import collections import time from .cache import Cache class _Link(object): __slots__ = ('key', 'expire', 'next', 'prev') def __init__(self, key=None, expire=None): self.key = key self.expire = expire def __reduce__(self): return _Link, (self.key, self.expire) def unlink(self): next = self.next prev = self.prev prev.next = next next.prev = prev class _Timer(object): def __init__(self, timer): self.__timer = timer self.__nesting = 0 def __call__(self): if self.__nesting == 0: return self.__timer() else: return self.__time def __enter__(self): if self.__nesting == 0: self.__time = time = self.__timer() else: time = self.__time self.__nesting += 1 return time def __exit__(self, *exc): self.__nesting -= 1 def __reduce__(self): return _Timer, (self.__timer,) def __getattr__(self, name): return getattr(self.__timer, name) class TTLCache(Cache): """LRU Cache implementation with per-item time-to-live (TTL) value.""" def __init__(self, maxsize, ttl, timer=time.monotonic, getsizeof=None): Cache.__init__(self, maxsize, getsizeof) self.__root = root = _Link() root.prev = root.next = root self.__links = collections.OrderedDict() self.__timer = _Timer(timer) self.__ttl = ttl def __contains__(self, key): try: link = self.__links[key] # no reordering except KeyError: return False else: return not (link.expire < self.__timer()) def __getitem__(self, key, cache_getitem=Cache.__getitem__): try: link = self.__getlink(key) except KeyError: expired = False else: expired = link.expire < self.__timer() if expired: return self.__missing__(key) else: return cache_getitem(self, key) def __setitem__(self, key, value, cache_setitem=Cache.__setitem__): with self.__timer as time: self.expire(time) cache_setitem(self, key, value) try: link = self.__getlink(key) except KeyError: self.__links[key] = link = _Link(key) else: link.unlink() link.expire = time + self.__ttl link.next = root = self.__root link.prev = prev = root.prev prev.next = root.prev = link def __delitem__(self, key, cache_delitem=Cache.__delitem__): cache_delitem(self, key) link = self.__links.pop(key) link.unlink() if link.expire < self.__timer(): raise KeyError(key) def __iter__(self): root = self.__root curr = root.next while curr is not root: # "freeze" time for iterator access with self.__timer as time: if not (curr.expire < time): yield curr.key curr = curr.next def __len__(self): root = self.__root curr = root.next time = self.__timer() count = len(self.__links) while curr is not root and curr.expire < time: count -= 1 curr = curr.next return count def __setstate__(self, state): self.__dict__.update(state) root = self.__root root.prev = root.next = root for link in sorted(self.__links.values(), key=lambda obj: obj.expire): link.next = root link.prev = prev = root.prev prev.next = root.prev = link self.expire(self.__timer()) def __repr__(self, cache_repr=Cache.__repr__): with self.__timer as time: self.expire(time) return cache_repr(self) @property def currsize(self): with self.__timer as time: self.expire(time) return super(TTLCache, self).currsize @property def timer(self): """The timer function used by the cache.""" return self.__timer @property def ttl(self): """The time-to-live value of the cache's items.""" return self.__ttl def expire(self, time=None): """Remove expired items from the cache.""" if time is None: time = self.__timer() root = self.__root curr = root.next links = self.__links cache_delitem = Cache.__delitem__ while curr is not root and curr.expire < time: cache_delitem(self, curr.key) del links[curr.key] next = curr.next curr.unlink() curr = next def clear(self): with self.__timer as time: self.expire(time) Cache.clear(self) def get(self, *args, **kwargs): with self.__timer: return Cache.get(self, *args, **kwargs) def pop(self, *args, **kwargs): with self.__timer: return Cache.pop(self, *args, **kwargs) def setdefault(self, *args, **kwargs): with self.__timer: return Cache.setdefault(self, *args, **kwargs) def popitem(self): """Remove and return the `(key, value)` pair least recently used that has not already expired. """ with self.__timer as time: self.expire(time) try: key = next(iter(self.__links)) except StopIteration: msg = '%s is empty' % self.__class__.__name__ raise KeyError(msg) from None else: return (key, self.pop(key)) def __getlink(self, key): value = self.__links[key] self.__links.move_to_end(key) return value