schedule blocks to run in single thread

block-scheduler.rb

require 'thread'

# input_queue = Queue.new

# computer = Thread.new do
#   loop do
#     x, y, block, output_queue = input_queue.pop
#     puts "computing #{x} + #{y}"
#     sleep 1
#     puts "calling block"
#     block.call
#     output_queue << x + y
#   end
# end

# 3.times do |i|
#   result_queue = Queue.new
#   input_queue << [i, 10 - i, proc { puts i }, result_queue]
#   puts "waiting for result"
#   puts "result: #{result_queue.pop}"
# end

class NeoThread
  # all calls execute the block in the one looping thread (using input queue)
  # calls are blocking (thanks to ouptut_queue.pop)
  # to make them non-blocking, output queue could just be returned (as a
  # promise) and caller would then call pop on it when needed
  def self.execute(&block)
    output_queue = Queue.new
    input_queue << [block, output_queue]
    output_queue.pop
  end

  def self.start
    return if @started
    @started = true

    @thread = Thread.new do
      loop do
        block, output_queue = input_queue.pop
        result = block.call
        output_queue << result
      end
    end
  end

  def self.stop
    @thread.stop if @thread
  end

  private

  def self.input_queue
    @input_queue ||= Queue.new
  end
end

puts "main thread: #{Thread.current}"

NeoThread.start

NeoThread.execute { puts "main scheduled for neo thread (#{Thread.current})"; sleep 1 }

threads = Array.new(3) do |i|
  Thread.new do
    puts "worker: #{i}, thread: #{Thread.current}"
    NeoThread.execute do
      puts "#{i} scheduled for neo thread (#{Thread.current})"
      sleep 1
    end
    puts "end worker: #{i}"
  end
end

threads.each(&:join)

puts "end main thread"