test.cr

fiber_count = 1
ready_scanline = Channel(UInt32 | Nil).new
available_lines = Channel(UInt32).new
finished = Channel(Nil).new

# Fill available
spawn do
  fiber_count.times do |i|
    available_lines.send(i.to_u32)
  end
end

spawn do
  1000.times do |row_num|
    puts "i: #{row_num}"
    working_line = available_lines.receive

    ready_scanline.send(working_line)
  end

  puts "Send finished nils"
  fiber_count.times { ready_scanline.send(nil)}
end

fiber_count.times do |fiber_id|
  spawn do
    loop do
      working_line = ready_scanline.receive

      if working_line.nil?
        puts "Finished #{fiber_id}"
        finished.send(nil)
        # Done processing
        break
      else
        puts "requeue: #{working_line}"

        # At the very end this blocks forever
        available_lines.send(working_line)
        puts "done requeue: #{working_line}"
      end
    end
  end
end

puts "Block until all are processed"
fiber_count.times {|i| finished.receive ; puts "Done #{i} received" }
puts "Done received"