[ruby-core:108145] [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).


AFAIK Errno::* is only meant for what the libc/syscalls would return, nothing else, so doesn't fit here.
As said above, many of functions involved above don't ever return ETIMEDOUT, so it would be incorrect/surprising to reuse it for that.

Re naming `Errno::E*`, the "Error" is in the name, twice, it's "Error numero::ERROR abbreviation" ;)
Most of the other exceptions have something that is closely related to error/exception in their name.

It's not because there is "Error" in the name that the exception class should be treated "as an error".
There is simply no such relation, and as you can see there are exception classes with Error in the name both under StandardError and above it too.
They are all exceptions, and whether it is "an error" almost always depends on the context.
The only meaningful distinction AFAIK in Ruby is < StandardError or not. And since it's meant to be rescued in some cases, and for consistency will all other timeout exceptions, it should be < StandardError.

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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-97121

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
I would like us to consider introducing a general IO timeout for all (non-)blocking operations, 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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