01_description.txt

JRuby in 1.9 mode does way too much work every time I require a
file that's previously been required. Here's the output of a
simple script to test this - the first argument is the number of
times to require the same file and the second argument is the
number of entries we put on the load path before requiring that
file.

Current JRuby master:

bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 1
  1.740000   0.080000   1.820000 (  0.614000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 10
  3.220000   0.230000   3.450000 (  1.159000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 100
  4.090000   0.680000   4.770000 (  2.171000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 1000
 11.390000   5.860000  17.250000 ( 13.474000)


JRuby master with a one-line patch included below:

bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 1
  0.550000   0.020000   0.570000 (  0.194000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 10
  0.500000   0.020000   0.520000 (  0.160000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 100
  0.510000   0.020000   0.530000 (  0.172000)
bbrowning@bbrowning-mbp:~/src/jruby(master)$ bin/jruby ~/tmp/duplicate_requires.rb 1000 1000
  1.150000   0.040000   1.190000 (  0.392000)



So, with a load path size of 100 entries (not uncommon for Rails
apps using Bundler), it takes 3.58 seconds longer to require the
same thing 1000 times. That's 3.58 milliseconds of extra time per
require statement.

02_duplicate_requires.rb

require 'benchmark'

iterations = ARGV[0].to_i
load_path_size = ARGV[1].to_i

load_path_size.times do |i|
  $:.unshift "/tmp/foo#{i}"
end

puts Benchmark.measure {
  iterations.times do
    require 'erb'
  end
}

03_loadservice.diff

diff --git a/src/org/jruby/runtime/load/LoadService.java b/src/org/jruby/runtime/load/LoadService.java
index 5f9645b..0d11a54 100644
--- a/src/org/jruby/runtime/load/LoadService.java
+++ b/src/org/jruby/runtime/load/LoadService.java
@@ -537,6 +537,7 @@ public class LoadService {
         boolean loaded = tryLoadingLibraryOrScript(runtime, state);
         if (loaded) {
             addLoadedFeature(state.loadName);
+            addLoadedFeature(file);
         }
         return loaded;
     }