root / lib / cache.py @ bd6d1202
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# Copyright (C) 2011 Google Inc.
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301, USA.
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"""This module implements caching."""
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import time |
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from ganeti import locking |
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from ganeti import serializer |
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TIMESTAMP = "timestamp"
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TTL = "ttl"
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VALUE = "value"
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class CacheBase: |
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"""This is the base class for all caches.
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"""
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def __init__(self): |
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"""Base init method.
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"""
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def Store(self, key, value, ttl=0): |
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"""Stores key with value in the cache.
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@param key: The key to associate this cached value
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@param value: The value to cache
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@param ttl: TTL in seconds after when this entry is considered outdated
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@returns: L{True} on success, L{False} on failure
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"""
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raise NotImplementedError |
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def GetMulti(self, keys): |
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"""Retrieve multiple values from the cache.
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@param keys: The keys to retrieve
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@returns: The list of values
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"""
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raise NotImplementedError |
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def Get(self, key): |
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"""Retrieve the value from the cache.
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@param key: The key to retrieve
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@returns: The value or L{None} if not found
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"""
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raise NotImplementedError |
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def Invalidate(self, keys): |
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"""Invalidate given keys.
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@param keys: The list of keys to invalidate
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@returns: L{True} on success, L{False} otherwise
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"""
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raise NotImplementedError |
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def Flush(self): |
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"""Invalidates all of the keys and flushes the cache.
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"""
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raise NotImplementedError |
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def ResetState(self): |
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"""Used to reset the state of the cache.
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This can be used to reinstantiate connection or any other state refresh
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"""
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def Cleanup(self): |
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"""Cleanup the cache from expired entries.
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"""
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class SimpleCache(CacheBase): |
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"""Implements a very simple, dict base cache.
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"""
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CLEANUP_ROUND = 1800
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_LOCK = "lock"
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def __init__(self, _time_fn=time.time): |
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"""Initialize this class.
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@param _time_fn: Function used to return time (unittest only)
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"""
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CacheBase.__init__(self)
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self._time_fn = _time_fn
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self.cache = {}
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self.lock = locking.SharedLock("SimpleCache") |
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self.last_cleanup = self._time_fn() |
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def _UnlockedCleanup(self): |
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"""Does cleanup of the cache.
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"""
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check_time = self._time_fn()
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if (self.last_cleanup + self.CLEANUP_ROUND) <= check_time: |
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keys = [] |
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for key, value in self.cache.items(): |
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if not value[TTL]: |
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continue
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expired = value[TIMESTAMP] + value[TTL] |
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if expired < check_time:
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keys.append(key) |
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self._UnlockedInvalidate(keys)
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self.last_cleanup = check_time
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@locking.ssynchronized(_LOCK)
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def Cleanup(self): |
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"""Cleanup our cache.
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"""
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self._UnlockedCleanup()
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@locking.ssynchronized(_LOCK)
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def Store(self, key, value, ttl=0): |
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"""Stores a value at key in the cache.
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See L{CacheBase.Store} for parameter description
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"""
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assert ttl >= 0 |
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self._UnlockedCleanup()
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val = serializer.Dump(value) |
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cache_val = { |
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TIMESTAMP: self._time_fn(),
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TTL: ttl, |
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VALUE: val |
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} |
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self.cache[key] = cache_val
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return True |
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@locking.ssynchronized(_LOCK, shared=1) |
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def GetMulti(self, keys): |
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"""Retrieve the values of keys from cache.
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See L{CacheBase.GetMulti} for parameter description
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"""
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return [self._ExtractValue(key) for key in keys] |
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@locking.ssynchronized(_LOCK, shared=1) |
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def Get(self, key): |
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"""Retrieve the value of key from cache.
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See L{CacheBase.Get} for parameter description
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"""
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return self._ExtractValue(key) |
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@locking.ssynchronized(_LOCK)
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def Invalidate(self, keys): |
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"""Invalidates value for keys in cache.
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See L{CacheBase.Invalidate} for parameter description
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"""
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return self._UnlockedInvalidate(keys) |
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@locking.ssynchronized(_LOCK)
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def Flush(self): |
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"""Invalidates all keys and values in cache.
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See L{CacheBase.Flush} for parameter description
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"""
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self.cache.clear()
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self.last_cleanup = self._time_fn() |
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def _UnlockedInvalidate(self, keys): |
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"""Invalidate keys in cache.
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This is the unlocked version, see L{Invalidate} for parameter description
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"""
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for key in keys: |
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self.cache.pop(key, None) |
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return True |
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def _ExtractValue(self, key): |
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"""Extracts just the value for a key.
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This method is taking care if the value did not expire ans returns it
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@param key: The key to look for
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@returns: The value if key is not expired, L{None} otherwise
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"""
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try:
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cache_val = self.cache[key]
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except KeyError: |
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return None |
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else:
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if cache_val[TTL] == 0: |
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return serializer.Load(cache_val[VALUE])
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else:
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expired = cache_val[TIMESTAMP] + cache_val[TTL] |
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if self._time_fn() <= expired: |
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return serializer.Load(cache_val[VALUE])
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else:
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return None |