From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2024-02-20T10:55:28+00:00
Subject: [ruby-core:116873] [Ruby master Bug#20284] Regexp::TimeoutError is not triggered by a specific Regexp

Issue #20284 has been updated by mame (Yusuke Endoh).

Status changed from Open to Feedback

Thanks for the report.

This takes a long time in the preprocessing part before regexp matching. I think this process is O(n) for the length n of the input string. Since `Regexp.timeout=` is a countermeasure against super-linear behavior, I feel this is not a big deal. And frankly, I can't think of a good idea to fix it.

It is also known that the timeout do not work for very large regexps that contain no instruction that checks timeouts. Maybe I should update the documentation?

Let me know if anyone has a nice idea to fix it.

----------------------------------------
Bug #20284: Regexp::TimeoutError is not triggered by a specific Regexp
https://bugs.ruby-lang.org/issues/20284#change-106908

* Author: jbeschi (jacopo beschi)
* Status: Feedback
* Priority: Normal
* ruby -v: 3.3.0
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
I've noticed that the Regexp::TimeoutError is not triggered for this Regexp:


```ruby
jacopo-37s-mb 3.3.0 ~ cat fail.rb
require 'benchmark'

p RUBY_DESCRIPTION
Regexp.timeout = 0.1
puts "Regexp.timeout: #{Regexp.timeout}"
re = /((a|aa)+)+b/
10.times do
  p Benchmark.realtime { re.match?("a" * 900000000) }
end
```

```
jacopo-37s-mb 3.3.0 ~ ruby fail.rb
"ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin22]"
Regexp.timeout: 0.1
1.1425850000232458
1.0082139987498522
1.064377998933196
1.0745620001107454
1.0647990014404058
1.6172770000994205
1.396629998460412
1.2450549993664026
1.3292079996317625
1.5961690004915
```



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