naive multithreaded catastrophic backtracking

gistfile1.rb

p        = /\A(aa|aab?)+\Z/
@counter = 0
s        = ""
t        = []
64.times { t << Thread.fork { puts "start" }; t.last.join }

while s.length < 200
  i = s.length % t.size
  t[i].join
  t[i] = Thread.fork(s.dup) do |s|
    if s =~ p
      puts "+ #{@counter += 1}"
    else
      puts "  #{@counter}"
    end
  end
  s    += "a"
end

puts "\nFINAL RESULT: #{counter}"