Programming Ruby 3.2 (5th Edition): B1.0 page 205, Only then do we create

@noelrappin

page 205, paragraph after the code, line 2 :

then blocks at Ractor.receive. Only then do we create the reading ractor

Because of “Only then” I thought that creating the second Ractor could only take place when the first is waiting on receive. But the trace shows that both Ractors are created, then the blocks are scheduled.

On page 204 (par. 5, code for one, line 1) I liked “Moving down the file”, for a possible replacement of “Only then”.

Having said that, it’s impressive to see the reader sending several times without waiting for a take.

def displayWord(p_word)
    p_word.nil? ? "^nil^" : "|#{p_word}|"
end
    
puts "*** (main) about to create counter"
counter = Ractor.new(name: "counter") do
  puts ">>> ccccc in counter block"
  result = Hash.new(0)
  while (word = Ractor.receive)
    puts "ccccc in counter received word=#{displayWord(word)}"
    result[word] += 1
    puts "ccccc looping"
  end
  puts "ccccc in counter while ended word=#{displayWord(word)}"
  result
end

puts "*** (main) about to create reader"
Ractor.new(counter, name: "reader") do |counter|
  puts ">>> rrrrr in reader block"
  File.foreach("testfile") do |line|
    puts "rrrrr line=#{line}"
    line.scan(/\w+/) do |word|
      puts "rrrrr about to send word=#{displayWord(word)}"
      counter.send(word.downcase)
      puts "rrrrr after send"
    end
  end
  puts "rrrrr about to send nil"
  counter.send(nil)
end

puts "*** (main) about to take counter"
counts = counter.take
counts.keys.sort.each { |k| print "#{k}:#{counts[k]} " }
puts

% ruby -w ractor_word_count_flipped.rb 
*** (main) about to create counter
<internal ... experimental ...
*** (main) about to create reader
*** (main) about to take counter
>>> ccccc in counter block
>>> rrrrr in reader block
rrrrr line=This is line one
rrrrr about to send word=|This|
rrrrr after send
rrrrr about to send word=|is|
rrrrr after send
rrrrr about to send word=|line|
ccccc in counter received word=|this|
...