[GR-18163] Avoid loading RubyGems needlessly for require 'psych'

PullRequest: truffleruby/2077

Author: eregon

doc/contributor/profiling.md

@@ -82,7 +82,7 @@ The `--metrics-profile-require` option can be used to profile the time used for
 
 For example, the `summary` view provides an overview of where time is spent:
 ```
-$ jt ruby --experimental-options --cpusampler --cpusampler.Mode=roots --metrics-profile-require=summary -e 'require "rubygems"' |& grep "metrics "
+$ jt ruby --experimental-options --cpusampler --metrics-profile-require=summary -e 'require "rubygems"' |& grep "metrics "
  metrics execute                                                      |       1122ms  99.6% |   0.0% ||        212ms  18.8% |   0.0% | (metrics)~1:0 
  metrics parsing                                                      |         71ms   6.3% |   0.0% ||         71ms   6.3% |   0.0% | (metrics)~1:0 
  metrics translating                                                  |         60ms   5.3% |   0.0% ||         60ms   5.3% |   0.0% | (metrics)~1:0 
@@ -92,4 +92,4 @@ $ jt ruby --experimental-options --cpusampler --cpusampler.Mode=roots --metrics-
 
 This feature can also be used to generate a flame graph with detailed require timings:
 
-`$ jt profile --experimental-options --cpusampler --cpusampler.Mode=roots --metrics-profile-require=detail -e 'require "rubygems"'`
+`$ jt profile --metrics-profile-require=detail -e 'require "rubygems"'`

lib/mri/psych.rb

@@ -10,11 +10,12 @@
     org.jruby.ext.psych.PsychLibrary.new.load(JRuby.runtime, false)
   end
 else
-  begin
-    require "#{RUBY_VERSION[/\d+\.\d+/]}/psych.so"
-  rescue LoadError
+  # TruffleRuby: avoid requiring a non-existing file, which would trigger loading RubyGems
+  # begin
+  #   require "#{RUBY_VERSION[/\d+\.\d+/]}/psych.so"
+  # rescue LoadError
     require 'psych.so'
-  end
+  # end
 end
 require 'psych/nodes'
 require 'psych/streaming'

spec/tags/truffle/lazy_rubygems_tags.txt

@@ -4,3 +4,4 @@ slow:RubyGems is loaded by a failing require
 slow:Lazy RubyGems defines StringIO like RubyGems which requires it eagerly
 slow:Lazy RubyGems works for require 'rubygems/package'
 slow:Lazy RubyGems works for require 'rubygems/specification'
+slow:RubyGems is not loaded for default gems if there is no upgraded default gem

spec/truffle/lazy_rubygems_spec.rb

@@ -15,6 +15,33 @@
     ruby_exe('p autoload? :Gem').should == "\"rubygems\"\n"
   end
 
+  # This spec needs no upgraded gems installed
+  it "is not loaded for default gems if there is no upgraded default gem" do
+    default_gems = Truffle::GemUtil::DEFAULT_GEMS.keys
+    default_gems -= [
+      'bundler', # explicitly requires RubyGems
+      'dbm', 'gdbm', 'sdbm', # not available
+      'rss', # rss/xmlparser.rb requires non-existing "xml/parser"
+    ]
+    default_gems.delete('io')
+    default_gems << 'io/console'
+    default_gems.delete('rexml')
+    default_gems << 'rexml/document'
+
+    code = <<-RUBY
+    #{default_gems.inspect}.each do |name|
+      require name
+      unless autoload?(:Gem) == "rubygems"
+        puts $LOADED_FEATURES
+        abort "\#{name} loaded RubyGems"
+      end
+    end
+    puts 'OK'
+    RUBY
+    ruby_exe(code, args: "2>&1").should == "OK\n"
+    $?.success?.should == true
+  end
+
   it "is loaded when accessing Gem" do
     ruby_exe('Gem; puts $"').should include('/rubygems.rb')
     ruby_exe('Gem; p autoload? :Gem').should == "nil\n"

tool/jt.rb

@@ -1886,7 +1886,8 @@ def profile(*args)
       }
     end
     raw_sh "#{repo}/stackcollapse-graalvm.rb", profile_data_file, out: flamegraph_data_file
-    raw_sh "#{repo}/flamegraph.pl", flamegraph_data_file, out: svg_filename
+    unit = args.any?(/^--cpusampler\.Period=/) ? [] : ['--countname', 'ms']
+    raw_sh "#{repo}/flamegraph.pl", *unit, flamegraph_data_file, out: svg_filename
 
     app_open svg_filename
   end