diff options
| -rw-r--r-- | repoze/lru/__init__.py | 26 |
1 files changed, 17 insertions, 9 deletions
diff --git a/repoze/lru/__init__.py b/repoze/lru/__init__.py index d3aa5ba..0fb7029 100644 --- a/repoze/lru/__init__.py +++ b/repoze/lru/__init__.py @@ -7,13 +7,18 @@ try: except NameError: # pragma: no cover pass -_marker = object() +_MARKER = object() class LRUCache(object): + """ Implements a pseudo-LRU algorithm (CLOCK) + + The Clock algorithm is not kept strictly to improve performance, e.g. to + allow get() and invalidate() to work without acquiring the lock. + """ def __init__(self, size): - """ Implements a psueudo-LRU algorithm (CLOCK) """ + size = int(size) if size < 1: - raise ValueError('size must be >1') + raise ValueError('size must be >0') self.size = size self.lock = threading.Lock() self.hand = 0 @@ -24,23 +29,25 @@ class LRUCache(object): self.clear() def clear(self): + """Remove all entries from the cache""" self.lock.acquire() try: # If really clear()ing a full cache, clean up self.data first to # give garbage collection a chance to reduce memorey usage. - # Instantiating "[_marker] * size" will temporarily have 2 lists + # Instantiating "[_MARKER] * size" will temporarily have 2 lists # in memory -> high peak memory usage for tiny amount of time. # With self.data already clear, that peak should not exceed what # we normally use. self.data = {} size = self.size - self.clock_keys = [_marker] * size + self.clock_keys = [_MARKER] * size self.clock_refs = [False] * size self.hand = 0 finally: self.lock.release() def get(self, key, default=None): + """Return value for key, if not in cache, return default""" try: pos, val = self.data[key] except KeyError: @@ -48,7 +55,8 @@ class LRUCache(object): self.clock_refs[pos] = True return val - def put(self, key, val, _marker=_marker): + def put(self, key, val): + """Add key to the cache with value val""" # These do not change or they are just references, no need for locking. maxpos = self.maxpos clock_refs = self.clock_refs @@ -105,8 +113,8 @@ class LRUCache(object): def invalidate(self, key): """Remove key from the cache""" # pop with default arg will not raise KeyError - entry = self.data.pop(key, _marker) - if entry is not _marker: + entry = self.data.pop(key, _MARKER) + if entry is not _MARKER: # We have no lock, but worst thing that can happen is that we # set another key's entry to False. self.clock_refs[entry[0]] = False @@ -121,7 +129,7 @@ class lru_cache(object): def __call__(self, f): cache = self.cache - marker = _marker + marker = _MARKER def lru_cached(*arg): val = cache.get(arg, marker) if val is marker: |