# -*- coding: utf-8 -*- """ Copyright (c) 2008, appengine-utilities project All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: - Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. - Neither the name of the appengine-utilities project nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. """ # main python imports import datetime import pickle import random import __main__ # google appengine import from google.appengine.ext import db from google.appengine.api import memcache # settings DEFAULT_TIMEOUT = 3600 # cache expires after one hour (3600 sec) CLEAN_CHECK_PERCENT = 50 # 15% of all requests will clean the database MAX_HITS_TO_CLEAN = 100 # the maximum number of cache hits to clean on attempt class _AppEngineUtilities_Cache(db.Model): # It's up to the application to determine the format of their keys cachekey = db.StringProperty() createTime = db.DateTimeProperty(auto_now_add=True) timeout = db.DateTimeProperty() value = db.BlobProperty() class Cache(object): """ Cache is used for storing pregenerated output and/or objects in the Big Table datastore to minimize the amount of queries needed for page displays. The idea is that complex queries that generate the same results really should only be run once. Cache can be used to store pregenerated value made from queries (or other calls such as urlFetch()), or the query objects themselves. """ def __init__(self, clean_check_percent = CLEAN_CHECK_PERCENT, max_hits_to_clean = MAX_HITS_TO_CLEAN, default_timeout = DEFAULT_TIMEOUT): """ Initializer Args: clean_check_percent: how often cache initialization should run the cache cleanup max_hits_to_clean: maximum number of stale hits to clean default_timeout: default length a cache item is good for """ self.clean_check_percent = clean_check_percent self.max_hits_to_clean = max_hits_to_clean self.default_timeout = default_timeout if random.randint(1, 100) < self.clean_check_percent: self._clean_cache() if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheInitialized') def _clean_cache(self): """ _clean_cache is a routine that is run to find and delete cache items that are old. This helps keep the size of your over all datastore down. """ query = _AppEngineUtilities_Cache.all() query.filter('timeout < ', datetime.datetime.now()) results = query.fetch(self.max_hits_to_clean) db.delete(results) #for result in results: # result.delete() def _validate_key(self, key): if key == None: raise KeyError def _validate_value(self, value): if value == None: raise ValueError def _validate_timeout(self, timeout): if timeout == None: timeout = datetime.datetime.now() +\ datetime.timedelta(seconds=DEFAULT_TIMEOUT) if type(timeout) == type(1): timeout = datetime.datetime.now() + \ datetime.timedelta(seconds = timeout) if type(timeout) != datetime.datetime: raise TypeError if timeout < datetime.datetime.now(): raise ValueError return timeout def add(self, key = None, value = None, timeout = None): """ add adds an entry to the cache, if one does not already exist. """ self._validate_key(key) self._validate_value(value) timeout = self._validate_timeout(timeout) if key in self: raise KeyError cacheEntry = _AppEngineUtilities_Cache() cacheEntry.cachekey = key cacheEntry.value = pickle.dumps(value) cacheEntry.timeout = timeout # try to put the entry, if it fails silently pass # failures may happen due to timeouts, the datastore being read # only for maintenance or other applications. However, cache # not being able to write to the datastore should not # break the application try: cacheEntry.put() except: pass memcache_timeout = timeout - datetime.datetime.now() memcache.set('cache-'+key, value, int(memcache_timeout.seconds)) if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheAdded') def set(self, key = None, value = None, timeout = None): """ add adds an entry to the cache, overwriting an existing value if one already exists. """ self._validate_key(key) self._validate_value(value) timeout = self._validate_timeout(timeout) cacheEntry = self._read(key) if not cacheEntry: cacheEntry = _AppEngineUtilities_Cache() cacheEntry.cachekey = key cacheEntry.value = pickle.dumps(value) cacheEntry.timeout = timeout try: cacheEntry.put() except: pass memcache_timeout = timeout - datetime.datetime.now() memcache.set('cache-'+key, value, int(memcache_timeout.seconds)) if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheSet') def _read(self, key = None): """ _read returns a cache object determined by the key. It's set to private because it returns a db.Model object, and also does not handle the unpickling of objects making it not the best candidate for use. The special method __getitem__ is the preferred access method for cache data. """ query = _AppEngineUtilities_Cache.all() query.filter('cachekey', key) query.filter('timeout > ', datetime.datetime.now()) results = query.fetch(1) if len(results) is 0: return None return results[0] if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheReadFromDatastore') if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheRead') def delete(self, key = None): """ Deletes a cache object determined by the key. """ memcache.delete('cache-'+key) result = self._read(key) if result: if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheDeleted') result.delete() def get(self, key): """ get is used to return the cache value associated with the key passed. """ mc = memcache.get('cache-'+key) if mc: if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheReadFromMemcache') if 'AEU_Events' in __main__.__dict__: __main__.AEU_Events.fire_event('cacheRead') return mc result = self._read(key) if result: timeout = result.timeout - datetime.datetime.now() # print timeout.seconds memcache.set('cache-'+key, pickle.loads(result.value), int(timeout.seconds)) return pickle.loads(result.value) else: raise KeyError def get_many(self, keys): """ Returns a dict mapping each key in keys to its value. If the given key is missing, it will be missing from the response dict. """ dict = {} for key in keys: value = self.get(key) if value is not None: dict[key] = val return dict def __getitem__(self, key): """ __getitem__ is necessary for this object to emulate a container. """ return self.get(key) def __setitem__(self, key, value): """ __setitem__ is necessary for this object to emulate a container. """ return self.set(key, value) def __delitem__(self, key): """ Implement the 'del' keyword """ return self.delete(key) def __contains__(self, key): """ Implements "in" operator """ try: r = self.__getitem__(key) except KeyError: return False return True def has_key(self, keyname): """ Equivalent to k in a, use that form in new code """ return self.__contains__(keyname)