From: shevegen@... Date: 2020-06-06T11:39:05+00:00 Subject: [ruby-core:98664] [Ruby master Feature#16848] Allow callables in $LOAD_PATH Issue #16848 has been updated by shevegen (Robert A. Heiler). This was recently discussed: https://github.com/ruby/dev-meeting-log/blob/master/DevelopersMeeting20200514Japan.md ko1 will reply. I have no particular opinion per se on this suggestion. But one thing made me curious: require "foo" # load my_app/foo.rb require "bar" # load /gems/bar/bar.rb require "baz" # load /gems/baz/baz.rb require "qux" # load /stdlib/qux.rb This would be quite nice in that we do not have to provide a specific path to a .rb file. This could also help if you relocate files, from one path to another - if you specify the hardcoded path, if that is changed, you have to modify all links that point to that .rb file. My totally unfinished idea is to propose being able to omit all require statements. :) Perhaps only make it limited to gem releases where the ruby user no longer has to supply a full path, and then update it if it changes. Something like an API for requires that allows us to be unspecific. I understand that this is not what byroot suggested, so I should make a separate issue suggestion. But I wanted to mention it because it sort of taps into a related idea - make it easier to handle require of files. This is something I have to do almost daily when I write ruby code - I have to find where code is, then load that code and make sure all require lines are correct. This is a bit cumbersome. ---------------------------------------- Feature #16848: Allow callables in $LOAD_PATH https://bugs.ruby-lang.org/issues/16848#change-86009 * Author: byroot (Jean Boussier) * Status: Feedback * Priority: Normal ---------------------------------------- Make it easier to implement `$LOAD_PATH` caching, and speed up application boot time. I benchmarked it on Redmine's master using bootsnap with only the optimization enabled: ```ruby if ENV['CACHE_LOAD_PATH'] require 'bootsnap' Bootsnap.setup( cache_dir: 'tmp/cache', development_mode: false, load_path_cache: true, autoload_paths_cache: true, disable_trace: false, compile_cache_iseq: true, compile_cache_yaml: false, ) end ``` ``` $ RAILS_ENV=production time bin/rails runner 'p 1' 2.66 real 1.99 user 0.66 sys $ RAILS_ENV=production time bin/rails runner 'p 1' 2.71 real 1.97 user 0.66 sys $ CACHE_LOAD_PATH=1 RAILS_ENV=production time bin/rails runner 'p 1' 1.41 real 1.12 user 0.28 sys $ CACHE_LOAD_PATH=1 RAILS_ENV=production time bin/rails runner 'p 1' 1.41 real 1.12 user 0.28 sys ``` That's twice for a relatively small application. And the performance improvement is not linear; the larger the application, the larger the improvement. ### How it works `require` has `O($LOAD_PATH.size)` performance. The more gems you add to your `Gemfile`, the larger `$LOAD_PATH` becomes. `require "foo.rb"` will try to open the file in each of the `$LOAD_PATH` entries. And since more gems usually also means more `require` calls, loading Ruby code may take up to quadratic performance loss. To improve this, Bootsnap pre-computes a map of all the files in your `$LOAD_PATH`, and uses it to convert relative paths into absolute paths so that Ruby skips the `$LOAD_PATH` traversal. ```ruby $LOAD_PATH = $w(/gems/foo/lib /gems/bar/lib) BOOTSNAP_CACHE = { "bar.rb" => "/gems/bar/lib/bar.rb", } ``` This resolves file lookup by a single hash lookup, and reduces boot performance from roughly `O($LOAD_PATH.size * number_of_files_to_require)` to `O(number_of_files_to_require)`. This optimization is also used in [Gel](https://github.com/gel-rb/gel), a Rubygems/Bundler replacement. ### Trade offs Every time `$LOAD_PATH` is modified, the cache must become invalidated. While this is complex to do for Bootsnap, it would be fairly easy if it is implemented inside Ruby. More importantly, you have to invalidate the cache whenever you add or delete a file to/from one of the `$LOAD_PATH` members; otherwise, if you shadow or unshadow another file farther in the `$LOAD_PATH`, Bootsnap will load a wrong file. For instance, if `require "foo.rb"` initially resolves to `/some/gem/foo.rb`, and you create `lib/foo.rb`, you'll need to flush Bootsnap cache. That latter is trickier, and Bootsnap has decided that it is rare enough to cause actual problems, and so far that holds. But that is not a trade off Ruby can make. However that's probably a tradeoff Rubygems/Bundler can make. While it's common to edit your gems to debug something, it's really uncommon to add or remove files inside them. So in theory Rubygems/Bundler could compute a map of all files in a gem that can be required after it installs it. Then when you activate it, you merge it together with the other activated gems. ### Proposal This could be reasonably easy to implement if `$LOAD_PATH` accepted callables in addition to paths. Something like this: ```ruby $LOAD_PATH = [ 'my_app/lib', BundlerOrRubygems.method(:lookup), ] ``` The contract would be that `BundlerOrRubygems.lookup("some_relative/path.rb")` would return either an absolute path or `nil`. With such API, it would be easy to cache absolute paths only for gems and the stdlib, and preserve the current cache-less behavior for the application specific load paths, which are usually much less numerous. It would also allow frameworks such as Rails to implement the same caching for application paths when running in an environment where the source files are immutable (typically production). -- https://bugs.ruby-lang.org/ Unsubscribe: