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