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115 lines
3.5 KiB
Python
115 lines
3.5 KiB
Python
# copyright 2003-2011 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
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# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
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#
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# This file is part of logilab-common.
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#
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# logilab-common is free software: you can redistribute it and/or modify it under
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# the terms of the GNU Lesser General Public License as published by the Free
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# Software Foundation, either version 2.1 of the License, or (at your option) any
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# later version.
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#
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# logilab-common is distributed in the hope that it will be useful, but WITHOUT
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# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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# FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
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# details.
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#
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# You should have received a copy of the GNU Lesser General Public License along
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# with logilab-common. If not, see <http://www.gnu.org/licenses/>.
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"""Cache module, with a least recently used algorithm for the management of the
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deletion of entries.
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"""
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__docformat__ = "restructuredtext en"
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from threading import Lock
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from logilab.common.decorators import locked
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_marker = object()
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class Cache(dict):
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"""A dictionary like cache.
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inv:
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len(self._usage) <= self.size
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len(self.data) <= self.size
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"""
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def __init__(self, size=100):
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""" Warning : Cache.__init__() != dict.__init__().
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Constructor does not take any arguments beside size.
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"""
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assert size >= 0, 'cache size must be >= 0 (0 meaning no caching)'
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self.size = size
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self._usage = []
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self._lock = Lock()
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super(Cache, self).__init__()
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def _acquire(self):
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self._lock.acquire()
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def _release(self):
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self._lock.release()
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def _update_usage(self, key):
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if not self._usage:
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self._usage.append(key)
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elif self._usage[-1] != key:
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try:
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self._usage.remove(key)
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except ValueError:
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# we are inserting a new key
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# check the size of the dictionary
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# and remove the oldest item in the cache
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if self.size and len(self._usage) >= self.size:
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super(Cache, self).__delitem__(self._usage[0])
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del self._usage[0]
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self._usage.append(key)
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else:
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pass # key is already the most recently used key
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def __getitem__(self, key):
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value = super(Cache, self).__getitem__(key)
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self._update_usage(key)
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return value
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__getitem__ = locked(_acquire, _release)(__getitem__)
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def __setitem__(self, key, item):
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# Just make sure that size > 0 before inserting a new item in the cache
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if self.size > 0:
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super(Cache, self).__setitem__(key, item)
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self._update_usage(key)
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__setitem__ = locked(_acquire, _release)(__setitem__)
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def __delitem__(self, key):
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super(Cache, self).__delitem__(key)
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self._usage.remove(key)
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__delitem__ = locked(_acquire, _release)(__delitem__)
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def clear(self):
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super(Cache, self).clear()
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self._usage = []
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clear = locked(_acquire, _release)(clear)
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def pop(self, key, default=_marker):
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if key in self:
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self._usage.remove(key)
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#if default is _marker:
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# return super(Cache, self).pop(key)
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return super(Cache, self).pop(key, default)
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pop = locked(_acquire, _release)(pop)
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def popitem(self):
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raise NotImplementedError()
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def setdefault(self, key, default=None):
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raise NotImplementedError()
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def update(self, other):
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raise NotImplementedError()
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