[ruby-core:108008] [Ruby master Feature#18630] Introduce general `IO#timeout` and `IO#timeout=`for all (non-)blocking operations.

Issue #18630 has been updated by Eregon (Benoit Daloze).


I guess one way to express it is this new IO#timeout would apply to: blocking IO methods on non-blocking IO instances.

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Feature #18630: Introduce general `IO#timeout` and `IO#timeout=`for all (non-)blocking operations.
https://bugs.ruby-lang.org/issues/18630#change-96964

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
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I would like us to consider introducing a general timeout for all blocking operations. This timeout can be specified per IO instance. It's useful for ensuring programs don't stop responding or spend an unreasonable amount of time waiting for IO operations.

There are effectively two kinds of interfaces that we need to address:

- Those that already have a timeout argument (e.g. `wait_readable`) and we follow the existing semantics.
- Those that don't have a timeout argument or timeout semantics (e.g. `puts`, `gets`), and thus probably need to raise an exception on timeout.

We have three possible kinds of exceptions we could raise:

- `Errno::ETIMEDOUT`
- `Timeout::Error` (from `timeout.rb`)
- Introduce `IO::Timeout` or something similar.

Timeout isn't necessarily an error condition. There are different arguments for whether we should define:

```ruby
class IO::Timeout < Exception
end

# or

class IO::Timeout < StandardError
end
```

I believe the latter (`StandardError`) is more practical but I'm open to either option. I might have more specific arguments later why one is better than the other after testing in a practical system.

There is already a PR to try it out: https://github.com/ruby/ruby/pull/5653



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