arel-visitor-thread-safe-test.rb

# frozen_string_literal: true
module Arel
  module Visitors
    class Visitor
      def initialize
        @dispatch = get_dispatch_cache
        @random = [0.1, 0.5, 1, 2, 4]
      end

      def accept object
        visit object
      end

      private

      def self.dispatch_cache
        Hash.new do |hash, klass|
          hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
        end
      end

      def get_dispatch_cache
        self.class.dispatch_cache
      end

      def dispatch
        @dispatch
      end

      def visit object
        sleep @random.sample
        dispatch_method = dispatch[object.class]
        send dispatch_method, object
      rescue NoMethodError => e
        puts "HERE"
        sleep @random.sample
        raise e if respond_to?(dispatch_method, true)
        superklass = object.class.ancestors.find { |klass|
          respond_to?(dispatch[klass], true)
        }
        raise(TypeError, "Cannot visit #{object.class}") unless superklass
        dispatch[object.class] = dispatch[superklass]
        retry
      end
    end
  end
end




# frozen_string_literal: true
require 'helper'

module Arel
  module Visitors
    describe 'avoiding contamination between visitor dispatch tables' do
      before do
        @connection = Table.engine.connection
        @table = Table.new(:users)
      end

      it 'dispatches properly after failing upwards' do
        node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
        assert_equal "( TRUE UNION FALSE )", node.to_sql

        node.first # from Nodes::Node's Enumerable mixin

        assert_equal "( TRUE UNION FALSE )", node.to_sql
      end


      it 'does not throw NoMethodError when multi-threaded defining "visit"' do
        ::Thread.abort_on_exception = true
        threads = []

        20.times do
          threads << ::Thread.new do
            puts "thread opened"
            10.times do
              node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
              assert_equal "( TRUE UNION FALSE )", node.to_sql

              node.first # from Nodes::Node's Enumerable mixin

              assert_equal "( TRUE UNION FALSE )", node.to_sql
            end
            puts "thread done"
          end
        end

        threads.map(&:join)
      end
    end
  end
end