File size: 2,205 Bytes
895e804 1bfc3f0 895e804 1bfc3f0 895e804 1bfc3f0 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 | """Small per-instance LRU caches; no global references to fitted codecs."""
from collections import OrderedDict
from collections.abc import MutableMapping
from threading import RLock
def cached_prefix_state(key, cache, initial, advance):
"""Extend a cached parent prefix, replaying only when it was evicted."""
if not key:
return initial
missing = object()
state = cache.get(key, missing)
if state is not missing:
return state
parent = key[:-1]
state = cache.get(parent, missing)
if state is missing:
state = initial
for token in parent:
state = advance(state, token)
if state is None:
break
cache[parent] = state
if state is not None:
state = advance(state, key[-1])
cache[key] = state
return state
class BoundedCache(MutableMapping):
"""Evict least-recently-used entries above a fixed capacity."""
def __init__(self, capacity):
if type(capacity) is not int or capacity < 1:
raise ValueError("cache capacity must be a positive integer")
self.capacity = capacity
self._items = OrderedDict()
self._lock = RLock()
def __getitem__(self, key):
with self._lock:
value = self._items[key]
self._items.move_to_end(key)
return value
def __setitem__(self, key, value):
with self._lock:
self._items[key] = value
self._items.move_to_end(key)
while len(self._items) > self.capacity:
self._items.popitem(last=False)
def __delitem__(self, key):
with self._lock:
del self._items[key]
def __iter__(self):
with self._lock:
return iter(tuple(self._items))
def __len__(self):
with self._lock:
return len(self._items)
def reserve(self, capacity):
"""Raise the capacity so callers with a known working set stop thrashing."""
if type(capacity) is not int or capacity < 1:
raise ValueError("cache capacity must be a positive integer")
with self._lock:
self.capacity = max(self.capacity, capacity)
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