[ruby-core:103911] [Ruby master Feature#17849] Fix Timeout.timeout so that it can be used in threaded Web servers

Issue #17849 has been updated by Eregon (Benoit Daloze).


I think (2) is rare, and IMHO such programs should be fixed.
What would happen is then those programs can't be interrupted (only by killing the process), but then that also becomes a clear motivation to fix those programs so they can be interrutped safely.

Not sure about (1), I think it's loading the current thread + saving current value of the mask, writing the interrupt mask for every `ensure`, and restoring it once the `ensure` finishes.
It needs to be done on the non-exceptional path too, so indeed it could be some overhead.
I think we need to measure it in practice here to evaluate better the overhead.

The whole strategy here relies on code in `ensure` having code that only takes a small amount of time.
If that doesn't hold, it will either hang (motivating those programs to be fixed),
or we could resort to the old semantics after some extra time (e.g., 10s), similar to what https://bugs.ruby-lang.org/issues/17849#note-3 proposes, and then print a big warning that the program misbehaved (and that state might be corrupted due to that as `ensure` likely has been interrupted).
That could be useful notably for Ctrl+C to still work as it does currently in such situations.

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Feature #17849: Fix Timeout.timeout so that it can be used in threaded Web servers
https://bugs.ruby-lang.org/issues/17849#change-92040

* Author: duerst (Martin Dst)
* Status: Open
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
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Making this a separate issue from #17837

Eregon (Benoit Daloze) wrote in https://bugs.ruby-lang.org/issues/17837#note-10 (which is  about timeouts for regular expressions):

> I think fixing Timeout.timeout might be possible.
> The main/major issue is it can trigger within `ensure`, right? Is there anything else?
> We could automatically mask `Thread#raise` within `ensure` so it only happens after the `ensure` body completes.
> And we could still have a larger "hard timeout" if an `ensure` takes way too long (shouldn't happen, but one cannot be sure).
> I recall discussing this with @schneems some time ago on Twitter.





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