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region.py
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from __future__ import annotations import contextlib import datetime from functools import partial from functools import wraps import json import logging from numbers import Number import threading import time from typing import Any from typing import Callable from typing import cast from typing import Mapping from typing import Optional from typing import Sequence from typing import Tuple from typing import Type from typing import TYPE_CHECKING from typing import Union from decorator import decorate from . import exception from .api import BackendArguments from .api import BackendFormatted from .api import CachedValue from .api import CacheMutex from .api import CacheReturnType from .api import CantDeserializeException from .api import KeyType from .api import MetaDataType from .api import NO_VALUE from .api import NoValueType from .api import SerializedReturnType from .api import Serializer from .api import ValuePayload from .backends import _backend_loader from .backends import register_backend # noqa from .proxy import ProxyBackend from .util import function_key_generator from .util import function_multi_key_generator from .util import repr_obj from .. import Lock from .. import NeedRegenerationException from ..util import coerce_string_conf from ..util import memoized_property from ..util import NameRegistry from ..util import PluginLoader from ..util.typing import Self value_version = 2 """An integer placed in the :class:`.CachedValue` so that new versions of dogpile.cache can detect cached values from a previous, backwards-incompatible version. """ log = logging.getLogger(__name__) AsyncCreator = Callable[ ["CacheRegion", KeyType, Callable[[], ValuePayload], CacheMutex], None ] ExpirationTimeCallable = Callable[[], float] ToStr = Callable[[Any], str] FunctionKeyGenerator = Callable[..., Callable[..., KeyType]] FunctionMultiKeyGenerator = Callable[..., Callable[..., Sequence[KeyType]]] class RegionInvalidationStrategy: """Region invalidation strategy interface Implement this interface and pass implementation instance to :meth:`.CacheRegion.configure` to override default region invalidation. Example:: class CustomInvalidationStrategy(RegionInvalidationStrategy): def __init__(self): self._soft_invalidated = None self._hard_invalidated = None def invalidate(self, hard=None): if hard: self._soft_invalidated = None self._hard_invalidated = time.time() else: self._soft_invalidated = time.time() self._hard_invalidated = None def is_invalidated(self, timestamp): return ((self._soft_invalidated and timestamp < self._soft_invalidated) or (self._hard_invalidated and timestamp < self._hard_invalidated)) def was_hard_invalidated(self): return bool(self._hard_invalidated) def is_hard_invalidated(self, timestamp): return (self._hard_invalidated and timestamp < self._hard_invalidated) def was_soft_invalidated(self): return bool(self._soft_invalidated) def is_soft_invalidated(self, timestamp): return (self._soft_invalidated and timestamp < self._soft_invalidated) The custom implementation is injected into a :class:`.CacheRegion` at configure time using the :paramref:`.CacheRegion.configure.region_invalidator` parameter:: region = CacheRegion() region = region.configure(region_invalidator=CustomInvalidationStrategy()) # noqa Invalidation strategies that wish to have access to the :class:`.CacheRegion` itself should construct the invalidator given the region as an argument:: class MyInvalidator(RegionInvalidationStrategy): def __init__(self, region): self.region = region # ... # ... region = CacheRegion() region = region.configure(region_invalidator=MyInvalidator(region)) .. versionadded:: 0.6.2 .. seealso:: :paramref:`.CacheRegion.configure.region_invalidator` """ def invalidate(self, hard: bool = True) -> None: """Region invalidation. :class:`.CacheRegion` propagated call. The default invalidation system works by setting a current timestamp (using ``time.time()``) to consider all older timestamps effectively invalidated. """ raise NotImplementedError() def is_hard_invalidated(self, timestamp: float) -> bool: """Check timestamp to determine if it was hard invalidated. :return: Boolean. True if ``timestamp`` is older than the last region invalidation time and region is invalidated in hard mode. """ raise NotImplementedError() def is_soft_invalidated(self, timestamp: float) -> bool: """Check timestamp to determine if it was soft invalidated. :return: Boolean. True if ``timestamp`` is older than the last region invalidation time and region is invalidated in soft mode. """ raise NotImplementedError() def is_invalidated(self, timestamp: float) -> bool: """Check timestamp to determine if it was invalidated. :return: Boolean. True if ``timestamp`` is older than the last region invalidation time. """ raise NotImplementedError() def was_soft_invalidated(self) -> bool: """Indicate the region was invalidated in soft mode. :return: Boolean. True if region was invalidated in soft mode. """ raise NotImplementedError() def was_hard_invalidated(self) -> bool: """Indicate the region was invalidated in hard mode. :return: Boolean. True if region was invalidated in hard mode. """ raise NotImplementedError() class DefaultInvalidationStrategy(RegionInvalidationStrategy): def __init__(self): self._is_hard_invalidated = None self._invalidated = None def invalidate(self, hard: bool = True) -> None: self._is_hard_invalidated = bool(hard) self._invalidated = time.time() def is_invalidated(self, timestamp: float) -> bool: return self._invalidated is not None and timestamp < self._invalidated def was_hard_invalidated(self) -> bool: return self._is_hard_invalidated is True def is_hard_invalidated(self, timestamp: float) -> bool: return self.was_hard_invalidated() and self.is_invalidated(timestamp) def was_soft_invalidated(self) -> bool: return self._is_hard_invalidated is False def is_soft_invalidated(self, timestamp: float) -> bool: return self.was_soft_invalidated() and self.is_invalidated(timestamp) class CacheRegion: r"""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() .. seealso:: :func:`.function_key_generator` - default key generator :func:`.kwarg_function_key_generator` - optional gen that also uses keyword arguments :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 serializer: function which will be applied to all values before passing to the backend. Defaults to ``None``, in which case the serializer recommended by the backend will be used. Typical serializers include ``pickle.dumps`` and ``json.dumps``. .. versionadded:: 1.1.0 :param deserializer: function which will be applied to all values returned by the backend. Defaults to ``None``, in which case the deserializer recommended by the backend will be used. Typical deserializers include ``pickle.dumps`` and ``json.dumps``. Deserializers can raise a :class:`.api.CantDeserializeException` if they are unable to deserialize the value from the backend, indicating deserialization failed and that caching should proceed to re-generate a value. This allows an application that has been updated to gracefully re-cache old items which were persisted by a previous version of the application and can no longer be successfully deserialized. .. versionadded:: 1.1.0 added "deserializer" parameter .. versionadded:: 1.2.0 added support for :class:`.api.CantDeserializeException` :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: Optional[str] = None, function_key_generator: FunctionKeyGenerator = function_key_generator, function_multi_key_generator: FunctionMultiKeyGenerator = function_multi_key_generator, # noqa E501 key_mangler: Optional[Callable[[KeyType], KeyType]] = None, serializer: Optional[Callable[[ValuePayload], bytes]] = None, deserializer: Optional[Callable[[bytes], ValuePayload]] = None, async_creation_runner: Optional[AsyncCreator] = 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.serializer = self._user_defined_serializer = serializer self.deserializer = self._user_defined_deserializer = deserializer self.async_creation_runner = async_creation_runner self.region_invalidator: RegionInvalidationStrategy = ( DefaultInvalidationStrategy() ) def configure( self, backend: str, expiration_time: Optional[Union[float, datetime.timedelta]] = None, arguments: Optional[BackendArguments] = None, _config_argument_dict: Optional[Mapping[str, Any]] = None, _config_prefix: Optional[str] = None, wrap: Sequence[Union[ProxyBackend, Type[ProxyBackend]]] = (), replace_existing_backend: bool = False, region_invalidator: Optional[RegionInvalidationStrategy] = None, ) -> Self: """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 :param region_invalidator: Optional. Override default invalidation strategy with custom implementation of :class:`.RegionInvalidationStrategy`. .. versionadded:: 0.6.2 """ 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 ) try: backend_cls = _backend_loader.load(backend) except PluginLoader.NotFound: raise exception.PluginNotFound( "Couldn't find cache plugin to load: %s" % 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: Union[float, None] if not expiration_time or isinstance(expiration_time, Number): self.expiration_time = cast(Union[None, float], expiration_time) elif isinstance(expiration_time, datetime.timedelta): self.expiration_time = int(expiration_time.total_seconds()) 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 if not self._user_defined_serializer: self.serializer = self.backend.serializer if not self._user_defined_deserializer: self.deserializer = self.backend.deserializer self._lock_registry = NameRegistry(self._create_mutex) if getattr(wrap, "__iter__", False): for wrapper in reversed(wrap): self.wrap(wrapper) if region_invalidator: self.region_invalidator = region_invalidator return self def wrap(self, proxy: Union[ProxyBackend, Type[ProxyBackend]]) -> None: """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 isinstance(proxy, type): proxy_instance = proxy() else: proxy_instance = proxy if not isinstance(proxy_instance, ProxyBackend): raise TypeError( "%r is not a valid ProxyBackend" % (proxy_instance,) ) self.backend = proxy_instance.wrap(self.backend) def _mutex(self, key): return self._lock_registry.get(key) class _LockWrapper(CacheMutex): """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 locked(self): return self.lock.locked() def _create_mutex(self, key): mutex = self.backend.get_mutex(key) if mutex is not None: return mutex else: return self._LockWrapper() # cached value _actual_backend = None @property def actual_backend(self): """Return the ultimate backend underneath any proxies. The backend might be the result of one or more ``proxy.wrap`` applications. If so, derive the actual underlying backend. .. versionadded:: 0.6.6 """ if self._actual_backend is None: _backend = self.backend while hasattr(_backend, "proxied"): _backend = _backend.proxied self._actual_backend = _backend return self._actual_backend def invalidate(self, hard=True): """Invalidate this :class:`.CacheRegion`. The default invalidation system 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 **local to this instance of :class:`.CacheRegion`.** .. warning:: The :meth:`.CacheRegion.invalidate` method's default mode of operation is to set a timestamp **local to this CacheRegion in this Python process only**. It does not impact other Python processes or regions as the timestamp is **only stored locally in memory**. To implement invalidation where the timestamp is stored in the cache or similar so that all Python processes can be affected by an invalidation timestamp, implement a custom :class:`.RegionInvalidationStrategy`. 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 """ self.region_invalidator.invalidate(hard) 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), replace_existing_backend=config_dict.get( "%sreplace_existing_backend" % prefix, False ), ) @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: KeyType, expiration_time: Optional[float] = None, ignore_expiration: bool = False, ) -> Union[ValuePayload, NoValueType]: """Return a value from the cache, based on the given key. If the value is not present, the method returns the token :data:`.api.NO_VALUE`. :data:`.api.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 :data:`.api.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 :data:`.api.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. .. note:: The :paramref:`.CacheRegion.get.expiration_time` argument is **not persisted in the cache** and is relevant only to **this specific cache retrieval operation**, relative to the creation time stored with the existing cached value. Subsequent calls to :meth:`.CacheRegion.get` are **not** affected by this value. .. 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 .. seealso:: :meth:`.CacheRegion.get_multi` :meth:`.CacheRegion.get_or_create` :meth:`.CacheRegion.set` :meth:`.CacheRegion.delete` """ value = self._get_cache_value(key, expiration_time, ignore_expiration) return value.payload def get_value_metadata( self, key: KeyType, expiration_time: Optional[float] = None, ignore_expiration: bool = False, ) -> Optional[CachedValue]: """Return the :class:`.CachedValue` object directly from the cache. This is the enclosing datastructure that includes the value as well as the metadata, including the timestamp when the value was cached. Convenience accessors on :class:`.CachedValue` also provide for common data such as :attr:`.CachedValue.cached_time` and :attr:`.CachedValue.age`. .. versionadded:: 1.3. Added :meth:`.CacheRegion.get_value_metadata` """ cache_value = self._get_cache_value( key, expiration_time, ignore_expiration ) if cache_value is NO_VALUE: return None else: if TYPE_CHECKING: assert isinstance(cache_value, CachedValue) return cache_value def _get_cache_value( self, key: KeyType, expiration_time: Optional[float] = None, ignore_expiration: bool = False, ) -> CacheReturnType: if self.key_mangler: key = self.key_mangler(key) value = self._get_from_backend(key) value = self._unexpired_value_fn(expiration_time, ignore_expiration)( value ) return value 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.region_invalidator.is_invalidated( value.metadata["ct"] ): 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 is not None: keys = [self.key_mangler(key) for key in keys] backend_values = self._get_multi_from_backend(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 ) ] @contextlib.contextmanager def _log_time(self, keys): start_time = time.time() yield seconds = time.time() - start_time log.debug( "Cache value generated in %(seconds).3f seconds for key(s): " "%(keys)r", {"seconds": seconds, "keys": repr_obj(keys)}, ) def _is_cache_miss(self, value, orig_key): if value is NO_VALUE: log.debug("No value present for key: %r", orig_key) elif value.metadata["v"] != value_version: log.debug("Dogpile version update for key: %r", orig_key) elif self.region_invalidator.is_hard_invalidated(value.metadata["ct"]): log.debug("Hard invalidation detected for key: %r", orig_key) else: return False return True def key_is_locked(self, key: KeyType) -> bool: """Return True if a particular cache key is currently being generated within the dogpile lock. .. versionadded:: 1.1.2 """ mutex = self._mutex(key) locked: bool = mutex.locked() return locked def get_or_create( self, key: KeyType, creator: Callable[..., ValuePayload], expiration_time: Optional[float] = None, should_cache_fn: Optional[Callable[[ValuePayload], bool]] = None, creator_args: Optional[Tuple[Any, Mapping[str, Any]]] = None, ) -> ValuePayload: """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 creator_args: optional tuple of (args, kwargs) that will be passed to the creator function if present. .. versionadded:: 0.7.0 :param expiration_time: optional expiration time which will override the expiration time already configured on this :class:`.CacheRegion` if not None. To set no expiration, use the value -1. .. note:: The :paramref:`.CacheRegion.get_or_create.expiration_time` argument is **not persisted in the cache** and is relevant only to **this specific cache retrieval operation**, relative to the creation time stored with the existing cached value. Subsequent calls to :meth:`.CacheRegion.get_or_create` are **not** affected by this value. :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.get` :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._get_from_backend(key) if self._is_cache_miss(value, orig_key): raise NeedRegenerationException() ct = cast(CachedValue, value).metadata["ct"] if self.region_invalidator.is_soft_invalidated(ct): if expiration_time is None: raise exception.DogpileCacheException( "Non-None expiration time required " "for soft invalidation" ) ct = time.time() - expiration_time - 0.0001 return value.payload, ct def gen_value(): with self._log_time(orig_key): if creator_args: created_value = creator( *creator_args[0], **creator_args[1] ) else: created_value = creator() value = self._value(created_value) if ( expiration_time is None and self.region_invalidator.was_soft_invalidated() ): raise exception.DogpileCacheException( "Non-None expiration time required " "for soft invalidation" ) if not should_cache_fn or should_cache_fn(created_value): self._set_cached_value_to_backend(key, value) return value.payload, value.metadata["ct"] if expiration_time is None: expiration_time = self.expiration_time if expiration_time == -1: expiration_time = None async_creator: Optional[Callable[[CacheMutex], AsyncCreator]] if self.async_creation_runner: acr = self.async_creation_runner def async_creator(mutex): if creator_args: ca = creator_args @wraps(creator) def go(): return creator(*ca[0], **ca[1]) else: go = creator # type: ignore return acr(self, orig_key, go, 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: Sequence[KeyType], creator: Callable[[], ValuePayload], expiration_time: Optional[float] = None, should_cache_fn: Optional[Callable[[ValuePayload], bool]] = None, ) -> Sequence[ValuePayload]: """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 override 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 self._is_cache_miss(value, orig_key): # 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 = cast(CachedValue, value).metadata["ct"] if self.region_invalidator.is_soft_invalidated(ct): if expiration_time is None: raise exception.DogpileCacheException( "Non-None expiration time required " "for soft invalidation" ) ct = time.time() - expiration_time - 0.0001 return value.payload, ct def gen_value() -> ValuePayload: raise NotImplementedError() def async_creator(mutexes, key, mutex): mutexes[key] = mutex if expiration_time is None: expiration_time = self.expiration_time if expiration_time == -1: expiration_time = None 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._get_multi_from_backend(mangled_keys)) ) mutexes: Mapping[KeyType, Any] = {} 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( mutexes, 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) with self._log_time(keys_to_get): new_values = creator(*keys_to_get) values_w_created = { orig_to_mangled[k]: self._value(v) for k, v in zip(keys_to_get, new_values) } if ( expiration_time is None and self.region_invalidator.was_soft_invalidated() ): raise exception.DogpileCacheException( "Non-None expiration time required " "for soft invalidation" ) if not should_cache_fn: self._set_multi_cached_value_to_backend(values_w_created) else: self._set_multi_cached_value_to_backend( { k: v for k, v in values_w_created.items() if should_cache_fn(v.payload) } ) 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: Any, metadata: Optional[MetaDataType] = None ) -> CachedValue: """Return a :class:`.CachedValue` given a value.""" if metadata is None: metadata = self._gen_metadata() return CachedValue(value, metadata) def _parse_serialized_from_backend( self, value: SerializedReturnType ) -> CacheReturnType: if value in (None, NO_VALUE): return NO_VALUE assert self.deserializer byte_value = cast(bytes, value) bytes_metadata, _, bytes_payload = byte_value.partition(b"|") metadata = json.loads(bytes_metadata) try: payload = self.deserializer(bytes_payload) except CantDeserializeException: return NO_VALUE else: return CachedValue(payload, metadata) def _serialize_cached_value_elements( self, payload: ValuePayload, metadata: MetaDataType ) -> bytes: serializer = cast(Serializer, self.serializer) return b"%b|%b" % ( json.dumps(metadata).encode("ascii"), serializer(payload), ) def _serialized_payload( self, payload: ValuePayload, metadata: Optional[MetaDataType] = None ) -> BackendFormatted: """Return a backend formatted representation of a value. If a serializer is in use then this will return a string representation with the value formatted by the serializer. """ if metadata is None: metadata = self._gen_metadata() return self._serialize_cached_value_elements(payload, metadata) def _serialized_cached_value(self, value: CachedValue) -> BackendFormatted: """Return a backend formatted representation of a :class:`.CachedValue`. If a serializer is in use then this will return a string representation with the value formatted by the serializer. """ assert self.serializer return self._serialize_cached_value_elements( value.payload, value.metadata ) def _get_from_backend(self, key: KeyType) -> CacheReturnType: if self.deserializer: return self._parse_serialized_from_backend( self.backend.get_serialized(key) ) else: return cast(CacheReturnType, self.backend.get(key)) def _get_multi_from_backend( self, keys: Sequence[KeyType] ) -> Sequence[CacheReturnType]: if self.deserializer: return [ self._parse_serialized_from_backend(v) for v in self.backend.get_serialized_multi(keys) ] else: return cast( Sequence[CacheReturnType], self.backend.get_multi(keys) ) def _set_cached_value_to_backend( self, key: KeyType, value: CachedValue ) -> None: if self.serializer: self.backend.set_serialized( key, self._serialized_cached_value(value) ) else: self.backend.set(key, value) def _set_multi_cached_value_to_backend( self, mapping: Mapping[KeyType, CachedValue] ) -> None: if not mapping: return if self.serializer: self.backend.set_serialized_multi( { k: self._serialized_cached_value(v) for k, v in mapping.items() } ) else: self.backend.set_multi(mapping) def _gen_metadata(self) -> MetaDataType: return {"ct": time.time(), "v": value_version} def set(self, key: KeyType, value: ValuePayload) -> None: """Place a new value in the cache under the given key.""" if self.key_mangler: key = self.key_mangler(key) if self.serializer: self.backend.set_serialized(key, self._serialized_payload(value)) else: self.backend.set(key, self._value(value)) def set_multi(self, mapping: Mapping[KeyType, ValuePayload]) -> None: """Place new values in the cache under the given keys.""" if not mapping: return metadata = self._gen_metadata() if self.serializer: if self.key_mangler: mapping = { self.key_mangler(k): self._serialized_payload( v, metadata=metadata ) for k, v in mapping.items() } else: mapping = { k: self._serialized_payload(v, metadata=metadata) for k, v in mapping.items() } self.backend.set_serialized_multi(mapping) else: if self.key_mangler: mapping = { self.key_mangler(k): self._value(v, metadata=metadata) for k, v in mapping.items() } else: mapping = { k: self._value(v, metadata=metadata) for k, v in mapping.items() } self.backend.set_multi(mapping) def delete(self, key: KeyType) -> None: """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: Sequence[KeyType]) -> None: """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: km = self.key_mangler keys = [km(key) for key in keys] self.backend.delete_multi(keys) def cache_on_arguments( self, namespace: Optional[str] = None, expiration_time: Union[float, ExpirationTimeCallable, None] = None, should_cache_fn: Optional[Callable[[ValuePayload], bool]] = None, to_str: Callable[[Any], str] = str, function_key_generator: Optional[FunctionKeyGenerator] = None, ) -> Callable[[Callable[..., ValuePayload]], Callable[..., ValuePayload]]: """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. ``original()`` on other hand will invoke the decorated function without any caching:: newvalue = generate_something.original(5, 6) .. versionadded:: 0.6.0 Added ``original()`` 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: @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: @region.cache_on_arguments(namespace='MC') def somemethod(self, x, y): "" class MyOtherClass: @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". :param should_cache_fn: passed to :meth:`.CacheRegion.get_or_create`. :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. :param function_key_generator: a function that will produce a "cache key". This function will supersede the one configured on the :class:`.CacheRegion` itself. .. seealso:: :meth:`.CacheRegion.cache_multi_on_arguments` :meth:`.CacheRegion.get_or_create` """ expiration_time_is_callable = callable(expiration_time) if function_key_generator is None: _function_key_generator = self.function_key_generator else: _function_key_generator = function_key_generator def get_or_create_for_user_func(key_generator, user_func, *arg, **kw): key = key_generator(*arg, **kw) timeout: Optional[float] = ( cast(ExpirationTimeCallable, expiration_time)() if expiration_time_is_callable else cast(Optional[float], expiration_time) ) return self.get_or_create( key, user_func, timeout, should_cache_fn, (arg, kw) ) def cache_decorator(user_func): if to_str is cast(Callable[[Any], str], str): # backwards compatible key_generator = _function_key_generator( namespace, user_func ) # type: ignore else: key_generator = _function_key_generator( namespace, user_func, to_str ) def refresh(*arg, **kw): """ Like invalidate, but regenerates the value instead """ key = key_generator(*arg, **kw) value = user_func(*arg, **kw) self.set(key, value) return value 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) user_func.set = set_ user_func.invalidate = invalidate user_func.get = get user_func.refresh = refresh user_func.original = user_func # Use `decorate` to preserve the signature of :param:`user_func`. return decorate( user_func, partial(get_or_create_for_user_func, key_generator) ) return cache_decorator def cache_multi_on_arguments( self, namespace: Optional[str] = None, expiration_time: Union[float, ExpirationTimeCallable, None] = None, should_cache_fn: Optional[Callable[[ValuePayload], bool]] = None, asdict: bool = False, to_str: ToStr = str, function_multi_key_generator: Optional[ FunctionMultiKeyGenerator ] = None, ) -> Callable[ [Callable[..., Sequence[ValuePayload]]], Callable[ ..., Union[Sequence[ValuePayload], Mapping[KeyType, ValuePayload]] ], ]: """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 = callable(expiration_time) if function_multi_key_generator is None: _function_multi_key_generator = self.function_multi_key_generator else: _function_multi_key_generator = function_multi_key_generator def get_or_create_for_user_func( key_generator: Callable[..., Sequence[KeyType]], user_func: Callable[..., Sequence[ValuePayload]], *arg: Any, **kw: Any, ) -> Union[Sequence[ValuePayload], Mapping[KeyType, ValuePayload]]: cache_keys = arg keys = key_generator(*arg, **kw) key_lookup = dict(zip(keys, cache_keys)) @wraps(user_func) def creator(*keys_to_create): return user_func(*[key_lookup[k] for k in keys_to_create]) timeout: Optional[float] = ( cast(ExpirationTimeCallable, expiration_time)() if expiration_time_is_callable else cast(Optional[float], expiration_time) ) result: Union[ Sequence[ValuePayload], Mapping[KeyType, ValuePayload] ] 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 cache_decorator(user_func): key_generator = _function_multi_key_generator( namespace, user_func, to_str=to_str ) 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 = user_func(*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 user_func.set = set_ user_func.invalidate = invalidate user_func.refresh = refresh user_func.get = get # Use `decorate` to preserve the signature of :param:`user_func`. return decorate( user_func, partial(get_or_create_for_user_func, key_generator) ) return cache_decorator def make_region(*arg: Any, **kw: Any) -> CacheRegion: """Instantiate a new :class:`.CacheRegion`. Currently, :func:`.make_region` is a passthrough to :class:`.CacheRegion`. See that class for constructor arguments. """ return CacheRegion(*arg, **kw)