[ruby-core:118709] [Ruby master Misc#20652] Memory allocation for gsub has increased from Ruby 2.7 to 3.3
From:
"Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date:
2024-07-27 10:58:24 UTC
List:
ruby-core #118709
Issue #20652 has been updated by Eregon (Benoit Daloze).
ko1 (Koichi Sasada) wrote in #note-8:
> what does it happen when creating a thread just after storing `$~`?
It's simply not set in the new thread, and that seems already the same behavior on CRuby:
```
$ ruby -ve '"a" =~ /a/; p $~; Thread.new { p $~ }.join'
ruby 3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux]
#<MatchData "a">
nil
$ ruby -ve '"a" =~ /a/; p $~; Thread.new { p $~ }.join'
truffleruby 24.1.0-dev-c2e5209c, like ruby 3.2.2, GraalVM CE Native [x86_64-linux]
#<MatchData "a">
nil
```
ko1 (Koichi Sasada) wrote in #note-11:
> I found an idea that each thread points to unescaped MatchData rather than `$~` and reuse it.
I think that's too incompatible because `$~` is frame-local and thread-local, so we need multiple `$~` per thread, as @byroot showed.
----------------------------------------
Misc #20652: Memory allocation for gsub has increased from Ruby 2.7 to 3.3
https://bugs.ruby-lang.org/issues/20652#change-109244
* Author: orisano (Nao Yonashiro)
* Status: Open
* Assignee: jeremyevans0 (Jeremy Evans)
----------------------------------------
I recently upgraded from ruby 2.7.7 to 3.3.1 and noticed that the GC load increased.
When I used the allocation profiler to investigate, I found that memory allocation from gsub had increased.
The problem was code like this:
```ruby
s = "foo "
s.gsub(/ (\s+)/) { " #{' ' * Regexp.last_match(1).length}" }
```
When I compared the results of heap-profiler between 2.7.7 and 3.3.1, I found that MatchData was increasing.
https://gist.github.com/orisano/98792dee260106e9b6fcb45bbabeb1e6
https://github.com/ruby/ruby/commit/abc0304cb28cb9dcc3476993bc487884c139fd11
I discovered that the cause is this commit, which stopped reusing backref to avoid race conditions.
Is there a way to reuse backref while still avoiding race conditions?
--
https://bugs.ruby-lang.org/
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