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"""
Redis Backends
------------------
Provides backends for talking to `redis <redis.io>`_.
"""
from __future__ import absolute_import
from dogpile.cache.api import CacheBackend, NO_VALUE
from dogpile.cache.util import pickle
import random
import time
class RedisBackend(CacheBackend):
"""A `Redis <http://redis.io/>`_ backend.
Example configuration::
from dogpile.cache import make_region
region = make_region().configure(
'dogpile.cache.redis',
arguments = {
'host': 'localhost',
'port': 6379,
'db': 0,
'redis_expiration_time': 60*60*2, # 2 hours
}
)
Arguments accepted in the arguments dictionary:
:param host: string, default is ``localhost``.
:param port: integer, default is ``6379``.
:param db: integer, default is ``0``.
:param redis_expiration_time: integer, number of seconds after setting
a value that Redis should expire it. This should be larger than dogpile's
cache expiration. By default no expiration is set.
"""
def __init__(self, arguments):
self._imports()
self.host = arguments.pop('host', 'localhost')
self.port = arguments.pop('port', 6379)
self.db = arguments.pop('db', 0)
self.distributed_lock = arguments.get('distributed_lock', False)
self.redis_expiration_time = arguments.pop('redis_expiration_time', 0)
self.client = self._create_client()
def _imports(self):
# defer imports until backend is used
global redis
import redis
def _create_client(self):
# creates client instace (so test harness can test connection)
return redis.StrictRedis(host=self.host, port=self.port, db=self.db)
def get_mutex(self, key):
if self.distributed_lock:
return RedisLock(lambda: self.client, key)
else:
return None
def get(self, key):
value = self.client.get(key)
if value is None:
return NO_VALUE
return pickle.loads(value)
def set(self, key, value):
if self.redis_expiration_time:
self.client.setex(key, self.redis_expiration_time,
pickle.dumps(value))
else:
self.client.set(key, pickle.dumps(value))
def delete(self, key):
self.client.delete(key)
class RedisLock(object):
def __init__(self, client_fn, key):
self.client_fn = client_fn
self.key = "_lock" + key
def acquire(self, wait=True):
client = self.client_fn()
i = 0
while True:
if client.setnx(self.key, 1):
return True
elif not wait:
return False
else:
sleep_time = (((i+1)*random.random()) + 2**i) / 2.5
time.sleep(sleep_time)
if i < 15:
i += 1
def release(self):
client = self.client_fn()
client.delete(self.key)
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