diff options
Diffstat (limited to 'src/cachetools/ttl.py')
-rw-r--r-- | src/cachetools/ttl.py | 207 |
1 files changed, 207 insertions, 0 deletions
diff --git a/src/cachetools/ttl.py b/src/cachetools/ttl.py new file mode 100644 index 0000000..eef8877 --- /dev/null +++ b/src/cachetools/ttl.py @@ -0,0 +1,207 @@ +import collections +import time + +from .cache import Cache + + +class _Link: + + __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: + 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().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: + raise KeyError("%s is empty" % type(self).__name__) from None + else: + return (key, self.pop(key)) + + def __getlink(self, key): + value = self.__links[key] + self.__links.move_to_end(key) + return value |