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# -*- coding: utf-8 -*-
# Copyright 2015 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
class LruCache(object):
"""Least-recently-used cache."""
# TODO(mjark) Add mutex for linked list for thread safety.
def __init__(self, max_size):
cache = {}
list_root = []
list_root[:] = [list_root, list_root, None, None]
PREV, NEXT, KEY, VALUE = 0, 1, 2, 3
def add_node(key, value):
prev_node = list_root
next_node = prev_node[NEXT]
node = [prev_node, next_node, key, value]
prev_node[NEXT] = node
next_node[PREV] = node
cache[key] = node
def move_node_to_front(node):
prev_node = node[PREV]
next_node = node[NEXT]
prev_node[NEXT] = next_node
next_node[PREV] = prev_node
prev_node = list_root
next_node = prev_node[NEXT]
node[PREV] = prev_node
node[NEXT] = next_node
prev_node[NEXT] = node
next_node[PREV] = node
def delete_node(node):
prev_node = node[PREV]
next_node = node[NEXT]
prev_node[NEXT] = next_node
next_node[PREV] = prev_node
cache.pop(node[KEY], None)
def cache_get(key, default=None):
node = cache.get(key, None)
if node is not None:
move_node_to_front(node)
return node[VALUE]
else:
return default
def cache_set(key, value):
node = cache.get(key, None)
if node is not None:
move_node_to_front(node)
node[VALUE] = value
else:
add_node(key, value)
if len(cache) > max_size:
delete_node(list_root[PREV])
def cache_set_default(key, value):
node = cache.get(key, None)
if node is not None:
return node[VALUE]
else:
add_node(key, value)
if len(cache) > max_size:
delete_node(list_root[PREV])
return value
def cache_pop(key, default=None):
node = cache.get(key, None)
if node:
delete_node(node)
return node[VALUE]
else:
return default
def cache_len():
return len(cache)
self.sentinel = object()
self.get = cache_get
self.set = cache_set
self.setdefault = cache_set_default
self.pop = cache_pop
self.len = cache_len
def __getitem__(self, key):
result = self.get(key, self.sentinel)
if result is self.sentinel:
raise KeyError()
else:
return result
def __setitem__(self, key, value):
self.set(key, value)
def __delitem__(self, key, value):
result = self.pop(key, self.sentinel)
if result is self.sentinel:
raise KeyError()
def __len__(self):
return self.len()
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