[ruby-core:104716] [Ruby master Bug#10902] require("enumerator") scans LOAD_PATH 2x on every invocation

Issue #10902 has been updated by Eregon (Benoit Daloze).


IMHO it would be fine to simply not allow loading any `foo.rb` if `foo.so` is already loaded, a change of semantics which would gain a lot of simplicity.
Do we have actual use cases for `require "foo"` to first load `foo.so` and then later on another `require "foo"` to load `foo.rb`?
It seems unlikely to be intentional behavior.
I argue users should at least specify the extension in both cases if they expect that.

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Bug #10902: require("enumerator") scans LOAD_PATH 2x on every invocation
https://bugs.ruby-lang.org/issues/10902#change-93043

* Author: tmm1 (Aman Gupta)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 2.1.5
* Backport: 2.7: REQUIRED, 3.0: REQUIRED
----------------------------------------
On every invocation of `require "enumerator"` (for example during boot when many gems require it), the VM will scan the load path twice: once for enumerator.rb and again for enumerator.so. Of course, no file is found because enumerator is now shipped within the VM by default.

~~~
$ ruby -e' p $LOADED_FEATURES[0] '
"enumerator.so"

$ ruby -e' p $LOAD_PATH.size '
8

$ strace -e trace=open ruby -e' 1.times{ require "enumerator" } ' 2>&1 | grep enumerator.rb | wc -l
8

$ strace -e trace=open ruby -e' 1.times{ require "enumerator" } ' 2>&1 | grep enumerator.so | wc -l
8

$ strace -e trace=open ruby -e' 10.times{ require "enumerator" } ' 2>&1 | grep enumerator.so | wc -l
80

$ strace -e trace=open ruby -e' 100.times{ require "enumerator" } ' 2>&1 | grep enumerator.so | wc -l
800
~~~

In enumerator.c, we call `rb_provide("enumerator.so")` which adds it to $LOADED_FEATURES. This means `require "enumerator.so"` can be optimized, but most libraries do not include the .so extension when requiring enumerator.



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