old_contents: import time, gevent
  
  seen = None
  
  def used(url, http_pool):
      __patch()
      seen[(url, http_pool)] = time.time()
      
  def __patch():
      global seen
      if seen is None:
          seen = {}
          gevent.spawn(clean)
          
  def clean():
      while True:
          for k, last_seen in seen.items:
              if time.time()-last_seen < 0.3:
                  continue
              
              url, pool = k
              pool.request(url, 'GET', headers = {'Connection':'close'})
              
                  
  
new_contents: import time, gevent
  
  seen = None
  
  def used(url, http_pool):
      __patch()
      seen[(url, http_pool)] = time.time()
      
  def __patch():
      global seen
      if seen is None:
          seen = {}
          gevent.spawn(clean)
          
  def clean():
      while True:
          for k, last_seen in seen.items:
              if time.time()-last_seen < 0.3:
                  continue
              
              url, pool = k
              pool.request(url, 'GET', headers = {'Connection':'close'})
          gevent.sleep(0.3)
              
                  
  
subject: Add a pause.