def configure(self,
backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
"""
if "backend" in self.__dict__:
raise Exception("This region is already "
"configured with backend: %s" % 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 {})
self.expiration_time = expiration_time
if self.key_mangler is None:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
return self
def configure(self, backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None
):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
"""
if "backend" in self.__dict__:
raise Exception(
"This region is already "
"configured with backend: %s"
% 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 {})
self.expiration_time = expiration_time
if self.key_mangler is None:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
return self
def _test_multi(self, num_threads,
expiretime,
creation_time,
num_usages,
usage_time,
delay_time,
cache_expire_time=None,
slow_write_time=None,
inline_create='rudimental'):
if slow_write_time:
dogpile_cls = SyncReaderDogpile
else:
dogpile_cls = Dogpile
# the registry feature should not be used
# unless the value + created time func is used.
use_registry = inline_create == 'get_value_plus_created'
if use_registry:
reg = NameRegistry(lambda key, exptime: dogpile_cls(exptime))
get_dogpile = lambda: reg.get("somekey", expiretime)
else:
dogpile = dogpile_cls(expiretime)
get_dogpile = lambda: dogpile
unsafe_cache = False
if cache_expire_time:
if cache_expire_time == 'unsafe':
unsafe_cache = True
cache_expire_time = expiretime *.8
elif cache_expire_time == 'safe':
cache_expire_time = (expiretime + creation_time) * 1.1
else:
assert False, cache_expire_time
log.info("Cache expire time: %s", cache_expire_time)
effective_expiretime = min(cache_expire_time, expiretime)
else:
effective_expiretime = expiretime
effective_creation_time= creation_time
if slow_write_time:
effective_creation_time += slow_write_time
max_stale = (effective_expiretime + effective_creation_time +
usage_time + delay_time) * 1.1
the_resource = []
slow_waiters = [0]
failures = [0]
def create_impl(dogpile):
log.debug("creating resource...")
time.sleep(creation_time)
if slow_write_time:
with dogpile.acquire_write_lock():
saved = list(the_resource)
# clear out the resource dict so that
# usage threads hitting it will
# raise
the_resource[:] = []
time.sleep(slow_write_time)
the_resource[:] = saved
the_resource.append(time.time())
return the_resource[-1]
if inline_create == 'get_value_plus_created':
def create_resource(dogpile):
with self._assert_synchronized():
value = create_impl(dogpile)
return value, time.time()
else:
def create_resource(dogpile):
with self._assert_synchronized():
return create_impl(dogpile)
if cache_expire_time:
def get_value():
if not the_resource:
raise NeedRegenerationException()
if time.time() - the_resource[-1] > cache_expire_time:
# should never hit a cache invalidation
# if we've set expiretime below the cache
# expire time (assuming a cache which
# honors this).
self._assert_log(
cache_expire_time < expiretime,
"Cache expiration hit, cache "
"expire time %s, expiretime %s",
cache_expire_time,
expiretime,
)
raise NeedRegenerationException()
if inline_create == 'get_value_plus_created':
return the_resource[-1], the_resource[-1]
else:
return the_resource[-1]
else:
def get_value():
if not the_resource:
raise NeedRegenerationException()
if inline_create == 'get_value_plus_created':
return the_resource[-1], the_resource[-1]
else:
return the_resource[-1]
if inline_create == 'rudimental':
assert not cache_expire_time
@contextlib.contextmanager
def enter_dogpile_block(dogpile):
with dogpile.acquire(lambda: create_resource(dogpile)) as x:
yield the_resource[-1]
elif inline_create == 'get_value':
@contextlib.contextmanager
def enter_dogpile_block(dogpile):
with dogpile.acquire(
lambda: create_resource(dogpile),
get_value
) as rec:
yield rec
elif inline_create == 'get_value_plus_created':
@contextlib.contextmanager
def enter_dogpile_block(dogpile):
with dogpile.acquire(
lambda: create_resource(dogpile),
value_and_created_fn=get_value
) as rec:
yield rec
else:
assert False, inline_create
def use_dogpile():
try:
for i in range(num_usages):
dogpile = get_dogpile()
now = time.time()
with enter_dogpile_block(dogpile) as value:
waited = time.time() - now
if waited > .01:
slow_waiters[0] += 1
check_value(value, waited)
time.sleep(usage_time)
time.sleep(delay_time)
except:
log.error("thread failed", exc_info=True)
failures[0] += 1
def check_value(value, waited):
assert value, repr(value)
# time since the current resource was
# created
time_since_create = time.time() - value
self._assert_log(
time_since_create < max_stale,
"Time since create %.4f max stale time %s, "
"total waited %s",
time_since_create, max_stale,
slow_waiters[0]
)
started_at = time.time()
threads = []
for i in range(num_threads):
t = threading.Thread(target=use_dogpile)
t.start()
threads.append(t)
for t in threads:
t.join()
actual_run_time = time.time() - started_at
# time spent starts with num usages * time per usage, with a 10% fudge
expected_run_time = (num_usages * (usage_time + delay_time)) * 1.1
expected_generations = math.ceil(expected_run_time / effective_expiretime)
if unsafe_cache:
expected_slow_waiters = expected_generations * num_threads
else:
expected_slow_waiters = expected_generations + num_threads - 1
if slow_write_time:
expected_slow_waiters = num_threads * expected_generations
# time spent also increments by one wait period in the beginning...
expected_run_time += effective_creation_time
# and a fudged version of the periodic waiting time anticipated
# for a single thread...
expected_run_time += (expected_slow_waiters * effective_creation_time) / num_threads
expected_run_time *= 1.1
log.info("Test Summary")
log.info("num threads: %s; expiretime: %s; creation_time: %s; "
"num_usages: %s; "
"usage_time: %s; delay_time: %s",
num_threads, expiretime, creation_time, num_usages,
usage_time, delay_time
)
log.info("cache expire time: %s; unsafe cache: %s slow "
"write time: %s; inline: %s; registry: %s",
cache_expire_time, unsafe_cache, slow_write_time,
inline_create, use_registry)
log.info("Estimated run time %.2f actual run time %.2f",
expected_run_time, actual_run_time)
log.info("Effective expiretime (min(cache_exp_time, exptime)) %s",
effective_expiretime)
log.info("Expected slow waits %s, Total slow waits %s",
expected_slow_waiters, slow_waiters[0])
log.info("Total generations %s Max generations expected %s" % (
len(the_resource), expected_generations
))
assert not failures[0], "%s failures occurred" % failures[0]
assert actual_run_time <= expected_run_time
assert slow_waiters[0] <= expected_slow_waiters, \
"Number of slow waiters %s exceeds expected slow waiters %s" % (
slow_waiters[0],
expected_slow_waiters
)
assert len(the_resource) <= expected_generations,\
"Number of resource generations %d exceeded "\
"expected %d" % (len(the_resource),
expected_generations)
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(
"dogpile.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(
'dogpile.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._hard_invalidated = None
self._soft_invalidated = None
self.async_creation_runner = async_creation_runner
def configure(
self,
backend,
expiration_time=None,
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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
.. versionadded 0.5.0
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
: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 :class:`.ProxyBackend`
classes and/or instances, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
.. versionadded:: 0.5.0
.. seealso::
:ref:`changing_backend_behavior`
: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.
.. versionadded:: 0.5.7
"""
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. '''
# if we were passed a type rather than an instance then
# initialize it.
if type(proxy) == type:
proxy = proxy()
if not issubclass(type(proxy), ProxyBackend):
raise TypeError("Type %s is not a valid ProxyBackend" %
type(proxy))
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 invalidate(self, hard=True):
"""Invalidate this :class:`.CacheRegion`.
Invalidation works by setting a current timestamp
(using ``time.time()``)
representing the "minimum creation time" for
a value. Any retrieved value whose creation
time is prior to this timestamp
is considered to be stale. It does not
affect the data in the cache in any way, and is also
local to this instance of :class:`.CacheRegion`.
Once set, the invalidation time is honored by
the :meth:`.CacheRegion.get_or_create`,
:meth:`.CacheRegion.get_or_create_multi` and
:meth:`.CacheRegion.get` methods.
The method supports both "hard" and "soft" invalidation
options. With "hard" invalidation,
:meth:`.CacheRegion.get_or_create` will force an immediate
regeneration of the value which all getters will wait for.
With "soft" invalidation, subsequent getters will return the
"old" value until the new one is available.
Usage of "soft" invalidation requires that the region or the method
is given a non-None expiration time.
.. versionadded:: 0.3.0
:param hard: if True, cache values will all require immediate
regeneration; dogpile logic won't be used. If False, the
creation time of existing values will be pushed back before
the expiration time so that a return+regen will be invoked.
.. versionadded:: 0.5.1
"""
if hard:
self._hard_invalidated = time.time()
self._soft_invalidated = None
else:
self._hard_invalidated = None
self._soft_invalidated = time.time()
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":"dogpile.cache.dbm",
"cache.local.arguments.filename":"/path/to/dbmfile.dbm",
"cache.memcached.backend":"dogpile.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, expiration_time=None, ignore_expiration=False):
"""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``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionchanged:: 0.3.0
:meth:`.CacheRegion.get` now checks the value's creation time
against the expiration time, rather than returning
the value unconditionally.
The method also interprets the cached value in terms
of the current "invalidation" time as set by
the :meth:`.invalidate` method. If a value is present,
but its creation time is older than the current
invalidation time, the ``NO_VALUE`` token is returned.
Passing the flag ``ignore_expiration=True`` bypasses
the invalidation time check.
.. versionadded:: 0.3.0
Support for the :meth:`.CacheRegion.invalidate`
method.
: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.
:param expiration_time: Optional expiration time value
which will supersede that configured on the :class:`.CacheRegion`
itself.
.. versionadded:: 0.3.0
:param ignore_expiration: if ``True``, the value is returned
from the cache if present, regardless of configured
expiration times or whether or not :meth:`.invalidate`
was called.
.. versionadded:: 0.3.0
"""
if self.key_mangler:
key = self.key_mangler(key)
value = self.backend.get(key)
value = self._unexpired_value_fn(expiration_time,
ignore_expiration)(value)
return value.payload
def _unexpired_value_fn(self, expiration_time, ignore_expiration):
if ignore_expiration:
return lambda value: value
else:
if expiration_time is None:
expiration_time = self.expiration_time
current_time = time.time()
invalidated = self._hard_invalidated or self._soft_invalidated
def value_fn(value):
if value is NO_VALUE:
return value
elif expiration_time is not None and \
current_time - value.metadata["ct"] > expiration_time:
return NO_VALUE
elif invalidated and \
value.metadata["ct"] < invalidated:
return NO_VALUE
else:
return value
return value_fn
def get_multi(self, keys, expiration_time=None, ignore_expiration=False):
"""Return multiple values from the cache, based on the given keys.
Returns values as a list matching the keys given.
E.g.::
values = region.get_multi(["one", "two", "three"])
To convert values to a dictionary, use ``zip()``::
keys = ["one", "two", "three"]
values = region.get_multi(keys)
dictionary = dict(zip(keys, values))
Keys which aren't present in the list are returned as
the ``NO_VALUE`` token. ``NO_VALUE`` evaluates to False,
but is separate from
``None`` to distinguish between a cached value of ``None``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionadded:: 0.5.0
"""
if not keys:
return []
if self.key_mangler:
keys = list(map(lambda key: self.key_mangler(key), keys))
backend_values = self.backend.get_multi(keys)
_unexpired_value_fn = self._unexpired_value_fn(expiration_time,
ignore_expiration)
return [
value.payload if value is not NO_VALUE else value
for value in (_unexpired_value_fn(value)
for value in backend_values)
]
def get_or_create(self,
key,
creator,
expiration_time=None,
should_cache_fn=None):
"""Return a cached value based on the given key.
If the value does not exist or is considered to be expired
based on its creation time, the given
creation function may or may not be used to recreate the value
and persist the newly generated value in the cache.
Whether or not the function is used depends on if the
*dogpile lock* can be acquired or not. If it can't, it means
a different thread or process is already running a creation
function for this key against the cache. When the dogpile
lock cannot be acquired, the method will block if no
previous value is available, until the lock is released and
a new value available. If a previous value
is available, that value is returned immediately without blocking.
If the :meth:`.invalidate` method has been called, and
the retrieved value's timestamp is older than the invalidation
timestamp, the value is unconditionally prevented from
being returned. The method will attempt to acquire the dogpile
lock to generate a new value, or will wait
until the lock is released to return the new value.
.. versionchanged:: 0.3.0
The value is unconditionally regenerated if the creation
time is older than the last call to :meth:`.invalidate`.
: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.
:param creator: function which creates a new value.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
:param should_cache_fn: optional callable function which will receive
the value returned by the "creator", and will then return True or
False, indicating if the value should actually be cached or not. If
it returns False, the value is still returned, but isn't cached.
E.g.::
def dont_cache_none(value):
return value is not None
value = region.get_or_create("some key",
create_value,
should_cache_fn=dont_cache_none)
Above, the function returns the value of create_value() if
the cache is invalid, however if the return value is None,
it won't be cached.
.. versionadded:: 0.4.3
.. seealso::
:meth:`.CacheRegion.cache_on_arguments` - applies
:meth:`.get_or_create` to any function using a decorator.
:meth:`.CacheRegion.get_or_create_multi` - multiple key/value
version
"""
orig_key = key
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
value = self.backend.get(key)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(
self._hard_invalidated and
value.metadata["ct"] < self._hard_invalidated):
raise NeedRegenerationException()
ct = value.metadata["ct"]
if self._soft_invalidated:
if ct < self._soft_invalidated:
ct = time.time() - expiration_time - .0001
return value.payload, ct
def gen_value():
created_value = creator()
value = self._value(created_value)
if not should_cache_fn or \
should_cache_fn(created_value):
self.backend.set(key, value)
return value.payload, value.metadata["ct"]
if expiration_time is None:
expiration_time = self.expiration_time
if expiration_time is None and self._soft_invalidated:
raise exception.DogpileCacheException(
"Non-None expiration time required "
"for soft invalidation")
if expiration_time == -1:
expiration_time = None
if self.async_creation_runner:
def async_creator(mutex):
return self.async_creation_runner(self, orig_key, creator,
mutex)
else:
async_creator = None
with Lock(self._mutex(key), gen_value, get_value, expiration_time,
async_creator) as value:
return value
def get_or_create_multi(self,
keys,
creator,
expiration_time=None,
should_cache_fn=None):
"""Return a sequence of cached values based on a sequence of keys.
The behavior for generation of values based on keys corresponds
to that of :meth:`.Region.get_or_create`, with the exception that
the ``creator()`` function may be asked to generate any subset of
the given keys. The list of keys to be generated is passed to
``creator()``, and ``creator()`` should return the generated values
as a sequence corresponding to the order of the keys.
The method uses the same approach as :meth:`.Region.get_multi`
and :meth:`.Region.set_multi` to get and set values from the
backend.
If you are using a :class:`.CacheBackend` or :class:`.ProxyBackend`
that modifies values, take note this function invokes
``.set_multi()`` for newly generated values using the same values it
returns to the calling function. A correct implementation of
``.set_multi()`` will not modify values in-place on the submitted
``mapping`` dict.
:param keys: Sequence of keys to be retrieved.
:param creator: function which accepts a sequence of keys and
returns a sequence of new values.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
:param should_cache_fn: optional callable function which will receive
each value returned by the "creator", and will then return True or
False, indicating if the value should actually be cached or not. If
it returns False, the value is still returned, but isn't cached.
.. versionadded:: 0.5.0
.. seealso::
:meth:`.CacheRegion.cache_multi_on_arguments`
:meth:`.CacheRegion.get_or_create`
"""
def get_value(key):
value = values.get(key, NO_VALUE)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(self._hard_invalidated and
value.metadata["ct"] < self._hard_invalidated):
# dogpile.core understands a 0 here as
# "the value is not available", e.g.
# _has_value() will return False.
return value.payload, 0
else:
ct = value.metadata["ct"]
if self._soft_invalidated:
if ct < self._soft_invalidated:
ct = time.time() - expiration_time - .0001
return value.payload, ct
def gen_value():
raise NotImplementedError()
def async_creator(key, mutex):
mutexes[key] = mutex
if expiration_time is None:
expiration_time = self.expiration_time
if expiration_time is None and self._soft_invalidated:
raise exception.DogpileCacheException(
"Non-None expiration time required "
"for soft invalidation")
if expiration_time == -1:
expiration_time = None
mutexes = {}
sorted_unique_keys = sorted(set(keys))
if self.key_mangler:
mangled_keys = [self.key_mangler(k) for k in sorted_unique_keys]
else:
mangled_keys = sorted_unique_keys
orig_to_mangled = dict(zip(sorted_unique_keys, mangled_keys))
values = dict(zip(mangled_keys, self.backend.get_multi(mangled_keys)))
for orig_key, mangled_key in orig_to_mangled.items():
with Lock(self._mutex(mangled_key),
gen_value,
lambda: get_value(mangled_key),
expiration_time,
async_creator=lambda mutex: async_creator(
orig_key, mutex)):
pass
try:
if mutexes:
# sort the keys, the idea is to prevent deadlocks.
# though haven't been able to simulate one anyway.
keys_to_get = sorted(mutexes)
new_values = creator(*keys_to_get)
values_w_created = dict(
(orig_to_mangled[k], self._value(v))
for k, v in zip(keys_to_get, new_values))
if not should_cache_fn:
self.backend.set_multi(values_w_created)
else:
self.backend.set_multi(
dict((k, v) for k, v in values_w_created.items()
if should_cache_fn(v[0])))
values.update(values_w_created)
return [values[orig_to_mangled[k]].payload for k in keys]
finally:
for mutex in mutexes.values():
mutex.release()
def _value(self, value):
"""Return a :class:`.CachedValue` given a value."""
return CachedValue(value, {"ct": time.time(), "v": value_version})
def set(self, key, value):
"""Place a new value in the cache under the given key."""
if self.key_mangler:
key = self.key_mangler(key)
self.backend.set(key, self._value(value))
def set_multi(self, mapping):
"""Place new values in the cache under the given keys.
.. versionadded:: 0.5.0
"""
if not mapping:
return
if self.key_mangler:
mapping = dict((self.key_mangler(k), self._value(v))
for k, v in mapping.items())
else:
mapping = dict((k, self._value(v)) for k, v in mapping.items())
self.backend.set_multi(mapping)
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 delete_multi(self, keys):
"""Remove multiple values from the cache.
This operation is idempotent (can be called multiple times, or on a
non-existent key, safely)
.. versionadded:: 0.5.0
"""
if self.key_mangler:
keys = list(map(lambda key: self.key_mangler(key), keys))
self.backend.delete_multi(keys)
def cache_on_arguments(self,
namespace=None,
expiration_time=None,
should_cache_fn=None,
to_str=compat.string_type,
function_key_generator=None):
"""A function decorator that will cache the return
value of the function using a key derived from the
function itself and its arguments.
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
E.g.::
@someregion.cache_on_arguments()
def generate_something(x, y):
return somedatabase.query(x, y)
The decorated function can then be called normally, where
data will be pulled from the cache region unless a new
value is needed::
result = generate_something(5, 6)
The function is also given an attribute ``invalidate()``, which
provides for invalidation of the value. Pass to ``invalidate()``
the same arguments you'd pass to the function itself to represent
a particular value::
generate_something.invalidate(5, 6)
Another attribute ``set()`` is added to provide extra caching
possibilities relative to the function. This is a convenience
method for :meth:`.CacheRegion.set` which will store a given
value directly without calling the decorated function.
The value to be cached is passed as the first argument, and the
arguments which would normally be passed to the function
should follow::
generate_something.set(3, 5, 6)
The above example is equivalent to calling
``generate_something(5, 6)``, if the function were to produce
the value ``3`` as the value to be cached.
.. versionadded:: 0.4.1 Added ``set()`` method to decorated function.
Similar to ``set()`` is ``refresh()``. This attribute will
invoke the decorated function and populate a new value into
the cache with the new value, as well as returning that value::
newvalue = generate_something.refresh(5, 6)
.. versionadded:: 0.5.0 Added ``refresh()`` method to decorated
function.
Lastly, the ``get()`` method returns either the value cached
for the given key, or the token ``NO_VALUE`` if no such key
exists::
value = generate_something.get(5, 6)
.. versionadded:: 0.5.3 Added ``get()`` method to decorated
function.
The default key generation will use the name
of the function, the module name for the function,
the arguments passed, as well as an optional "namespace"
parameter in order to generate a cache key.
Given a function ``one`` inside the module
``myapp.tools``::
@region.cache_on_arguments(namespace="foo")
def one(a, b):
return a + b
Above, calling ``one(3, 4)`` will produce a
cache key as follows::
myapp.tools:one|foo|3 4
The key generator will ignore an initial argument
of ``self`` or ``cls``, making the decorator suitable
(with caveats) for use with instance or class methods.
Given the example::
class MyClass(object):
@region.cache_on_arguments(namespace="foo")
def one(self, a, b):
return a + b
The cache key above for ``MyClass().one(3, 4)`` will
again produce the same cache key of ``myapp.tools:one|foo|3 4`` -
the name ``self`` is skipped.
The ``namespace`` parameter is optional, and is used
normally to disambiguate two functions of the same
name within the same module, as can occur when decorating
instance or class methods as below::
class MyClass(object):
@region.cache_on_arguments(namespace='MC')
def somemethod(self, x, y):
""
class MyOtherClass(object):
@region.cache_on_arguments(namespace='MOC')
def somemethod(self, x, y):
""
Above, the ``namespace`` parameter disambiguates
between ``somemethod`` on ``MyClass`` and ``MyOtherClass``.
Python class declaration mechanics otherwise prevent
the decorator from having awareness of the ``MyClass``
and ``MyOtherClass`` names, as the function is received
by the decorator before it becomes an instance method.
The function key generation can be entirely replaced
on a per-region basis using the ``function_key_generator``
argument present on :func:`.make_region` and
:class:`.CacheRegion`. If defaults to
:func:`.function_key_generator`.
:param namespace: optional string argument which will be
established as part of the cache key. This may be needed
to disambiguate functions of the same name within the same
source file, such as those
associated with classes - note that the decorator itself
can't see the parent class on a function as the class is
being declared.
:param expiration_time: if not None, will override the normal
expiration time.
May be specified as a callable, taking no arguments, that
returns a value to be used as the ``expiration_time``. This callable
will be called whenever the decorated function itself is called, in
caching or retrieving. Thus, this can be used to
determine a *dynamic* expiration time for the cached function
result. Example use cases include "cache the result until the
end of the day, week or time period" and "cache until a certain date
or time passes".
.. versionchanged:: 0.5.0
``expiration_time`` may be passed as a callable to
:meth:`.CacheRegion.cache_on_arguments`.
:param should_cache_fn: passed to :meth:`.CacheRegion.get_or_create`.
.. versionadded:: 0.4.3
:param to_str: callable, will be called on each function argument
in order to convert to a string. Defaults to ``str()``. If the
function accepts non-ascii unicode arguments on Python 2.x, the
``unicode()`` builtin can be substituted, but note this will
produce unicode cache keys which may require key mangling before
reaching the cache.
.. versionadded:: 0.5.0
:param function_key_generator: a function that will produce a
"cache key". This function will supersede the one configured on the
:class:`.CacheRegion` itself.
.. versionadded:: 0.5.5
.. seealso::
:meth:`.CacheRegion.cache_multi_on_arguments`
:meth:`.CacheRegion.get_or_create`
"""
expiration_time_is_callable = compat.callable(expiration_time)
if function_key_generator is None:
function_key_generator = self.function_key_generator
def decorator(fn):
if to_str is compat.string_type:
# backwards compatible
key_generator = function_key_generator(namespace, fn)
else:
key_generator = function_key_generator(namespace,
fn,
to_str=to_str)
@wraps(fn)
def decorate(*arg, **kw):
key = key_generator(*arg, **kw)
@wraps(fn)
def creator():
return fn(*arg, **kw)
timeout = expiration_time() if expiration_time_is_callable \
else expiration_time
return self.get_or_create(key, creator, timeout,
should_cache_fn)
def invalidate(*arg, **kw):
key = key_generator(*arg, **kw)
self.delete(key)
def set_(value, *arg, **kw):
key = key_generator(*arg, **kw)
self.set(key, value)
def get(*arg, **kw):
key = key_generator(*arg, **kw)
return self.get(key)
def refresh(*arg, **kw):
key = key_generator(*arg, **kw)
value = fn(*arg, **kw)
self.set(key, value)
return value
decorate.set = set_
decorate.invalidate = invalidate
decorate.refresh = refresh
decorate.get = get
return decorate
return decorator
def cache_multi_on_arguments(self,
namespace=None,
expiration_time=None,
should_cache_fn=None,
asdict=False,
to_str=compat.string_type,
function_multi_key_generator=None):
"""A function decorator that will cache multiple return
values from the function using a sequence of keys derived from the
function itself and the arguments passed to it.
This method is the "multiple key" analogue to the
:meth:`.CacheRegion.cache_on_arguments` method.
Example::
@someregion.cache_multi_on_arguments()
def generate_something(*keys):
return [
somedatabase.query(key)
for key in keys
]
The decorated function can be called normally. The decorator
will produce a list of cache keys using a mechanism similar to
that of :meth:`.CacheRegion.cache_on_arguments`, combining the
name of the function with the optional namespace and with the
string form of each key. It will then consult the cache using
the same mechanism as that of :meth:`.CacheRegion.get_multi`
to retrieve all current values; the originally passed keys
corresponding to those values which aren't generated or need
regeneration will be assembled into a new argument list, and
the decorated function is then called with that subset of
arguments.
The returned result is a list::
result = generate_something("key1", "key2", "key3")
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create_multi` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
Unlike the :meth:`.CacheRegion.cache_on_arguments` method,
:meth:`.CacheRegion.cache_multi_on_arguments` works only with
a single function signature, one which takes a simple list of
keys as arguments.
Like :meth:`.CacheRegion.cache_on_arguments`, the decorated function
is also provided with a ``set()`` method, which here accepts a
mapping of keys and values to set in the cache::
generate_something.set({"k1": "value1",
"k2": "value2", "k3": "value3"})
...an ``invalidate()`` method, which has the effect of deleting
the given sequence of keys using the same mechanism as that of
:meth:`.CacheRegion.delete_multi`::
generate_something.invalidate("k1", "k2", "k3")
...a ``refresh()`` method, which will call the creation
function, cache the new values, and return them::
values = generate_something.refresh("k1", "k2", "k3")
...and a ``get()`` method, which will return values
based on the given arguments::
values = generate_something.get("k1", "k2", "k3")
.. versionadded:: 0.5.3 Added ``get()`` method to decorated
function.
Parameters passed to :meth:`.CacheRegion.cache_multi_on_arguments`
have the same meaning as those passed to
:meth:`.CacheRegion.cache_on_arguments`.
:param namespace: optional string argument which will be
established as part of each cache key.
:param expiration_time: if not None, will override the normal
expiration time. May be passed as an integer or a
callable.
:param should_cache_fn: passed to
:meth:`.CacheRegion.get_or_create_multi`. This function is given a
value as returned by the creator, and only if it returns True will
that value be placed in the cache.
:param asdict: if ``True``, the decorated function should return
its result as a dictionary of keys->values, and the final result
of calling the decorated function will also be a dictionary.
If left at its default value of ``False``, the decorated function
should return its result as a list of values, and the final
result of calling the decorated function will also be a list.
When ``asdict==True`` if the dictionary returned by the decorated
function is missing keys, those keys will not be cached.
:param to_str: callable, will be called on each function argument
in order to convert to a string. Defaults to ``str()``. If the
function accepts non-ascii unicode arguments on Python 2.x, the
``unicode()`` builtin can be substituted, but note this will
produce unicode cache keys which may require key mangling before
reaching the cache.
.. versionadded:: 0.5.0
:param function_multi_key_generator: a function that will produce a
list of keys. This function will supersede the one configured on the
:class:`.CacheRegion` itself.
.. versionadded:: 0.5.5
.. seealso::
:meth:`.CacheRegion.cache_on_arguments`
:meth:`.CacheRegion.get_or_create_multi`
"""
expiration_time_is_callable = compat.callable(expiration_time)
if function_multi_key_generator is None:
function_multi_key_generator = self.function_multi_key_generator
def decorator(fn):
key_generator = function_multi_key_generator(namespace,
fn,
to_str=to_str)
@wraps(fn)
def decorate(*arg, **kw):
cache_keys = arg
keys = key_generator(*arg, **kw)
key_lookup = dict(zip(keys, cache_keys))
@wraps(fn)
def creator(*keys_to_create):
return fn(*[key_lookup[k] for k in keys_to_create])
timeout = expiration_time() if expiration_time_is_callable \
else expiration_time
if asdict:
def dict_create(*keys):
d_values = creator(*keys)
return [
d_values.get(key_lookup[k], NO_VALUE) for k in keys
]
def wrap_cache_fn(value):
if value is NO_VALUE:
return False
elif not should_cache_fn:
return True
else:
return should_cache_fn(value)
result = self.get_or_create_multi(keys, dict_create,
timeout, wrap_cache_fn)
result = dict((k, v) for k, v in zip(cache_keys, result)
if v is not NO_VALUE)
else:
result = self.get_or_create_multi(keys, creator, timeout,
should_cache_fn)
return result
def invalidate(*arg):
keys = key_generator(*arg)
self.delete_multi(keys)
def set_(mapping):
keys = list(mapping)
gen_keys = key_generator(*keys)
self.set_multi(
dict((gen_key, mapping[key])
for gen_key, key in zip(gen_keys, keys)))
def get(*arg):
keys = key_generator(*arg)
return self.get_multi(keys)
def refresh(*arg):
keys = key_generator(*arg)
values = fn(*arg)
if asdict:
self.set_multi(dict(zip(keys, [values[a] for a in arg])))
return values
else:
self.set_multi(dict(zip(keys, values)))
return values
decorate.set = set_
decorate.invalidate = invalidate
decorate.refresh = refresh
decorate.get = get
return decorate
return decorator
def configure(
self,
backend,
expiration_time=None,
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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
.. versionadded 0.5.0
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
: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 :class:`.ProxyBackend`
classes and/or instances, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
.. versionadded:: 0.5.0
.. seealso::
:ref:`changing_backend_behavior`
: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.
.. versionadded:: 0.5.7
"""
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
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):
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(
"dogpile.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]
)
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 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``.
"""
def __init__(self,
name=None,
function_key_generator=function_key_generator,
key_mangler=None
):
"""Construct a new :class:`.CacheRegion`."""
self.function_key_generator = function_key_generator
if key_mangler:
self.key_mangler = key_mangler
else:
self.key_mangler = None
self._invalidated = None
def configure(self, backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None
):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
"""
if "backend" in self.__dict__:
raise Exception(
"This region is already "
"configured with backend: %s"
% 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 {})
self.expiration_time = expiration_time
if self.key_mangler is None:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
return self
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 invalidate(self):
"""Invalidate this :class:`.CacheRegion`.
Invalidation works by setting a current timestamp
(using ``time.time()``)
representing the "minimum creation time" for
a value. Any retrieved value whose creation
time is prior to this timestamp
is considered to be stale. It does not
affect the data in the cache in any way, and is also
local to this instance of :class:`.CacheRegion`.
Once set, the invalidation time is honored by
the :meth:`.CacheRegion.get_or_create` and
:meth:`.CacheRegion.get` methods.
.. versionadded:: 0.3.0
"""
self._invalidated = time.time()
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":"dogpile.cache.dbm",
"cache.local.arguments.filename":"/path/to/dbmfile.dbm",
"cache.memcached.backend":"dogpile.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
)
@memoized_property
def backend(self):
raise Exception("No backend is configured on this region.")
def get(self, key, expiration_time=None, ignore_expiration=False):
"""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``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionchanged:: 0.3.0
:meth:`.CacheRegion.get` now checks the value's creation time
against the expiration time, rather than returning
the value unconditionally.
The method also interprets the cached value in terms
of the current "invalidation" time as set by
the :meth:`.invalidate` method. If a value is present,
but its creation time is older than the current
invalidation time, the ``NO_VALUE`` token is returned.
Passing the flag ``ignore_expiration=True`` bypasses
the invalidation time check.
.. versionadded:: 0.3.0
Support for the :meth:`.CacheRegion.invalidate`
method.
: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.
:param expiration_time: Optional expiration time value
which will supersede that configured on the :class:`.CacheRegion`
itself.
.. versionadded:: 0.3.0
:param ignore_expiration: if ``True``, the value is returned
from the cache if present, regardless of configured
expiration times or whether or not :meth:`.invalidate`
was called.
.. versionadded:: 0.3.0
"""
if self.key_mangler:
key = self.key_mangler(key)
value = self.backend.get(key)
if value is NO_VALUE:
return value
elif not ignore_expiration:
if expiration_time is None:
expiration_time = self.expiration_time
if expiration_time is not None and \
time.time() - value.metadata["ct"] > expiration_time:
return NO_VALUE
elif self._invalidated and value.metadata["ct"] < self._invalidated:
return NO_VALUE
return value.payload
def get_or_create(self, key, creator, expiration_time=None):
"""Return a cached value based on the given key.
If the value does not exist or is considered to be expired
based on its creation time, the given
creation function may or may not be used to recreate the value
and persist the newly generated value in the cache.
Whether or not the function is used depends on if the
*dogpile lock* can be acquired or not. If it can't, it means
a different thread or process is already running a creation
function for this key against the cache. When the dogpile
lock cannot be acquired, the method will block if no
previous value is available, until the lock is released and
a new value available. If a previous value
is available, that value is returned immediately without blocking.
If the :meth:`.invalidate` method has been called, and
the retrieved value's timestamp is older than the invalidation
timestamp, the value is unconditionally prevented from
being returned. The method will attempt to acquire the dogpile
lock to generate a new value, or will wait
until the lock is released to return the new value.
.. versionchanged:: 0.3.0
The value is unconditionally regenerated if the creation
time is older than the last call to :meth:`.invalidate`.
: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.
:param creator: function which creates a new value.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
See also:
:meth:`.CacheRegion.cache_on_arguments` - applies :meth:`.get_or_create`
to any function using a decorator.
"""
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
value = self.backend.get(key)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(self._invalidated and
value.metadata["ct"] < self._invalidated):
raise NeedRegenerationException()
return value.payload, value.metadata["ct"]
def gen_value():
value = self._value(creator())
self.backend.set(key, value)
return value.payload, value.metadata["ct"]
if expiration_time is None:
expiration_time = self.expiration_time
with Lock(
self._mutex(key),
gen_value,
get_value,
expiration_time) as value:
return value
def _value(self, value):
"""Return a :class:`.CachedValue` given a value."""
return CachedValue(value, {
"ct": time.time(),
"v": value_version
})
def set(self, key, value):
"""Place a new value in the cache under the given key."""
if self.key_mangler:
key = self.key_mangler(key)
self.backend.set(key, self._value(value))
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 cache_on_arguments(self, namespace=None, expiration_time=None):
"""A function decorator that will cache the return
value of the function using a key derived from the
function itself and its arguments.
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
E.g.::
@someregion.cache_on_arguments()
def generate_something(x, y):
return somedatabase.query(x, y)
The decorated function can then be called normally, where
data will be pulled from the cache region unless a new
value is needed::
result = generate_something(5, 6)
The function is also given an attribute ``invalidate``, which
provides for invalidation of the value. Pass to ``invalidate()``
the same arguments you'd pass to the function itself to represent
a particular value::
generate_something.invalidate(5, 6)
Another attribute ``set`` is added to provide extra caching
possibilities relative to the function. This is a convenience
method for :meth:`.CacheRegion.set` which will store a given
value directly without calling the decorated function.
The value to be cached is passed as the first argument, and the
arguments which would normally be passed to the function
should follow::
generate_something.set(3, 5, 6)
The above example is equivalent to calling ``generate_something(5, 6)``,
if the function were to produce the value ``3`` as the value to be
cached.
.. versionadded:: 0.4.1 Added set() method to decorated function.
The default key generation will use the name
of the function, the module name for the function,
the arguments passed, as well as an optional "namespace"
parameter in order to generate a cache key.
Given a function ``one`` inside the module
``myapp.tools``::
@region.cache_on_arguments(namespace="foo")
def one(a, b):
return a + b
Above, calling ``one(3, 4)`` will produce a
cache key as follows::
myapp.tools:one|foo|3 4
The key generator will ignore an initial argument
of ``self`` or ``cls``, making the decorator suitable
(with caveats) for use with instance or class methods.
Given the example::
class MyClass(object):
@region.cache_on_arguments(namespace="foo")
def one(self, a, b):
return a + b
The cache key above for ``MyClass().one(3, 4)`` will
again produce the same cache key of ``myapp.tools:one|foo|3 4`` -
the name ``self`` is skipped.
The ``namespace`` parameter is optional, and is used
normally to disambiguate two functions of the same
name within the same module, as can occur when decorating
instance or class methods as below::
class MyClass(object):
@region.cache_on_arguments(namespace='MC')
def somemethod(self, x, y):
""
class MyOtherClass(object):
@region.cache_on_arguments(namespace='MOC')
def somemethod(self, x, y):
""
Above, the ``namespace`` parameter disambiguates
between ``somemethod`` on ``MyClass`` and ``MyOtherClass``.
Python class declaration mechanics otherwise prevent
the decorator from having awareness of the ``MyClass``
and ``MyOtherClass`` names, as the function is received
by the decorator before it becomes an instance method.
The function key generation can be entirely replaced
on a per-region basis using the ``function_key_generator``
argument present on :func:`.make_region` and
:class:`.CacheRegion`. If defaults to
:func:`.function_key_generator`.
:param namespace: optional string argument which will be
established as part of the cache key. This may be needed
to disambiguate functions of the same name within the same
source file, such as those
associated with classes - note that the decorator itself
can't see the parent class on a function as the class is
being declared.
:param expiration_time: if not None, will override the normal
expiration time.
"""
def decorator(fn):
key_generator = self.function_key_generator(namespace, fn)
@wraps(fn)
def decorate(*arg, **kw):
key = key_generator(*arg, **kw)
def creator():
return fn(*arg, **kw)
return self.get_or_create(key, creator, expiration_time)
def invalidate(*arg, **kw):
key = key_generator(*arg, **kw)
self.delete(key)
def set_(value, *arg, **kw):
key = key_generator(*arg, **kw)
self.set(key, value)
decorate.set = set_
decorate.invalidate = invalidate
return decorate
return decorator
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(
"dogpile.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(
'dogpile.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
if key_mangler:
self.key_mangler = key_mangler
else:
self.key_mangler = None
self._invalidated = None
self.async_creation_runner = async_creation_runner
def configure(self, backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None,
wrap=None
):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
.. versionadded 0.5.0
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
: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 :class:`.ProxyBackend`
classes and/or instances, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
.. versionadded:: 0.5.0
.. seealso::
:ref:`changing_backend_behavior`
"""
if "backend" in self.__dict__:
raise Exception(
"This region is already "
"configured with backend: %s"
% 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(expiration_time.total_seconds())
else:
raise Exception('expiration_time is not a number or timedelta.')
if self.key_mangler is None:
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. '''
# if we were passed a type rather than an instance then
# initialize it.
if type(proxy) == type:
proxy = proxy()
if not issubclass(type(proxy), ProxyBackend):
raise Exception("Type %s is not a valid ProxyBackend"
% type(proxy))
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 invalidate(self):
"""Invalidate this :class:`.CacheRegion`.
Invalidation works by setting a current timestamp
(using ``time.time()``)
representing the "minimum creation time" for
a value. Any retrieved value whose creation
time is prior to this timestamp
is considered to be stale. It does not
affect the data in the cache in any way, and is also
local to this instance of :class:`.CacheRegion`.
Once set, the invalidation time is honored by
the :meth:`.CacheRegion.get_or_create` and
:meth:`.CacheRegion.get` methods.
.. versionadded:: 0.3.0
"""
self._invalidated = time.time()
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":"dogpile.cache.dbm",
"cache.local.arguments.filename":"/path/to/dbmfile.dbm",
"cache.memcached.backend":"dogpile.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
)
@memoized_property
def backend(self):
raise Exception("No backend is configured on this region.")
def get(self, key, expiration_time=None, ignore_expiration=False):
"""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``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionchanged:: 0.3.0
:meth:`.CacheRegion.get` now checks the value's creation time
against the expiration time, rather than returning
the value unconditionally.
The method also interprets the cached value in terms
of the current "invalidation" time as set by
the :meth:`.invalidate` method. If a value is present,
but its creation time is older than the current
invalidation time, the ``NO_VALUE`` token is returned.
Passing the flag ``ignore_expiration=True`` bypasses
the invalidation time check.
.. versionadded:: 0.3.0
Support for the :meth:`.CacheRegion.invalidate`
method.
: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.
:param expiration_time: Optional expiration time value
which will supersede that configured on the :class:`.CacheRegion`
itself.
.. versionadded:: 0.3.0
:param ignore_expiration: if ``True``, the value is returned
from the cache if present, regardless of configured
expiration times or whether or not :meth:`.invalidate`
was called.
.. versionadded:: 0.3.0
"""
if self.key_mangler:
key = self.key_mangler(key)
value = self.backend.get(key)
value = self._unexpired_value_fn(
expiration_time, ignore_expiration)(value)
return value.payload
def _unexpired_value_fn(self, expiration_time, ignore_expiration):
if ignore_expiration:
return lambda value: value
else:
if expiration_time is None:
expiration_time = self.expiration_time
current_time = time.time()
def value_fn(value):
if value is NO_VALUE:
return value
elif expiration_time is not None and \
current_time - value.metadata["ct"] > expiration_time:
return NO_VALUE
elif self._invalidated and \
value.metadata["ct"] < self._invalidated:
return NO_VALUE
else:
return value
return value_fn
def get_multi(self, keys, expiration_time=None, ignore_expiration=False):
"""Return multiple values from the cache, based on the given keys.
Returns values as a list matching the keys given.
E.g.::
values = region.get_multi(["one", "two", "three"])
To convert values to a dictionary, use ``zip()``::
keys = ["one", "two", "three"]
values = region.get_multi(keys)
dictionary = dict(zip(keys, values))
Keys which aren't present in the list are returned as
the ``NO_VALUE`` token. ``NO_VALUE`` evaluates to False,
but is separate from
``None`` to distinguish between a cached value of ``None``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionadded:: 0.5.0
"""
if self.key_mangler:
keys = map(lambda key: self.key_mangler(key), keys)
backend_values = self.backend.get_multi(keys)
_unexpired_value_fn = self._unexpired_value_fn(
expiration_time, ignore_expiration)
return [
value.payload if value is not NO_VALUE else value
for value in
(
_unexpired_value_fn(value) for value in
backend_values
)
]
def get_or_create(self, key, creator, expiration_time=None,
should_cache_fn=None):
"""Return a cached value based on the given key.
If the value does not exist or is considered to be expired
based on its creation time, the given
creation function may or may not be used to recreate the value
and persist the newly generated value in the cache.
Whether or not the function is used depends on if the
*dogpile lock* can be acquired or not. If it can't, it means
a different thread or process is already running a creation
function for this key against the cache. When the dogpile
lock cannot be acquired, the method will block if no
previous value is available, until the lock is released and
a new value available. If a previous value
is available, that value is returned immediately without blocking.
If the :meth:`.invalidate` method has been called, and
the retrieved value's timestamp is older than the invalidation
timestamp, the value is unconditionally prevented from
being returned. The method will attempt to acquire the dogpile
lock to generate a new value, or will wait
until the lock is released to return the new value.
.. versionchanged:: 0.3.0
The value is unconditionally regenerated if the creation
time is older than the last call to :meth:`.invalidate`.
: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.
:param creator: function which creates a new value.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
:param should_cache_fn: optional callable function which will receive the
value returned by the "creator", and will then return True or False,
indicating if the value should actually be cached or not. If it
returns False, the value is still returned, but isn't cached.
E.g.::
def dont_cache_none(value):
return value is not None
value = region.get_or_create("some key",
create_value,
should_cache_fn=dont_cache_none)
Above, the function returns the value of create_value() if
the cache is invalid, however if the return value is None,
it won't be cached.
.. versionadded:: 0.4.3
.. seealso::
:meth:`.CacheRegion.cache_on_arguments` - applies
:meth:`.get_or_create` to any function using a decorator.
:meth:`.CacheRegion.get_or_create_multi` - multiple key/value version
"""
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
value = self.backend.get(key)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(self._invalidated and
value.metadata["ct"] < self._invalidated):
raise NeedRegenerationException()
return value.payload, value.metadata["ct"]
def gen_value():
created_value = creator()
value = self._value(created_value)
if not should_cache_fn or \
should_cache_fn(created_value):
self.backend.set(key, value)
return value.payload, value.metadata["ct"]
if expiration_time is None:
expiration_time = self.expiration_time
if self.async_creation_runner:
def async_creator(mutex):
return self.async_creation_runner(self, key, creator, mutex)
else:
async_creator = None
with Lock(
self._mutex(key),
gen_value,
get_value,
expiration_time,
async_creator) as value:
return value
def get_or_create_multi(self, keys, creator, expiration_time=None,
should_cache_fn=None):
"""Return a sequence of cached values based on a sequence of keys.
The behavior for generation of values based on keys corresponds
to that of :meth:`.Region.get_or_create`, with the exception that
the ``creator()`` function may be asked to generate any subset of
the given keys. The list of keys to be generated is passed to
``creator()``, and ``creator()`` should return the generated values
as a sequence corresponding to the order of the keys.
The method uses the same approach as :meth:`.Region.get_multi`
and :meth:`.Region.set_multi` to get and set values from the
backend.
:param keys: Sequence of keys to be retrieved.
:param creator: function which accepts a sequence of keys and
returns a sequence of new values.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
:param should_cache_fn: optional callable function which will receive
each value returned by the "creator", and will then return True or False,
indicating if the value should actually be cached or not. If it
returns False, the value is still returned, but isn't cached.
.. versionadded:: 0.5.0
.. seealso::
:meth:`.CacheRegion.cache_multi_on_arguments`
:meth:`.CacheRegion.get_or_create`
"""
def get_value(key):
value = values.get(key, NO_VALUE)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(self._invalidated and
value.metadata["ct"] < self._invalidated):
return value.payload, 0
else:
return value.payload, value.metadata["ct"]
def gen_value():
raise NotImplementedError()
def async_creator(key, mutex):
mutexes[key] = mutex
if expiration_time is None:
expiration_time = self.expiration_time
mutexes = {}
sorted_unique_keys = sorted(set(keys))
if self.key_mangler:
mangled_keys = [self.key_mangler(k) for k in sorted_unique_keys]
else:
mangled_keys = sorted_unique_keys
orig_to_mangled = dict(zip(sorted_unique_keys, mangled_keys))
values = dict(zip(mangled_keys, self.backend.get_multi(mangled_keys)))
for orig_key, mangled_key in orig_to_mangled.items():
with Lock(
self._mutex(mangled_key),
gen_value,
lambda: get_value(mangled_key),
expiration_time,
async_creator=lambda mutex:
async_creator(orig_key, mutex)):
pass
try:
if mutexes:
# sort the keys, the idea is to prevent deadlocks.
# though haven't been able to simulate one anyway.
keys_to_get = sorted(mutexes)
new_values = creator(*keys_to_get)
values_w_created = dict(
(orig_to_mangled[k], self._value(v))
for k, v in zip(keys_to_get, new_values)
)
if not should_cache_fn:
self.backend.set_multi(values_w_created)
else:
self.backend.set_multi(dict(
(k, v)
for k, v in values_w_created.items()
if should_cache_fn(v[0])
))
values.update(values_w_created)
return [values[orig_to_mangled[k]].payload for k in keys]
finally:
for mutex in mutexes.values():
mutex.release()
def _value(self, value):
"""Return a :class:`.CachedValue` given a value."""
return CachedValue(value, {
"ct": time.time(),
"v": value_version
})
def set(self, key, value):
"""Place a new value in the cache under the given key."""
if self.key_mangler:
key = self.key_mangler(key)
self.backend.set(key, self._value(value))
def set_multi(self, mapping):
"""Place new values in the cache under the given keys.
.. versionadded:: 0.5.0
"""
if self.key_mangler:
mapping = dict((self.key_mangler(k), self._value(v))
for k, v in mapping.items())
else:
mapping = dict((k, self._value(v)) for k, v in mapping.items())
self.backend.set_multi(mapping)
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 delete_multi(self, keys):
"""Remove multiple values from the cache.
This operation is idempotent (can be called multiple times, or on a
non-existent key, safely)
.. versionadded:: 0.5.0
"""
if self.key_mangler:
keys = map(lambda key: self.key_mangler(key), keys)
self.backend.delete_multi(keys)
def cache_on_arguments(self, namespace=None,
expiration_time=None,
should_cache_fn=None,
to_str=compat.string_type):
"""A function decorator that will cache the return
value of the function using a key derived from the
function itself and its arguments.
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
E.g.::
@someregion.cache_on_arguments()
def generate_something(x, y):
return somedatabase.query(x, y)
The decorated function can then be called normally, where
data will be pulled from the cache region unless a new
value is needed::
result = generate_something(5, 6)
The function is also given an attribute ``invalidate()``, which
provides for invalidation of the value. Pass to ``invalidate()``
the same arguments you'd pass to the function itself to represent
a particular value::
generate_something.invalidate(5, 6)
Another attribute ``set()`` is added to provide extra caching
possibilities relative to the function. This is a convenience
method for :meth:`.CacheRegion.set` which will store a given
value directly without calling the decorated function.
The value to be cached is passed as the first argument, and the
arguments which would normally be passed to the function
should follow::
generate_something.set(3, 5, 6)
The above example is equivalent to calling ``generate_something(5, 6)``,
if the function were to produce the value ``3`` as the value to be
cached.
.. versionadded:: 0.4.1 Added ``set()`` method to decorated function.
Similar to ``set()`` is ``refresh()``. This attribute will
invoke the decorated function and populate a new value into
the cache with the new value, as well as returning that value::
newvalue = generate_something.refresh(5, 6)
.. versionadded:: 0.5.0 Added ``refresh()`` method to decorated
function.
The default key generation will use the name
of the function, the module name for the function,
the arguments passed, as well as an optional "namespace"
parameter in order to generate a cache key.
Given a function ``one`` inside the module
``myapp.tools``::
@region.cache_on_arguments(namespace="foo")
def one(a, b):
return a + b
Above, calling ``one(3, 4)`` will produce a
cache key as follows::
myapp.tools:one|foo|3 4
The key generator will ignore an initial argument
of ``self`` or ``cls``, making the decorator suitable
(with caveats) for use with instance or class methods.
Given the example::
class MyClass(object):
@region.cache_on_arguments(namespace="foo")
def one(self, a, b):
return a + b
The cache key above for ``MyClass().one(3, 4)`` will
again produce the same cache key of ``myapp.tools:one|foo|3 4`` -
the name ``self`` is skipped.
The ``namespace`` parameter is optional, and is used
normally to disambiguate two functions of the same
name within the same module, as can occur when decorating
instance or class methods as below::
class MyClass(object):
@region.cache_on_arguments(namespace='MC')
def somemethod(self, x, y):
""
class MyOtherClass(object):
@region.cache_on_arguments(namespace='MOC')
def somemethod(self, x, y):
""
Above, the ``namespace`` parameter disambiguates
between ``somemethod`` on ``MyClass`` and ``MyOtherClass``.
Python class declaration mechanics otherwise prevent
the decorator from having awareness of the ``MyClass``
and ``MyOtherClass`` names, as the function is received
by the decorator before it becomes an instance method.
The function key generation can be entirely replaced
on a per-region basis using the ``function_key_generator``
argument present on :func:`.make_region` and
:class:`.CacheRegion`. If defaults to
:func:`.function_key_generator`.
:param namespace: optional string argument which will be
established as part of the cache key. This may be needed
to disambiguate functions of the same name within the same
source file, such as those
associated with classes - note that the decorator itself
can't see the parent class on a function as the class is
being declared.
:param expiration_time: if not None, will override the normal
expiration time.
May be specified as a callable, taking no arguments, that
returns a value to be used as the ``expiration_time``. This callable
will be called whenever the decorated function itself is called, in
caching or retrieving. Thus, this can be used to
determine a *dynamic* expiration time for the cached function
result. Example use cases include "cache the result until the
end of the day, week or time period" and "cache until a certain date
or time passes".
.. versionchanged:: 0.5.0
``expiration_time`` may be passed as a callable to
:meth:`.CacheRegion.cache_on_arguments`.
:param should_cache_fn: passed to :meth:`.CacheRegion.get_or_create`.
.. versionadded:: 0.4.3
:param to_str: callable, will be called on each function argument
in order to convert to a string. Defaults to ``str()``. If the
function accepts non-ascii unicode arguments on Python 2.x, the
``unicode()`` builtin can be substituted, but note this will
produce unicode cache keys which may require key mangling before
reaching the cache.
.. versionadded:: 0.5.0
.. seealso::
:meth:`.CacheRegion.cache_multi_on_arguments`
:meth:`.CacheRegion.get_or_create`
"""
expiration_time_is_callable = compat.callable(expiration_time)
def decorator(fn):
if to_str is compat.string_type:
# backwards compatible
key_generator = self.function_key_generator(namespace, fn)
else:
key_generator = self.function_key_generator(namespace, fn,
to_str=to_str)
@wraps(fn)
def decorate(*arg, **kw):
key = key_generator(*arg, **kw)
@wraps(fn)
def creator():
return fn(*arg, **kw)
timeout = expiration_time() if expiration_time_is_callable \
else expiration_time
return self.get_or_create(key, creator, timeout,
should_cache_fn)
def invalidate(*arg, **kw):
key = key_generator(*arg, **kw)
self.delete(key)
def set_(value, *arg, **kw):
key = key_generator(*arg, **kw)
self.set(key, value)
def refresh(*arg, **kw):
key = key_generator(*arg, **kw)
value = fn(*arg, **kw)
self.set(key, value)
return value
decorate.set = set_
decorate.invalidate = invalidate
decorate.refresh = refresh
return decorate
return decorator
def cache_multi_on_arguments(self, namespace=None, expiration_time=None,
should_cache_fn=None,
asdict=False, to_str=compat.string_type):
"""A function decorator that will cache multiple return
values from the function using a sequence of keys derived from the
function itself and the arguments passed to it.
This method is the "multiple key" analogue to the
:meth:`.CacheRegion.cache_on_arguments` method.
Example::
@someregion.cache_multi_on_arguments()
def generate_something(*keys):
return [
somedatabase.query(key)
for key in keys
]
The decorated function can be called normally. The decorator
will produce a list of cache keys using a mechanism similar to that
of :meth:`.CacheRegion.cache_on_arguments`, combining the name
of the function with the optional namespace and with the string form
of each key. It will then consult the cache using the same mechanism as that
of :meth:`.CacheRegion.get_multi` to retrieve all current values;
the originally passed keys corresponding to those values which
aren't generated or need regeneration will
be assembled into a new argument list, and the decorated function
is then called with that subset of arguments.
The returned result is a list::
result = generate_something("key1", "key2", "key3")
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create_multi` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
Unlike the :meth:`.CacheRegion.cache_on_arguments`
method, :meth:`.CacheRegion.cache_multi_on_arguments` works only
with a single function signature, one which takes a simple list of keys as
arguments.
Like :meth:`.CacheRegion.cache_on_arguments`, the decorated function
is also provided with a ``set()`` method, which here accepts a
mapping of keys and values to set in the cache::
generate_something.set({"k1": "value1",
"k2": "value2", "k3": "value3"})
an ``invalidate()`` method, which has the effect of deleting
the given sequence of keys using the same mechanism as that of
:meth:`.CacheRegion.delete_multi`::
generate_something.invalidate("k1", "k2", "k3")
and finally a ``refresh()`` method, which will call the creation
function, cache the new values, and return them::
values = generate_something.refresh("k1", "k2", "k3")
Parameters passed to :meth:`.CacheRegion.cache_multi_on_arguments`
have the same meaning as those passed to
:meth:`.CacheRegion.cache_on_arguments`.
:param namespace: optional string argument which will be
established as part of each cache key.
:param expiration_time: if not None, will override the normal
expiration time. May be passed as an integer or a
callable.
:param should_cache_fn: passed to :meth:`.CacheRegion.get_or_create_multi`.
This function is given a value as returned by the creator, and only
if it returns True will that value be placed in the cache.
:param asdict: if ``True``, the decorated function should return
its result as a dictionary of keys->values, and the final result
of calling the decorated function will also be a dictionary.
If left at its default value of ``False``, the decorated function
should return its result as a list of values, and the final
result of calling the decorated function will also be a list.
When ``asdict==True`` if the dictionary returned by the decorated
function is missing keys, those keys will not be cached.
:param to_str: callable, will be called on each function argument
in order to convert to a string. Defaults to ``str()``. If the
function accepts non-ascii unicode arguments on Python 2.x, the
``unicode()`` builtin can be substituted, but note this will
produce unicode cache keys which may require key mangling before
reaching the cache.
.. versionadded:: 0.5.0
.. seealso::
:meth:`.CacheRegion.cache_on_arguments`
:meth:`.CacheRegion.get_or_create_multi`
"""
expiration_time_is_callable = compat.callable(expiration_time)
def decorator(fn):
key_generator = self.function_multi_key_generator(namespace, fn,
to_str=to_str)
@wraps(fn)
def decorate(*arg, **kw):
cache_keys = arg
keys = key_generator(*arg, **kw)
key_lookup = dict(zip(keys, cache_keys))
@wraps(fn)
def creator(*keys_to_create):
return fn(*[key_lookup[k] for k in keys_to_create])
timeout = expiration_time() if expiration_time_is_callable \
else expiration_time
if asdict:
def dict_create(*keys):
d_values = creator(*keys)
return [d_values.get(key_lookup[k], NO_VALUE) for k in keys]
def wrap_cache_fn(value):
if value is NO_VALUE:
return False
elif not should_cache_fn:
return True
else:
return should_cache_fn(value)
result = self.get_or_create_multi(keys, dict_create, timeout,
wrap_cache_fn)
result = dict((k, v) for k, v in zip(cache_keys, result)
if v is not NO_VALUE)
else:
result = self.get_or_create_multi(keys, creator, timeout,
should_cache_fn)
return result
def invalidate(*arg):
keys = key_generator(*arg)
self.delete_multi(keys)
def set_(mapping):
keys = list(mapping)
gen_keys = key_generator(*keys)
self.set_multi(dict(
(gen_key, mapping[key])
for gen_key, key
in zip(gen_keys, keys))
)
def refresh(*arg):
keys = key_generator(*arg)
values = fn(*arg)
if asdict:
self.set_multi(
dict(zip(keys, [values[a] for a in arg]))
)
return values
else:
self.set_multi(
dict(zip(keys, values))
)
return values
decorate.set = set_
decorate.invalidate = invalidate
decorate.refresh = refresh
return decorate
return decorator
def configure(self, backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None,
wrap=None
):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. May be passed as an integer number
of seconds, or as a ``datetime.timedelta`` value.
.. versionadded 0.5.0
``expiration_time`` may be optionally passed as a
``datetime.timedelta`` value.
The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
: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 :class:`.ProxyBackend`
classes and/or instances, each of which will be applied
in a chain to ultimately wrap the original backend,
so that custom functionality augmentation can be applied.
.. versionadded:: 0.5.0
.. seealso::
:ref:`changing_backend_behavior`
"""
if "backend" in self.__dict__:
raise Exception(
"This region is already "
"configured with backend: %s"
% 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(expiration_time.total_seconds())
else:
raise Exception('expiration_time is not a number or timedelta.')
if self.key_mangler is None:
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
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):
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(
"dogpile.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]
)
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 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``.
"""
def __init__(self,
name=None,
function_key_generator=function_key_generator,
key_mangler=None):
"""Construct a new :class:`.CacheRegion`."""
self.function_key_generator = function_key_generator
if key_mangler:
self.key_mangler = key_mangler
else:
self.key_mangler = None
self._invalidated = None
def configure(self,
backend,
expiration_time=None,
arguments=None,
_config_argument_dict=None,
_config_prefix=None):
"""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 ``dogpile.cache`` entrypoint.
:param expiration_time: Optional. The expiration time passed
to the dogpile system. The :meth:`.CacheRegion.get_or_create`
method as well as the :meth:`.CacheRegion.cache_on_arguments`
decorator (though note: **not** the :meth:`.CacheRegion.get`
method) will call upon the value creation function after this
time period has passed since the last generation.
:param arguments: Optional. The structure here is passed
directly to the constructor of the :class:`.CacheBackend`
in use, though is typically a dictionary.
"""
if "backend" in self.__dict__:
raise Exception("This region is already "
"configured with backend: %s" % 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 {})
self.expiration_time = expiration_time
if self.key_mangler is None:
self.key_mangler = self.backend.key_mangler
self._lock_registry = NameRegistry(self._create_mutex)
return self
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 invalidate(self):
"""Invalidate this :class:`.CacheRegion`.
Invalidation works by setting a current timestamp
(using ``time.time()``)
representing the "minimum creation time" for
a value. Any retrieved value whose creation
time is prior to this timestamp
is considered to be stale. It does not
affect the data in the cache in any way, and is also
local to this instance of :class:`.CacheRegion`.
Once set, the invalidation time is honored by
the :meth:`.CacheRegion.get_or_create` and
:meth:`.CacheRegion.get` methods.
.. versionadded:: 0.3.0
"""
self._invalidated = time.time()
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":"dogpile.cache.dbm",
"cache.local.arguments.filename":"/path/to/dbmfile.dbm",
"cache.memcached.backend":"dogpile.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)
@memoized_property
def backend(self):
raise Exception("No backend is configured on this region.")
def get(self, key, expiration_time=None, ignore_expiration=False):
"""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``.
By default, the configured expiration time of the
:class:`.CacheRegion`, or alternatively the expiration
time supplied by the ``expiration_time`` argument,
is tested against the creation time of the retrieved
value versus the current time (as reported by ``time.time()``).
If stale, the cached value is ignored and the ``NO_VALUE``
token is returned. Passing the flag ``ignore_expiration=True``
bypasses the expiration time check.
.. versionchanged:: 0.3.0
:meth:`.CacheRegion.get` now checks the value's creation time
against the expiration time, rather than returning
the value unconditionally.
The method also interprets the cached value in terms
of the current "invalidation" time as set by
the :meth:`.invalidate` method. If a value is present,
but its creation time is older than the current
invalidation time, the ``NO_VALUE`` token is returned.
Passing the flag ``ignore_expiration=True`` bypasses
the invalidation time check.
.. versionadded:: 0.3.0
Support for the :meth:`.CacheRegion.invalidate`
method.
: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.
:param expiration_time: Optional expiration time value
which will supersede that configured on the :class:`.CacheRegion`
itself.
.. versionadded:: 0.3.0
:param ignore_expiration: if ``True``, the value is returned
from the cache if present, regardless of configured
expiration times or whether or not :meth:`.invalidate`
was called.
.. versionadded:: 0.3.0
"""
if self.key_mangler:
key = self.key_mangler(key)
value = self.backend.get(key)
if value is NO_VALUE:
return value
elif not ignore_expiration:
if expiration_time is None:
expiration_time = self.expiration_time
if expiration_time is not None and \
time.time() - value.metadata["ct"] > expiration_time:
return NO_VALUE
elif self._invalidated and value.metadata["ct"] < self._invalidated:
return NO_VALUE
return value.payload
def get_or_create(self, key, creator, expiration_time=None):
"""Return a cached value based on the given key.
If the value does not exist or is considered to be expired
based on its creation time, the given
creation function may or may not be used to recreate the value
and persist the newly generated value in the cache.
Whether or not the function is used depends on if the
*dogpile lock* can be acquired or not. If it can't, it means
a different thread or process is already running a creation
function for this key against the cache. When the dogpile
lock cannot be acquired, the method will block if no
previous value is available, until the lock is released and
a new value available. If a previous value
is available, that value is returned immediately without blocking.
If the :meth:`.invalidate` method has been called, and
the retrieved value's timestamp is older than the invalidation
timestamp, the value is unconditionally prevented from
being returned. The method will attempt to acquire the dogpile
lock to generate a new value, or will wait
until the lock is released to return the new value.
.. versionchanged:: 0.3.0
The value is unconditionally regenerated if the creation
time is older than the last call to :meth:`.invalidate`.
: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.
:param creator: function which creates a new value.
:param expiration_time: optional expiration time which will overide
the expiration time already configured on this :class:`.CacheRegion`
if not None. To set no expiration, use the value -1.
See also:
:meth:`.CacheRegion.cache_on_arguments` - applies :meth:`.get_or_create`
to any function using a decorator.
"""
if self.key_mangler:
key = self.key_mangler(key)
def get_value():
value = self.backend.get(key)
if value is NO_VALUE or \
value.metadata['v'] != value_version or \
(self._invalidated and
value.metadata["ct"] < self._invalidated):
raise NeedRegenerationException()
return value.payload, value.metadata["ct"]
def gen_value():
value = self._value(creator())
self.backend.set(key, value)
return value.payload, value.metadata["ct"]
if expiration_time is None:
expiration_time = self.expiration_time
with Lock(self._mutex(key), gen_value, get_value,
expiration_time) as value:
return value
def _value(self, value):
"""Return a :class:`.CachedValue` given a value."""
return CachedValue(value, {"ct": time.time(), "v": value_version})
def set(self, key, value):
"""Place a new value in the cache under the given key."""
if self.key_mangler:
key = self.key_mangler(key)
self.backend.set(key, self._value(value))
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 cache_on_arguments(self, namespace=None, expiration_time=None):
"""A function decorator that will cache the return
value of the function using a key derived from the
function itself and its arguments.
The decorator internally makes use of the
:meth:`.CacheRegion.get_or_create` method to access the
cache and conditionally call the function. See that
method for additional behavioral details.
E.g.::
@someregion.cache_on_arguments()
def generate_something(x, y):
return somedatabase.query(x, y)
The decorated function can then be called normally, where
data will be pulled from the cache region unless a new
value is needed::
result = generate_something(5, 6)
The function is also given an attribute ``invalidate``, which
provides for invalidation of the value. Pass to ``invalidate()``
the same arguments you'd pass to the function itself to represent
a particular value::
generate_something.invalidate(5, 6)
Another attribute ``set`` is added to provide extra caching
possibilities relative to the function. This is a convenience
method for :meth:`.CacheRegion.set` which will store a given
value directly without calling the decorated function.
The value to be cached is passed as the first argument, and the
arguments which would normally be passed to the function
should follow::
generate_something.set(3, 5, 6)
The above example is equivalent to calling ``generate_something(5, 6)``,
if the function were to produce the value ``3`` as the value to be
cached.
.. versionadded:: 0.4.1 Added set() method to decorated function.
The default key generation will use the name
of the function, the module name for the function,
the arguments passed, as well as an optional "namespace"
parameter in order to generate a cache key.
Given a function ``one`` inside the module
``myapp.tools``::
@region.cache_on_arguments(namespace="foo")
def one(a, b):
return a + b
Above, calling ``one(3, 4)`` will produce a
cache key as follows::
myapp.tools:one|foo|3 4
The key generator will ignore an initial argument
of ``self`` or ``cls``, making the decorator suitable
(with caveats) for use with instance or class methods.
Given the example::
class MyClass(object):
@region.cache_on_arguments(namespace="foo")
def one(self, a, b):
return a + b
The cache key above for ``MyClass().one(3, 4)`` will
again produce the same cache key of ``myapp.tools:one|foo|3 4`` -
the name ``self`` is skipped.
The ``namespace`` parameter is optional, and is used
normally to disambiguate two functions of the same
name within the same module, as can occur when decorating
instance or class methods as below::
class MyClass(object):
@region.cache_on_arguments(namespace='MC')
def somemethod(self, x, y):
""
class MyOtherClass(object):
@region.cache_on_arguments(namespace='MOC')
def somemethod(self, x, y):
""
Above, the ``namespace`` parameter disambiguates
between ``somemethod`` on ``MyClass`` and ``MyOtherClass``.
Python class declaration mechanics otherwise prevent
the decorator from having awareness of the ``MyClass``
and ``MyOtherClass`` names, as the function is received
by the decorator before it becomes an instance method.
The function key generation can be entirely replaced
on a per-region basis using the ``function_key_generator``
argument present on :func:`.make_region` and
:class:`.CacheRegion`. If defaults to
:func:`.function_key_generator`.
:param namespace: optional string argument which will be
established as part of the cache key. This may be needed
to disambiguate functions of the same name within the same
source file, such as those
associated with classes - note that the decorator itself
can't see the parent class on a function as the class is
being declared.
:param expiration_time: if not None, will override the normal
expiration time.
"""
def decorator(fn):
key_generator = self.function_key_generator(namespace, fn)
@wraps(fn)
def decorate(*arg, **kw):
key = key_generator(*arg, **kw)
def creator():
return fn(*arg, **kw)
return self.get_or_create(key, creator, expiration_time)
def invalidate(*arg, **kw):
key = key_generator(*arg, **kw)
self.delete(key)
def set_(value, *arg, **kw):
key = key_generator(*arg, **kw)
self.set(key, value)
decorate.set = set_
decorate.invalidate = invalidate
return decorate
return decorator