From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2022-10-21T05:18:48+00:00
Subject: [ruby-core:110456] [Ruby master Feature#19056] Introduce `Fiber.annotation` for attaching messages to fibers.

Issue #19056 has been updated by mame (Yusuke Endoh).


I think annotation per Fiber will cause conflict in usage between libraries. For example, consider the following library code.

```ruby
def fetch_info_from_url(uri)
  Fiber.new do
    Fiber.annotate "fetching info from #{ uri }"
    URI.open(uri) do |f|
      f.each_line do |line|
        Fiber.yield line
      end
    end
  end
end

f = fetch_info_from_uri("example.com")
p f.resume   #=> first line of example.com
f.annotation #=> "fetching info from example.com"
```

It should work perfect. And then, suppose uri gem has been updated to use `Fiber.annotate` in `URI.open(uri)`.

```ruby
def URI.open(...)
  ...
  Fiber.annotate "calling the user block"
  yield io
  ...
end
```

Now `f.annotation` will return `"calling the user block"` instead of `"fetching info from example.com"`.

What is the bad thing here? Must uri gem not use `Fiber.annotate`? If so, what is allowed to use it?

Also, the message `"calling the user block"` is correct in the context of uri gem, but not very informative for the application authors. However, it is difficult for uri gem to write a more appropriate message because it does not know the context of the entire application.

After all, only the application authors can use `Fiber.annotate`, not library authors. If so, there seems little need to introduce it in the core.

----------------------------------------
Feature #19056: Introduce `Fiber.annotation` for attaching messages to fibers.
https://bugs.ruby-lang.org/issues/19056#change-99773

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
----------------------------------------
It's useful to know what a fiber is doing especially when they have a temporal execution (i.e. sockets connecting vs connected, binding vs accepting, queue popping, etc)

Let's introduce `Fiber.annotate` and `Fiber#annotation` for logging a short message attached to Fibers.

```ruby
Fiber.annotate "Counting to 10"
10.times{|I| puts I}

# Fiber.current.annotation => "Counting to 10"
```

Pull Request: https://github.com/ruby/ruby/pull/6554

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