''

def __init__(self, db, threshold=5, threshold_prune=60):

    self.db = db
    self.threshold = threshold
    self.threshold_prune = threshold_prune
    self.cache = {}
    class Locks:
        checkin = threading.Lock()
        checkout = threading.Lock()
    self.locks = Locks()
    self.pruner = threading.Thread(target=self.prune)
    self.pruner.setDaemon(True)
    self.pruner.start()
