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#
# (C) Copyright 2003-2010 Jacek Konieczny <jajcus@jajcus.net>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License Version
# 2.1 as published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this program; if not, write to the Free Software
# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
#
"""Dictionary with item expiration."""
__docformat__="restructuredtext en"
import time
import threading
__all__ = ['ExpiringDictionary']
sentinel = object()
class ExpiringDictionary(dict):
"""An extension to standard Python dictionary objects which implements item
expiration.
Each item in ExpiringDictionary has its expiration time assigned, after
which the item is removed from the mapping.
:Ivariables:
- `_timeouts`: a dictionary with timeout values and timeout callback for
stored objects.
- `_default_timeout`: the default timeout value (in seconds from now).
- `_lock`: access synchronization lock.
:Types:
- `_timeouts`: `dict`
- `_default_timeout`: `int`
- `_lock`: `threading.RLock`"""
__slots__=['_timeouts','_default_timeout','_lock']
def __init__(self,default_timeout=300):
"""Initialize an `ExpiringDictionary` object.
:Parameters:
- `default_timeout`: default timeout value for stored objects.
:Types:
- `default_timeout`: `int`"""
dict.__init__(self)
self._timeouts={}
self._default_timeout=default_timeout
self._lock=threading.RLock()
def __delitem__(self,key):
self._lock.acquire()
try:
del self._timeouts[key]
return dict.__delitem__(self,key)
finally:
self._lock.release()
def __getitem__(self,key):
self._lock.acquire()
try:
self._expire_item(key)
return dict.__getitem__(self,key)
finally:
self._lock.release()
def pop(self,key,default=sentinel):
self._lock.acquire()
try:
self._expire_item(key)
del self._timeouts[key]
if default is not sentinel:
return dict.pop(self,key,default)
else:
return dict.pop(self,key)
finally:
self._lock.release()
def __setitem__(self,key,value):
return self.set_item(key,value)
def set_item(self,key,value,timeout=None,timeout_callback=None):
"""Set item of the dictionary.
:Parameters:
- `key`: the key.
- `value`: the object to store.
- `timeout`: timeout value for the object (in seconds from now).
- `timeout_callback`: function to be called when the item expires.
The callback should accept none, one (the key) or two (the key
and the value) arguments.
:Types:
- `key`: any hashable value
- `value`: any python object
- `timeout`: `int`
- `timeout_callback`: callable"""
self._lock.acquire()
try:
if not timeout:
timeout=self._default_timeout
self._timeouts[key]=(time.time()+timeout,timeout_callback)
return dict.__setitem__(self,key,value)
finally:
self._lock.release()
def expire(self):
"""Do the expiration of dictionary items.
Remove items that expired by now from the dictionary."""
self._lock.acquire()
try:
for k in self._timeouts.keys():
self._expire_item(k)
finally:
self._lock.release()
def _expire_item(self,key):
"""Do the expiration of a dictionary item.
Remove the item if it has expired by now.
:Parameters:
- `key`: key to the object.
:Types:
- `key`: any hashable value"""
(timeout,callback)=self._timeouts[key]
if timeout<=time.time():
item = dict.pop(self, key)
del self._timeouts[key]
if callback:
try:
callback(key,item)
except TypeError:
try:
callback(key)
except TypeError:
callback()
# vi: sts=4 et sw=4
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