151 lines
4.2 KiB
Python
151 lines
4.2 KiB
Python
#!/usr/bin/python
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# -*- coding: utf-8 -*-
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#
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# Copyright 2015 clowwindy
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# 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, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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from __future__ import absolute_import, division, print_function, \
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with_statement
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import collections
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import logging
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import time
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# this LRUCache is optimized for concurrency, not QPS
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# n: concurrency, keys stored in the cache
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# m: visits not timed out, proportional to QPS * timeout
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# get & set is O(1), not O(n). thus we can support very large n
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# TODO: if timeout or QPS is too large, then this cache is not very efficient,
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# as sweep() causes long pause
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class LRUCache(collections.MutableMapping):
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"""This class is not thread safe"""
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def __init__(self, timeout=60, close_callback=None, *args, **kwargs):
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self.timeout = timeout
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self.close_callback = close_callback
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self._store = {}
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self._time_to_keys = collections.defaultdict(list)
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self._keys_to_last_time = {}
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self._last_visits = collections.deque()
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self._closed_values = set()
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self.update(dict(*args, **kwargs)) # use the free update to set keys
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def __getitem__(self, key):
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# O(1)
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t = time.time()
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self._keys_to_last_time[key] = t
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self._time_to_keys[t].append(key)
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self._last_visits.append(t)
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return self._store[key]
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def __setitem__(self, key, value):
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# O(1)
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t = time.time()
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self._keys_to_last_time[key] = t
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self._store[key] = value
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self._time_to_keys[t].append(key)
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self._last_visits.append(t)
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def __delitem__(self, key):
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# O(1)
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del self._store[key]
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del self._keys_to_last_time[key]
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def __iter__(self):
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return iter(self._store)
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def __len__(self):
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return len(self._store)
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def sweep(self):
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# O(m)
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now = time.time()
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c = 0
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while len(self._last_visits) > 0:
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least = self._last_visits[0]
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if now - least <= self.timeout:
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break
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if self.close_callback is not None:
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for key in self._time_to_keys[least]:
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if key in self._store:
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if now - self._keys_to_last_time[key] > self.timeout:
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value = self._store[key]
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if value not in self._closed_values:
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self.close_callback(value)
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self._closed_values.add(value)
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self._last_visits.popleft()
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for key in self._time_to_keys[least]:
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if key in self._store:
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if now - self._keys_to_last_time[key] > self.timeout:
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del self._store[key]
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del self._keys_to_last_time[key]
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c += 1
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del self._time_to_keys[least]
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if c:
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self._closed_values.clear()
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logging.debug('%d keys swept' % c)
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def test():
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c = LRUCache(timeout=0.3)
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c['a'] = 1
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assert c['a'] == 1
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time.sleep(0.5)
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c.sweep()
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assert 'a' not in c
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c['a'] = 2
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c['b'] = 3
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time.sleep(0.2)
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c.sweep()
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assert c['a'] == 2
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assert c['b'] == 3
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time.sleep(0.2)
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c.sweep()
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c['b']
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time.sleep(0.2)
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c.sweep()
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assert 'a' not in c
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assert c['b'] == 3
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time.sleep(0.5)
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c.sweep()
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assert 'a' not in c
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assert 'b' not in c
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global close_cb_called
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close_cb_called = False
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def close_cb(t):
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global close_cb_called
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assert not close_cb_called
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close_cb_called = True
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c = LRUCache(timeout=0.1, close_callback=close_cb)
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c['s'] = 1
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c['s']
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time.sleep(0.1)
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c['s']
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time.sleep(0.3)
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c.sweep()
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if __name__ == '__main__':
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test()
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