Line by line explanation of Ruby 3 Ractor – worker pool implementation

# This example computes if the given numbers is a prime number or not, using 10 parallel workers. 

# to make `num.prime?` possible.
require 'prime'

# this ractor will keep listening to the sent messages, and yield them to whomever want to take the value.
pipe = Ractor.new do
  loop do
    Ractor.yield Ractor.receive
  end
end

# Let's check the prime numbers from 1 upto 1000
N = 1000
# we'll use 10 workers to do this work.
RN = 10
# worker ractors initialization.
# each worker ractor takes pipe as its sharable object (Ractor has some synchronization mechanism according to [this doc](https://github.com/ruby/ruby/blob/master/doc/ractor.md#shareable-objects)) 
# then, each worker Ractor reads the input through the pipe (multiplexing) to utilize 10 workers
workers = (1..RN).map.with_index do |i|
  Ractor.new pipe, i do |pipe, i|
    # Ractor#take is a blocking call, and waits till pipe yields something
    while n = pipe.take
      # Worker, then in turn, computes something (expensive :) and yields to whomever willing to listen to this ractor
      Ractor.yield ["worker ##{i}}", n, n.prime?]
    end
  end
end

# sending 1000 numbers to the pipe, worker ractors are ready to consume by now.
(1..N).each{|i|
  pipe << i
}

# main process (main process itself is a running Ractor) calls
# Ractor#select, which can listen to a list of ractors
# because it's called (1..N) times, it'll hit all of the computed values by the time pp prints them.
pp (1..N).map{
  _r, (wid, n, b) = Ractor.select(*workers)
  [wid, n, b]
}.sort_by{|(wid, n, b)| n}