forking and waiting with Ruby

forking_and_waiting.rb

pids = []
[0, 1, 2].each do |i|
  pids << fork do
    sleep 5 - i
    puts "Hi from #{i}\n"
  end
end

puts "done forking" # note: if you >> this file to another file, you will need $stdout.flush to ensure proper write ordering
pids.each { |pid| Process.wait pid }
puts "done with everything running"

#=> done forking
#=> Hi from 2
#=> Hi from 1
#=> Hi from 0
#=> done with everything running

more_forking_and_waiting.rb

pids = []
[0, 1, 2].each do |i|
  pids << fork do
    sleep 5 if i == 2
    puts "Hi from #{i}\n"
  end
end

puts "done forking" # note: if you >> this file to another file, you will need $stdout.flush to ensure proper write ordering
pids.each { |pid| Process.wait pid }
sleep 4
puts "done with everything running"

#=> Hi from 0 (immedate)
#=> Hi from 1 (immedate)
#=> done forking (immedate)
#=> Hi from 2 (5 seconds)
#=> done with everything running  (4 seconds after 2 finishes)