Ruby

Bug #21119

Updated by genya0407 (Yusuke Sangenya) 10 months ago

Executing the following code in Ruby 3.4.1 takes a very long time, especially when there are many files \(100~\) in the current directory. 
 This delay does not occur in Ruby 3.3.6. 

 ## Reproducible script 

 ```ruby 
 # hoge.rb 

 # Launch a thread to execute CPU-heavy task 
 Thread.new do 
   loop do 
     arr = [] 
     100.times do 
      arr << rand(1...100) 
     end 
   end 
 end 

 # Execute a program containing `Dir.glob` in the main thread. 
 10.times do 
   Dir.glob('*') 
   puts "aaaa" 
 end 
 ``` 

 ## Execution Results 

 Executing Executiong the above code in Ruby 3.4.1 takes **119.43s**. 

 ```shell 
 $ ruby -v 
 ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24] 

 $ time ruby hoge.rb 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 ruby hoge.rb    119.43s user 0.30s system 99% cpu 1:59.89 total 
 ``` 

 Executing it in Ruby master also takes **118.87s**. 

 ```shell 
 $ ~/opt-ruby/bin/ruby -v 
 ruby 3.5.0dev (2025-02-06T14:10:34Z master adbf9c5b36) +PRISM [arm64-darwin24] 

 $ time ~/opt-ruby/bin/ruby hoge.rb 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 ~/opt-ruby/bin/ruby hoge.rb    118.87s user 0.46s system 99% cpu 2:00.45 total 
 ``` 

 Executing it in Ruby 3.3.6 takes only **2.22s**. 

 ```shell 
 $ ruby -v 
 ruby 3.3.6 (2024-11-05 revision 75015d4c1f) [arm64-darwin24] 

 $ time ruby hoge.rb 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 aaaa 
 ruby hoge.rb    2.22s user 0.03s system 98% cpu 2.286 total 
 ``` 

 So, there are roughly **50x** delays. 

 ## Possible Cause 

 From Ruby 3.4.0, `Dir.glob` releases the GVL frequently. 

 * https://bugs.ruby-lang.org/issues/20587 
 * https://github.com/ruby/ruby/pull/11147 

 Due to this change, when a CPU-heavy thread releases the GVL, `Dir.glob` also releases the GVL immediately. 
 As a result, `Dir.glob` gets significantly delayed because it has to continuously regain the GVL causing a major slowdown in execution. 

 ## Note about Execution Results 

 I measured the execution results under a stress condition, with 100 files in the current directory.   
 If there are fewer files, the slowdown may be less pronounced. 

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