gistfile1.py

import threading
import time

def cool_function():
  print "Herro!"
  
if __name__ == "__main__":
  thread_limit = 5

  while True:
    while threading.activeCount() >= thread_limit + 1: # (you add one because there is always at least one thread running (the main thread))
      # This is a great place to update a progress bar or something
      time.sleep(0.1)

    threading.Thread(target=cool_function).start()