Feature #21532
open
Define most of Pathname in Ruby code
Description
There was discussion in #17473 and before to define most of Pathname in Ruby code and not in the C extension.
I have made a PR to achieve that: https://github.com/ruby/pathname/pull/57
I would like to merge it soon to avoid conflicts.
Once upon a time, Pathname was pure-Ruby: https://github.com/ruby/ruby/blob/95bc02237635d3fe42532bfe53038257575cee75/lib/pathname.rb
This PR goes back to that, and reuses that original Ruby code, but keeps the C extension implementation of <=> and sub as those two are significantly faster.
The other Pathname methods are actually faster in Ruby than in C, because all these methods just do rb_funcall() and rb_ivar_get() and those in C code have no inline cache, but the corresponding method calls and @path have inline caches in Ruby code.
https://railsatscale.com/2023-08-29-ruby-outperforms-c/ is an explanation of that.
Therefore having Pathname defined in Ruby seems a clear win for many reasons:
- Much clearer implementation, so easier to read what the code does
- Easier to maintain
- Safer (no risk of accessing out of bounds memory or e.g. passing the wrong number of arguments to
rb_funcall) - Significantly faster, because of these inline caches (more details in https://github.com/ruby/pathname/pull/57#issue-3234862768):
| Speedup (this branch / master) | ruby 3.4.2 | ruby 3.4.2 + YJIT |
|---|---|---|
Pathname.new(".") |
1.02x | 1.19x |
Pathname#directory? |
1.03x | 1.06x |
Pathname#to_s |
1.85x | 2.38x |
- Better for JITs as they can optimize this, notably
...vs the C extension being a blackbox - Works on JRuby (which does not support C extensions)
- Works on TruffleRuby (some Ruby C API functions that the extension uses are not supported on TruffleRuby)
Updated by Eregon (Benoit Daloze) about 19 hours ago
- Related to Feature #17473: Make Pathname to embedded class of Ruby added