Package pyxmpp :: Module cache :: Class CacheSuite
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Class CacheSuite


Caching proxy for object retrieval and caching.

Object factories for other classes are registered in the Cache object and used to e.g. retrieve requested objects from network. They are called only when the requested object is not in the cache or is not fresh enough.

Objects are addressed using their class and a class dependant address. Eg. pyxmpp.jabber.disco.DiscoInfo objects are addressed using (pyxmpp.jabber.disco.DiscoInfo,(jid, node)) tuple.

Additionaly a state (freshness level) name may be provided when requesting an object. When the cached item state is "less fresh" then requested, then new object will be retrieved.

Following states are defined:


Method Summary
  __init__(self, max_items, default_freshness_period, default_expiration_period, default_purge_period)
Initialize a Cache object.
  register_fetcher(self, object_class, fetcher_class)
Register a fetcher class for an object class.
  request_object(self, object_class, address, state, object_handler, error_handler, timeout_handler, backup_state, timeout, freshness_period, expiration_period, purge_period)
Request an object of given class, with given address and state not worse than state.
  tick(self)
Do the regular cache maintenance.
  unregister_fetcher(self, object_class)
Unregister a fetcher class for an object class.

Instance Variable Summary
timedelta default_expiration_period: default expiration period (in seconds).
timedelta default_freshness_period: default freshness period (in seconds).
timedelta default_purge_period: default purge period (in seconds).
int max_items: maximum number of obejects of one class to store.
dict of (classobj, addr) -> Cache _caches: dictionary of per-class caches.
threading.RLock _lock: lock for thread safety.

Method Details

__init__(self, max_items, default_freshness_period=datetime.timedelta(0, 3600), default_expiration_period=datetime.timedelta(0, 43200), default_purge_period=datetime.timedelta(1))
(Constructor)

Initialize a Cache object.
Parameters:
max_items - maximum number of items to store.
           (type=number)
default_freshness_period - default freshness period (in seconds).
           (type=number)
default_expiration_period - default expiration period (in seconds).
           (type=number)
default_purge_period - default purge period (in seconds). When 0 then items are never purged because of their age.
           (type=number)

register_fetcher(self, object_class, fetcher_class)

Register a fetcher class for an object class.
Parameters:
object_class - class to be retrieved by the fetcher.
           (type=classobj)
fetcher_class - the fetcher class.
           (type=CacheFetcher based class)

request_object(self, object_class, address, state, object_handler, error_handler=None, timeout_handler=None, backup_state=None, timeout=None, freshness_period=None, expiration_period=None, purge_period=None)

Request an object of given class, with given address and state not worse than state. The object will be taken from cache if available, and created/fetched otherwise. The request is asynchronous -- this metod doesn't return the object directly, but the object_handler is called as soon as the object is available (this may be before request_object returns and may happen in other thread). On error the error_handler will be called, and on timeout -- the timeout_handler.
Parameters:
object_class - class (type) of the object requested.
           (type=classobj)
address - address of the object requested.
           (type=any hashable)
state - the worst acceptable object state. When 'new' then always a new object will be created/fetched. 'stale' will select any item available in cache.
           (type="new", "fresh", "old" or "stale")
object_handler - function to be called when object is available. It will be called with the following arguments: address, object and its state.
           (type=callable(address, value, state))
error_handler - function to be called on object retrieval error. It will be called with two arguments: requested address and additional error information (fetcher-specific, may be StanzaError for XMPP objects). If not given, then the object handler will be called with object set to None and state "error".
           (type=callable(address, error_data))
timeout_handler - function to be called on object retrieval timeout. It will be called with only one argument: the requested address. If not given, then the error_handler will be called instead, with error details set to None.
           (type=callable(address))
backup_state - when set and object in state state is not available in the cache and object retrieval failed then object with this state will also be looked-up in the cache and provided if available.
           (type="new", "fresh", "old" or "stale")
timeout - time interval after which retrieval of the object should be given up.
           (type=timedelta)
freshness_period - time interval after which the item created should become 'old'.
           (type=timedelta)
expiration_period - time interval after which the item created should become 'stale'.
           (type=timedelta)
purge_period - time interval after which the item created shuld be removed from the cache.
           (type=timedelta)

tick(self)

Do the regular cache maintenance.

Must be called from time to time for timeouts and cache old items purging to work.

unregister_fetcher(self, object_class)

Unregister a fetcher class for an object class.
Parameters:
object_class - class retrieved by the fetcher.
           (type=classobj)

Instance Variable Details

default_expiration_period

default expiration period (in seconds).
Type:
timedelta

default_freshness_period

default freshness period (in seconds).
Type:
timedelta

default_purge_period

default purge period (in seconds). When 0 then items are never purged because of their age.
Type:
timedelta

max_items

maximum number of obejects of one class to store.
Type:
int

_caches

dictionary of per-class caches.
Type:
dict of (classobj, addr) -> Cache

_lock

lock for thread safety.
Type:
threading.RLock