.g.

```ruby
def accept_connection(peer)
  Fiber.new(locals: nil) do # This causes a new hash table to be allocated.
    # Generate a new request id for all fibers nested in this one:
    Fiber[:request_id] = SecureRandom.hex(32)
    @app.call(env)
  end.resume
end
```

Pull Request: https://github.com/ruby/ruby/pull/6566



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