An attempt to provide a minimal reproduction of a threading-related JRuby problem

README.md

While working on https://github.com/fidothe/saxon-rb I hit errors in production using a semi-experimental branch (https://github.com/fidothe/saxon-rb/tree/error-reporting) in a threaded XML-processing program.

The errors were the same NoMethodError: undefined method __jcreate_meta!' as in jruby/jruby#6160, and the program structure is almost identical save for some loading indirection thanks to the use of autoload.

I am running it in a CI-type environment where 20+ EC2 instances are spun up to process a large amount of data. Most, but not all, runs I'd have one instance's process crash with the error.

Creating an instance of the problem class (https://github.com/fidothe/saxon-rb/blob/error-reporting/lib/saxon/error_reporter.rb, EgClass in this reproduction case) on the main thread, rather than in the worker threads, has made the problem vanish entirely.

tortuous-example-autoload.rb

require 'java'

module TortuousExample
  class EgClass
    def self.setup
      include java.lang.Comparable
    end

    attr_reader :val

    def initialize(val)
      self.class.setup
      @val = val
    end

    def compareTo(other)
      val <=> other.val
    end
  end
end

tortuous-example.rb

require 'thread'
require 'pathname'

module TortuousExample
  autoload :EgClass, (Pathname.new(__FILE__)/'../tortuous-example-autoload.rb').realpath
end

(1..8).map {
  Thread.new {
    sleep 0.5
    print "."
    TortuousExample::EgClass.new(rand(100))
  }
}.each(&:join)
puts ""