From: "k0kubun (Takashi Kokubun) via ruby-core" <ruby-core@...>
Date: 2026-03-16T18:57:49+00:00
Subject: [ruby-core:125018] [Ruby Bug#21947] `Timeout.timeout` doesn't use `Timeout::ExitException` when Fiber scheduler is in use.

Issue #21947 has been updated by k0kubun (Takashi Kokubun).

Backport changed from 3.3: REQUIRED, 3.4: REQUIRED, 4.0: REQUIRED to 3.3: REQUIRED, 3.4: REQUIRED, 4.0: DONE

ruby_4_0 commit:f808ff5fc15690338dcb6530e4d3df760d8721f3 merged revision(s) commit:f315d250b44e75a1a69f4a05b293dcc701377689.

----------------------------------------
Bug #21947: `Timeout.timeout` doesn't use `Timeout::ExitException` when Fiber scheduler is in use.
https://bugs.ruby-lang.org/issues/21947#change-116715

* Author: ioquatix (Samuel Williams)
* Status: Closed
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.3: REQUIRED, 3.4: REQUIRED, 4.0: DONE
----------------------------------------
The following example executes successfully after 7 seconds instead of timing out after 2.

```ruby
require 'async'
require 'net/http'

start = Time.now

Sync do
  Timeout.timeout 2 do
    Net::HTTP.get(URI 'https://httpbin.org/delay/5')

    puts "...request finished, no timeout though; in #{Time.now - start}s"
  end
end

puts "Duration: #{Time.now - start}s"

# => ...request finished, no timeout though; in 7.7007s
# Duration: 7.700962s
```

There are two issues:

- `Net::HTTP` rescues `Timeout::Error` and retries. This causes 2s (timeout -> retry) + 5s execution time.
- `Timeout.timeout` uses `Timeout::ExitException` when no exception is specified, but the Fiber scheduler code path was not updated.

See <https://github.com/socketry/async/issues/448> for more discussion.



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