class CacheRegion(object):
"""A front end to a particular cache backend.
:param name: Optional, a string name for the region.
This isn't used internally
but can be accessed via the ``.name`` parameter, helpful
for configuring a region from a config file.
:param function_key_generator: Optional. A
function that will produce a "cache key" given
a data creation function and arguments, when using
the :meth:`.CacheRegion.cache_on_arguments` method.
The structure of this function
should be two levels: given the data creation function,
return a new function that generates the key based on
the given arguments. Such as::
def my_key_generator(namespace, fn, **kw):
fname = fn.__name__
def generate_key(*arg):
return namespace + "_" + fname + "_".join(str(s) for s in arg)
return generate_key
region = make_region(
function_key_generator = my_key_generator
).configure(
"yosai_dpcache.cache.dbm",
expiration_time=300,
arguments={
"filename":"file.dbm"
}
)
The ``namespace`` is that passed to
:meth:`.CacheRegion.cache_on_arguments`. It's not consulted
outside this function, so in fact can be of any form.
For example, it can be passed as a tuple, used to specify
arguments to pluck from \**kw::
def my_key_generator(namespace, fn):
def generate_key(*arg, **kw):
return ":".join(
[kw[k] for k in namespace] +
[str(x) for x in arg]
)
return generate_key
Where the decorator might be used as::
@my_region.cache_on_arguments(namespace=('x', 'y'))
def my_function(a, b, **kw):
return my_data()
:param function_multi_key_generator: Optional.
Similar to ``function_key_generator`` parameter, but it's used in
:meth:`.CacheRegion.cache_multi_on_arguments`. Generated function
should return list of keys. For example::
def my_multi_key_generator(namespace, fn, **kw):
namespace = fn.__name__ + (namespace or '')
def generate_keys(*args):
return [namespace + ':' + str(a) for a in args]
return generate_keys
:param key_mangler: Function which will be used on all incoming
keys before passing to the backend. Defaults to ``None``,
in which case the key mangling function recommended by
the cache backend will be used. A typical mangler
is the SHA1 mangler found at :func:`.sha1_mangle_key`
which coerces keys into a SHA1
hash, so that the string length is fixed. To
disable all key mangling, set to ``False``. Another typical
mangler is the built-in Python function ``str``, which can be used
to convert non-string or Unicode keys to bytestrings, which is
needed when using a backend such as bsddb or dbm under Python 2.x
in conjunction with Unicode keys.
:param async_creation_runner: A callable that, when specified,
will be passed to and called by dogpile.lock when
there is a stale value present in the cache. It will be passed the
mutex and is responsible releasing that mutex when finished.
This can be used to defer the computation of expensive creator
functions to later points in the future by way of, for example, a
background thread, a long-running queue, or a task manager system
like Celery.
For a specific example using async_creation_runner, new values can
be created in a background thread like so::
import threading
def async_creation_runner(cache, somekey, creator, mutex):
''' Used by dogpile.core:Lock when appropriate '''
def runner():
try:
value = creator()
cache.set(somekey, value)
finally:
mutex.release()
thread = threading.Thread(target=runner)
thread.start()
region = make_region(
async_creation_runner=async_creation_runner,
).configure(
'yosai_dpcache.cache.memcached',
expiration_time=5,
arguments={
'url': '127.0.0.1:11211',
'distributed_lock': True,
}
)
Remember that the first request for a key with no associated
value will always block; async_creator will not be invoked.
However, subsequent requests for cached-but-expired values will
still return promptly. They will be refreshed by whatever
asynchronous means the provided async_creation_runner callable
implements.
By default the async_creation_runner is disabled and is set
to ``None``.
.. versionadded:: 0.4.2 added the async_creation_runner
feature.
"""
def __init__(
self,
name=None,
function_key_generator=function_key_generator,
function_multi_key_generator=function_multi_key_generator,
key_mangler=None,
async_creation_runner=None,
):
"""Construct a new :class:`.CacheRegion`."""
self.name = name
self.function_key_generator = function_key_generator
self.function_multi_key_generator = function_multi_key_generator
self.key_mangler = self._user_defined_key_mangler = key_mangler
self.async_creation_runner = async_creation_runner
def configure(
self, backend,
expiration_time,
arguments=None,
_config_argument_dict=None,
_config_prefix=None,
wrap=None,
replace_existing_backend=False,
):
"""Configure a :class:`.CacheRegion`.
The :class:`.CacheRegion` itself
is returned.
:param backend: Required. This is the name of the
:class:`.CacheBackend` to use, and is resolved by loading
the class from the ``yosai_dpcache.cache`` entrypoint.
:param expiration_time: Required. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
:param wrap: Optional. A list of tuples, each that contains a
:class:`.ProxyBackend` and any arguments required for ProxyBackend
initialization, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
:param replace_existing_backend: if True, the existing cache backend
will be replaced. Without this flag, an exception is raised if
a backend is already configured.
"""
if "backend" in self.__dict__ and not replace_existing_backend:
raise exception.RegionAlreadyConfigured(
"This region is already "
"configured with backend: %s. "
"Specify replace_existing_backend=True to replace."
% self.backend)
backend_cls = _backend_loader.load(backend)
if _config_argument_dict:
self.backend = backend_cls.from_config_dict(
_config_argument_dict,
_config_prefix
)
else:
self.backend = backend_cls(arguments or {})
if not expiration_time or isinstance(expiration_time, Number):
self.expiration_time = expiration_time
elif isinstance(expiration_time, datetime.timedelta):
self.expiration_time = int(
compat.timedelta_total_seconds(expiration_time))
else:
raise exception.ValidationError(
'expiration_time is not a number or timedelta.')
if not self._user_defined_key_mangler:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
if getattr(wrap, '__iter__', False):
for wrapper in reversed(wrap):
self.wrap(wrapper)
return self
def wrap(self, proxy):
''' Takes a ProxyBackend instance or class and wraps the
attached backend.
proxy is a Tuple that looks like this:
(ProxyClass, arg1, arg2, ...)
'''
# if we were passed a type rather than an instance then
# initialize it.
if not issubclass(proxy[0], ProxyBackend):
raise TypeError("Type %s is not a valid ProxyBackend"
% type(proxy[0]))
proxy = proxy[0](*proxy[1:])
self.backend = proxy.wrap(self.backend)
def _mutex(self, key):
return self._lock_registry.get(key)
class _LockWrapper(object):
"""weakref-capable wrapper for threading.Lock"""
def __init__(self):
self.lock = threading.Lock()
def acquire(self, wait=True):
return self.lock.acquire(wait)
def release(self):
self.lock.release()
def _create_mutex(self, key):
mutex = self.backend.get_mutex(key)
if mutex is not None:
return mutex
else:
return self._LockWrapper()
def configure_from_config(self, config_dict, prefix):
"""Configure from a configuration dictionary
and a prefix.
Example::
local_region = make_region()
memcached_region = make_region()
# regions are ready to use for function
# decorators, but not yet for actual caching
# later, when config is available
myconfig = {
"cache.local.backend":"yosai_dpcache.cache.dbm",
"cache.local.arguments.filename":"/path/to/dbmfile.dbm",
"cache.memcached.backend":"yosai_dpcache.cache.pylibmc",
"cache.memcached.arguments.url":"127.0.0.1, 10.0.0.1",
}
local_region.configure_from_config(myconfig, "cache.local.")
memcached_region.configure_from_config(myconfig,
"cache.memcached.")
"""
config_dict = coerce_string_conf(config_dict)
return self.configure(
config_dict["%sbackend" % prefix],
expiration_time=config_dict.get(
"%sexpiration_time" % prefix, None),
_config_argument_dict=config_dict,
_config_prefix="%sarguments." % prefix,
wrap=config_dict.get(
"%swrap" % prefix, None),
)
@memoized_property
def backend(self):
raise exception.RegionNotConfigured(
"No backend is configured on this region.")
@property
def is_configured(self):
"""Return True if the backend has been configured via the
:meth:`.CacheRegion.configure` method already.
.. versionadded:: 0.5.1
"""
return 'backend' in self.__dict__
def get(self, key):
"""
Return a value from the cache based on the given key
If the value is not present, the method returns the token
``NO_VALUE``. ``NO_VALUE`` evaluates to False, but is separate from
``None`` to distinguish between a cached value of ``None``.
:param key: Key to be retrieved. While it's typical for a key to be a
string, it is ultimately passed directly down to the cache backend,
before being optionally processed by the key_mangler function, so can
be of any type recognized by the backend or by the key_mangler
function, if present.
"""
if self.key_mangler:
key = self.key_mangler(key)
return self.backend.get(key)
def get_or_create(self, key, creator_func, creator, expiration):
"""
Return a cached value based on the given key.
If a previous value is available, that value is returned immediately
and without blocking.
If the requested value does not exist in cache, the provided creation
function is used to re-create a value and persist it to cache.
The creation function is used when a *dogpile lock* is acquired. If the
*dogpile lock* cannot be acquired it is because another thread or process
is already running a creation function against cache for the provided key.
If no previous value is available and the dogpile lock cannot be acquired,
get_or_create will block until the lock is released and a new value is
available.
:param key: Key to retrieve. While it's typical for a key to be a
string, it is ultimately passed directly down to the cache backend,
before being optionally processed by the key_mangler function, so can
be of any type recognized by the backend or by the key_mangler
function, if present.
:param creator_func: function used to create a new value
:param creator: the instance to run creator_func
:param expiration: expiration time that will overide
the expiration time already configured on this :class:`.CacheRegion`
"""
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
value = self.backend.get(key)
if value is None:
raise NeedRegenerationException()
return value
def gen_value():
created_value = creator_func(creator)
self.backend.set(key, created_value, expiration)
return created_value
with Lock(self._mutex(key), gen_value, get_value) as value:
return value
def hmget_or_create(self, key, keys, creator_func, creator, expiration):
"""
Returns one or more cached values from a hash based on the given keys.
If a previous value is available, that value is returned immediately
and without blocking.
If the requested hash, not hash values, does not exist in cache, the provided
creation function is used to re-create and persist a hash to cache.
The creation function is used when a *dogpile lock* is acquired. If the
*dogpile lock* cannot be acquired it is because another thread or process
is already running a creation function against cache for the provided key.
If no previous value is available and the dogpile lock cannot be acquired,
get_or_create will block until the lock is released and a new value is
available.
:param key: Key to retrieve. While it's typical for a key to be a
string, it is ultimately passed directly down to the cache backend,
before being optionally processed by the key_mangler function, so can
be of any type recognized by the backend or by the key_mangler
function, if present.
:param creator_func: function used to create a new value
:param creator: the instance to run creator_func
:param expiration: expiration time that will overide
the expiration time already configured on this :class:`.CacheRegion`
"""
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
if not self.backend.exists(key):
raise NeedRegenerationException()
return self.backend.hmget(key, keys)
def gen_value():
created_value = creator_func(creator)
self.backend.hmset(key, created_value, expiration)
return self.backend.hmget(key, keys)
with Lock(self._mutex(key), gen_value, get_value) as value:
return value
def set(self, key, value, expiration=None):
"""Place a new value in the cache under the given key."""
if self.key_mangler:
key = self.key_mangler(key)
exp = expiration if expiration else self.expiration_time
self.backend.set(key, value, exp)
def delete(self, key):
"""Remove a value from the cache.
This operation is idempotent (can be called multiple times, or on a
non-existent key, safely)
"""
if self.key_mangler:
key = self.key_mangler(key)
self.backend.delete(key)
def keys(self, pattern):
"""
searches for keys matching pattern, returns accordingly
:returns: list of bytestrings
"""
return self.backend.keys(pattern)
def configure(
self, backend,
expiration_time,
arguments=None,
_config_argument_dict=None,
_config_prefix=None,
wrap=None,
replace_existing_backend=False,
):
"""Configure a :class:`.CacheRegion`.
The :class:`.CacheRegion` itself
is returned.
:param backend: Required. This is the name of the
:class:`.CacheBackend` to use, and is resolved by loading
the class from the ``yosai_dpcache.cache`` entrypoint.
:param expiration_time: Required. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
:param wrap: Optional. A list of tuples, each that contains a
:class:`.ProxyBackend` and any arguments required for ProxyBackend
initialization, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
:param replace_existing_backend: if True, the existing cache backend
will be replaced. Without this flag, an exception is raised if
a backend is already configured.
"""
if "backend" in self.__dict__ and not replace_existing_backend:
raise exception.RegionAlreadyConfigured(
"This region is already "
"configured with backend: %s. "
"Specify replace_existing_backend=True to replace."
% self.backend)
backend_cls = _backend_loader.load(backend)
if _config_argument_dict:
self.backend = backend_cls.from_config_dict(
_config_argument_dict,
_config_prefix
)
else:
self.backend = backend_cls(arguments or {})
if not expiration_time or isinstance(expiration_time, Number):
self.expiration_time = expiration_time
elif isinstance(expiration_time, datetime.timedelta):
self.expiration_time = int(
compat.timedelta_total_seconds(expiration_time))
else:
raise exception.ValidationError(
'expiration_time is not a number or timedelta.')
if not self._user_defined_key_mangler:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
if getattr(wrap, '__iter__', False):
for wrapper in reversed(wrap):
self.wrap(wrapper)
return self
