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Source code for kivy.cache

'''
Cache manager
=============

The cache manager can be used to store python objects attached to a unique
key. The cache can be controlled in two ways: with a object limit or a
timeout.

For example, we can create a new cache with a limit of 10 objects and a
timeout of 5 seconds::

    # register a new Cache
    Cache.register('mycache', limit=10, timeout=5)

    # create an object + id
    key = 'objectid'
    instance = Label(text=text)
    Cache.append('mycache', key, instance)

    # retrieve the cached object
    instance = Cache.get('mycache', key)

If the instance is NULL, the cache may have trashed it because you've
not used the label for 5 seconds and you've reach the limit.
'''

from os import environ
from kivy.logger import Logger
from kivy.clock import Clock

__all__ = ('Cache', )


[docs]class Cache(object): '''See module documentation for more information. ''' _categories = {} _objects = {}
[docs] @staticmethod def register(category, limit=None, timeout=None): '''Register a new category in the cache with the specified limit. :Parameters: `category`: str Identifier of the category. `limit`: int (optional) Maximum number of objects allowed in the cache. If None, no limit is applied. `timeout`: double (optional) Time after which to delete the object if it has not been used. If None, no timeout is applied. ''' Cache._categories[category] = { 'limit': limit, 'timeout': timeout} Cache._objects[category] = {} Logger.debug( 'Cache: register <%s> with limit=%s, timeout=%s' % (category, str(limit), str(timeout)))
[docs] @staticmethod def append(category, key, obj, timeout=None): '''Add a new object to the cache. :Parameters: `category`: str Identifier of the category. `key`: str Unique identifier of the object to store. `obj`: object Object to store in cache. `timeout`: double (optional) Time after which to delete the object if it has not been used. If None, no timeout is applied. ''' # check whether obj should not be cached first if getattr(obj, '_nocache', False): return try: cat = Cache._categories[category] except KeyError: Logger.warning('Cache: category <%s> does not exist' % category) return timeout = timeout or cat['timeout'] limit = cat['limit'] if limit is not None and len(Cache._objects[category]) >= limit: Cache._purge_oldest(category) Cache._objects[category][key] = { 'object': obj, 'timeout': timeout, 'lastaccess': Clock.get_time(), 'timestamp': Clock.get_time()}
[docs] @staticmethod def get(category, key, default=None): '''Get a object from the cache. :Parameters: `category`: str Identifier of the category. `key`: str Unique identifier of the object in the store. `default`: anything, defaults to None Default value to be returned if the key is not found. ''' try: Cache._objects[category][key]['lastaccess'] = Clock.get_time() return Cache._objects[category][key]['object'] except Exception: return default
[docs] @staticmethod def get_timestamp(category, key, default=None): '''Get the object timestamp in the cache. :Parameters: `category`: str Identifier of the category. `key`: str Unique identifier of the object in the store. `default`: anything, defaults to None Default value to be returned if the key is not found. ''' try: return Cache._objects[category][key]['timestamp'] except Exception: return default
[docs] @staticmethod def get_lastaccess(category, key, default=None): '''Get the objects last access time in the cache. :Parameters: `category`: str Identifier of the category. `key`: str Unique identifier of the object in the store. `default`: anything, defaults to None Default value to be returned if the key is not found. ''' try: return Cache._objects[category][key]['lastaccess'] except Exception: return default
[docs] @staticmethod def remove(category, key=None): '''Purge the cache. :Parameters: `category`: str Identifier of the category. `key`: str (optional) Unique identifier of the object in the store. If this argument is not supplied, the entire category will be purged. ''' try: if key is not None: del Cache._objects[category][key] else: Cache._objects[category] = {} except Exception: pass
@staticmethod def _purge_oldest(category, maxpurge=1): print('PURGE', category) import heapq time = Clock.get_time() heap_list = [] for key in Cache._objects[category]: obj = Cache._objects[category][key] if obj['lastaccess'] == obj['timestamp'] == time: continue heapq.heappush(heap_list, (obj['lastaccess'], key)) print('<<<', obj['lastaccess']) n = 0 while n <= maxpurge: try: n += 1 lastaccess, key = heapq.heappop(heap_list) print(n, '=>', key, lastaccess, Clock.get_time()) except Exception: return Cache.remove(category, key) @staticmethod def _purge_by_timeout(dt): curtime = Clock.get_time() for category in Cache._objects: if category not in Cache._categories: continue timeout = Cache._categories[category]['timeout'] if timeout is not None and dt > timeout: # XXX got a lag ! that may be because the frame take lot of # time to draw. and the timeout is not adapted to the current # framerate. So, increase the timeout by two. # ie: if the timeout is 1 sec, and framerate go to 0.7, newly # object added will be automatically trashed. timeout *= 2 Cache._categories[category]['timeout'] = timeout continue for key in list(Cache._objects[category].keys())[:]: lastaccess = Cache._objects[category][key]['lastaccess'] objtimeout = Cache._objects[category][key]['timeout'] # take the object timeout if available if objtimeout is not None: timeout = objtimeout # no timeout, cancel if timeout is None: continue if curtime - lastaccess > timeout: Cache.remove(category, key)
[docs] @staticmethod def print_usage(): '''Print the cache usage to the console.''' print('Cache usage :') for category in Cache._categories: print(' * %s : %d / %s, timeout=%s' % ( category.capitalize(), len(Cache._objects[category]), str(Cache._categories[category]['limit']), str(Cache._categories[category]['timeout'])))
if 'KIVY_DOC_INCLUDE' not in environ: # install the schedule clock for purging Clock.schedule_interval(Cache._purge_by_timeout, 1)