Mini Shell
"""
Memcached Backends
------------------
Provides backends for talking to `memcached <http://memcached.org>`_.
"""
import random
import threading
import time
import typing
from typing import Any
from typing import Mapping
import warnings
from ..api import CacheBackend
from ..api import NO_VALUE
from ... import util
if typing.TYPE_CHECKING:
import bmemcached
import memcache
import pylibmc
import pymemcache
else:
# delayed import
bmemcached = None # noqa F811
memcache = None # noqa F811
pylibmc = None # noqa F811
pymemcache = None # noqa F811
__all__ = (
"GenericMemcachedBackend",
"MemcachedBackend",
"PylibmcBackend",
"PyMemcacheBackend",
"BMemcachedBackend",
"MemcachedLock",
)
class MemcachedLock:
"""Simple distributed lock using memcached."""
def __init__(self, client_fn, key, timeout=0):
self.client_fn = client_fn
self.key = "_lock" + key
self.timeout = timeout
self._mutex = threading.Lock()
def acquire(self, wait=True):
client = self.client_fn()
i = 0
while True:
with self._mutex:
if client.add(self.key, 1, self.timeout):
return True
elif not wait:
return False
sleep_time = (((i + 1) * random.random()) + 2**i) / 2.5
time.sleep(sleep_time)
if i < 15:
i += 1
def locked(self):
client = self.client_fn()
return client.get(self.key) is not None
def release(self):
client = self.client_fn()
client.delete(self.key)
class GenericMemcachedBackend(CacheBackend):
"""Base class for memcached backends.
This base class accepts a number of paramters
common to all backends.
:param url: the string URL to connect to. Can be a single
string or a list of strings. This is the only argument
that's required.
:param distributed_lock: boolean, when True, will use a
memcached-lock as the dogpile lock (see :class:`.MemcachedLock`).
Use this when multiple
processes will be talking to the same memcached instance.
When left at False, dogpile will coordinate on a regular
threading mutex.
:param lock_timeout: integer, number of seconds after acquiring a lock that
memcached should expire it. This argument is only valid when
``distributed_lock`` is ``True``.
.. versionadded:: 0.5.7
The :class:`.GenericMemachedBackend` uses a ``threading.local()``
object to store individual client objects per thread,
as most modern memcached clients do not appear to be inherently
threadsafe.
In particular, ``threading.local()`` has the advantage over pylibmc's
built-in thread pool in that it automatically discards objects
associated with a particular thread when that thread ends.
"""
set_arguments: Mapping[str, Any] = {}
"""Additional arguments which will be passed
to the :meth:`set` method."""
# No need to override serializer, as all the memcached libraries
# handles that themselves. Still, we support customizing the
# serializer/deserializer to use better default pickle protocol
# or completely different serialization mechanism
serializer = None
deserializer = None
def __init__(self, arguments):
self._imports()
# using a plain threading.local here. threading.local
# automatically deletes the __dict__ when a thread ends,
# so the idea is that this is superior to pylibmc's
# own ThreadMappedPool which doesn't handle this
# automatically.
self.url = util.to_list(arguments["url"])
self.distributed_lock = arguments.get("distributed_lock", False)
self.lock_timeout = arguments.get("lock_timeout", 0)
def has_lock_timeout(self):
return self.lock_timeout != 0
def _imports(self):
"""client library imports go here."""
raise NotImplementedError()
def _create_client(self):
"""Creation of a Client instance goes here."""
raise NotImplementedError()
@util.memoized_property
def _clients(self):
backend = self
class ClientPool(threading.local):
def __init__(self):
self.memcached = backend._create_client()
return ClientPool()
@property
def client(self):
"""Return the memcached client.
This uses a threading.local by
default as it appears most modern
memcached libs aren't inherently
threadsafe.
"""
return self._clients.memcached
def get_mutex(self, key):
if self.distributed_lock:
return MemcachedLock(
lambda: self.client, key, timeout=self.lock_timeout
)
else:
return None
def get(self, key):
value = self.client.get(key)
if value is None:
return NO_VALUE
else:
return value
def get_multi(self, keys):
values = self.client.get_multi(keys)
return [
NO_VALUE if val is None else val
for val in [values.get(key, NO_VALUE) for key in keys]
]
def set(self, key, value):
self.client.set(key, value, **self.set_arguments)
def set_multi(self, mapping):
mapping = {key: value for key, value in mapping.items()}
self.client.set_multi(mapping, **self.set_arguments)
def delete(self, key):
self.client.delete(key)
def delete_multi(self, keys):
self.client.delete_multi(keys)
class MemcacheArgs(GenericMemcachedBackend):
"""Mixin which provides support for the 'time' argument to set(),
'min_compress_len' to other methods.
:param memcached_expire_time: integer, when present will
be passed as the ``time`` parameter to the ``set`` method.
This is used to set the memcached expiry time for a value.
.. note::
This parameter is **different** from Dogpile's own
``expiration_time``, which is the number of seconds after
which Dogpile will consider the value to be expired.
When Dogpile considers a value to be expired,
it **continues to use the value** until generation
of a new value is complete, when using
:meth:`.CacheRegion.get_or_create`.
Therefore, if you are setting ``memcached_expire_time``, you'll
want to make sure it is greater than ``expiration_time``
by at least enough seconds for new values to be generated,
else the value won't be available during a regeneration,
forcing all threads to wait for a regeneration each time
a value expires.
:param min_compress_len: Threshold length to kick in auto-compression
of the value using the compressor
"""
def __init__(self, arguments):
self.min_compress_len = arguments.get("min_compress_len", 0)
self.set_arguments = {}
if "memcached_expire_time" in arguments:
self.set_arguments["time"] = arguments["memcached_expire_time"]
if "min_compress_len" in arguments:
self.set_arguments["min_compress_len"] = arguments[
"min_compress_len"
]
super(MemcacheArgs, self).__init__(arguments)
class PylibmcBackend(MemcacheArgs, GenericMemcachedBackend):
"""A backend for the
`pylibmc <http://sendapatch.se/projects/pylibmc/index.html>`_
memcached client.
A configuration illustrating several of the optional
arguments described in the pylibmc documentation::
from dogpile.cache import make_region
region = make_region().configure(
'dogpile.cache.pylibmc',
expiration_time = 3600,
arguments = {
'url':["127.0.0.1"],
'binary':True,
'behaviors':{"tcp_nodelay": True,"ketama":True}
}
)
Arguments accepted here include those of
:class:`.GenericMemcachedBackend`, as well as
those below.
:param binary: sets the ``binary`` flag understood by
``pylibmc.Client``.
:param behaviors: a dictionary which will be passed to
``pylibmc.Client`` as the ``behaviors`` parameter.
:param min_compress_len: Integer, will be passed as the
``min_compress_len`` parameter to the ``pylibmc.Client.set``
method.
"""
def __init__(self, arguments):
self.binary = arguments.get("binary", False)
self.behaviors = arguments.get("behaviors", {})
super(PylibmcBackend, self).__init__(arguments)
def _imports(self):
global pylibmc
import pylibmc # noqa
def _create_client(self):
return pylibmc.Client(
self.url, binary=self.binary, behaviors=self.behaviors
)
class MemcachedBackend(MemcacheArgs, GenericMemcachedBackend):
"""A backend using the standard
`Python-memcached <http://www.tummy.com/Community/software/\
python-memcached/>`_
library.
Example::
from dogpile.cache import make_region
region = make_region().configure(
'dogpile.cache.memcached',
expiration_time = 3600,
arguments = {
'url':"127.0.0.1:11211"
}
)
:param dead_retry: Number of seconds memcached server is considered dead
before it is tried again. Will be passed to ``memcache.Client``
as the ``dead_retry`` parameter.
.. versionchanged:: 1.1.8 Moved the ``dead_retry`` argument which was
erroneously added to "set_parameters" to
be part of the Memcached connection arguments.
:param socket_timeout: Timeout in seconds for every call to a server.
Will be passed to ``memcache.Client`` as the ``socket_timeout``
parameter.
.. versionchanged:: 1.1.8 Moved the ``socket_timeout`` argument which
was erroneously added to "set_parameters"
to be part of the Memcached connection arguments.
"""
def __init__(self, arguments):
self.dead_retry = arguments.get("dead_retry", 30)
self.socket_timeout = arguments.get("socket_timeout", 3)
super(MemcachedBackend, self).__init__(arguments)
def _imports(self):
global memcache
import memcache # noqa
def _create_client(self):
return memcache.Client(
self.url,
dead_retry=self.dead_retry,
socket_timeout=self.socket_timeout,
)
class BMemcachedBackend(GenericMemcachedBackend):
"""A backend for the
`python-binary-memcached <https://github.com/jaysonsantos/\
python-binary-memcached>`_
memcached client.
This is a pure Python memcached client which includes
security features like SASL and SSL/TLS.
SASL is a standard for adding authentication mechanisms
to protocols in a way that is protocol independent.
A typical configuration using username/password::
from dogpile.cache import make_region
region = make_region().configure(
'dogpile.cache.bmemcached',
expiration_time = 3600,
arguments = {
'url':["127.0.0.1"],
'username':'scott',
'password':'tiger'
}
)
A typical configuration using tls_context::
import ssl
from dogpile.cache import make_region
ctx = ssl.create_default_context(cafile="/path/to/my-ca.pem")
region = make_region().configure(
'dogpile.cache.bmemcached',
expiration_time = 3600,
arguments = {
'url':["127.0.0.1"],
'tls_context':ctx,
}
)
For advanced ways to configure TLS creating a more complex
tls_context visit https://docs.python.org/3/library/ssl.html
Arguments which can be passed to the ``arguments``
dictionary include:
:param username: optional username, will be used for
SASL authentication.
:param password: optional password, will be used for
SASL authentication.
:param tls_context: optional TLS context, will be used for
TLS connections.
.. versionadded:: 1.0.2
"""
def __init__(self, arguments):
self.username = arguments.get("username", None)
self.password = arguments.get("password", None)
self.tls_context = arguments.get("tls_context", None)
super(BMemcachedBackend, self).__init__(arguments)
def _imports(self):
global bmemcached
import bmemcached
def _create_client(self):
return bmemcached.Client(
self.url,
username=self.username,
password=self.password,
tls_context=self.tls_context,
)
def delete_multi(self, keys):
"""python-binary-memcached api does not implements delete_multi"""
for key in keys:
self.delete(key)
class PyMemcacheBackend(GenericMemcachedBackend):
"""A backend for the
`pymemcache <https://github.com/pinterest/pymemcache>`_
memcached client.
A comprehensive, fast, pure Python memcached client
.. versionadded:: 1.1.2
pymemcache supports the following features:
* Complete implementation of the memcached text protocol.
* Configurable timeouts for socket connect and send/recv calls.
* Access to the "noreply" flag, which can significantly increase
the speed of writes.
* Flexible, simple approach to serialization and deserialization.
* The (optional) ability to treat network and memcached errors as
cache misses.
dogpile.cache uses the ``HashClient`` from pymemcache in order to reduce
API differences when compared to other memcached client drivers.
This allows the user to provide a single server or a list of memcached
servers.
Arguments which can be passed to the ``arguments``
dictionary include:
:param tls_context: optional TLS context, will be used for
TLS connections.
A typical configuration using tls_context::
import ssl
from dogpile.cache import make_region
ctx = ssl.create_default_context(cafile="/path/to/my-ca.pem")
region = make_region().configure(
'dogpile.cache.pymemcache',
expiration_time = 3600,
arguments = {
'url':["127.0.0.1"],
'tls_context':ctx,
}
)
.. seealso::
`<https://docs.python.org/3/library/ssl.html>`_ - additional TLS
documentation.
:param serde: optional "serde". Defaults to
``pymemcache.serde.pickle_serde``.
:param default_noreply: defaults to False. When set to True this flag
enables the pymemcache "noreply" feature. See the pymemcache
documentation for further details.
:param socket_keepalive: optional socket keepalive, will be used for
TCP keepalive configuration. Use of this parameter requires pymemcache
3.5.0 or greater. This parameter
accepts a
`pymemcache.client.base.KeepAliveOpts
<https://pymemcache.readthedocs.io/en/latest/apidoc/pymemcache.client.base.html#pymemcache.client.base.KeepaliveOpts>`_
object.
A typical configuration using ``socket_keepalive``::
from pymemcache import KeepaliveOpts
from dogpile.cache import make_region
# Using the default keepalive configuration
socket_keepalive = KeepaliveOpts()
region = make_region().configure(
'dogpile.cache.pymemcache',
expiration_time = 3600,
arguments = {
'url':["127.0.0.1"],
'socket_keepalive': socket_keepalive
}
)
.. versionadded:: 1.1.4 - added support for ``socket_keepalive``.
:param enable_retry_client: optional flag to enable retry client
mechanisms to handle failure. Defaults to False. When set to ``True``,
the :paramref:`.PyMemcacheBackend.retry_attempts` parameter must also
be set, along with optional parameters
:paramref:`.PyMemcacheBackend.retry_delay`.
:paramref:`.PyMemcacheBackend.retry_for`,
:paramref:`.PyMemcacheBackend.do_not_retry_for`.
.. seealso::
`<https://pymemcache.readthedocs.io/en/latest/getting_started.html#using-the-built-in-retrying-mechanism>`_ -
in the pymemcache documentation
.. versionadded:: 1.1.4
:param retry_attempts: how many times to attempt an action with
pymemcache's retrying wrapper before failing. Must be 1 or above.
Defaults to None.
.. versionadded:: 1.1.4
:param retry_delay: optional int|float, how many seconds to sleep between
each attempt. Used by the retry wrapper. Defaults to None.
.. versionadded:: 1.1.4
:param retry_for: optional None|tuple|set|list, what exceptions to
allow retries for. Will allow retries for all exceptions if None.
Example: ``(MemcacheClientError, MemcacheUnexpectedCloseError)``
Accepts any class that is a subclass of Exception. Defaults to None.
.. versionadded:: 1.1.4
:param do_not_retry_for: optional None|tuple|set|list, what
exceptions should be retried. Will not block retries for any Exception if
None. Example: ``(IOError, MemcacheIllegalInputError)``
Accepts any class that is a subclass of Exception. Defaults to None.
.. versionadded:: 1.1.4
:param hashclient_retry_attempts: Amount of times a client should be tried
before it is marked dead and removed from the pool in the HashClient's
internal mechanisms.
.. versionadded:: 1.1.5
:param hashclient_retry_timeout: Time in seconds that should pass between
retry attempts in the HashClient's internal mechanisms.
.. versionadded:: 1.1.5
:param dead_timeout: Time in seconds before attempting to add a node
back in the pool in the HashClient's internal mechanisms.
.. versionadded:: 1.1.5
:param memcached_expire_time: integer, when present will
be passed as the ``time`` parameter to the ``set`` method.
This is used to set the memcached expiry time for a value.
.. note::
This parameter is **different** from Dogpile's own
``expiration_time``, which is the number of seconds after
which Dogpile will consider the value to be expired.
When Dogpile considers a value to be expired,
it **continues to use the value** until generation
of a new value is complete, when using
:meth:`.CacheRegion.get_or_create`.
Therefore, if you are setting ``memcached_expire_time``, you'll
want to make sure it is greater than ``expiration_time``
by at least enough seconds for new values to be generated,
else the value won't be available during a regeneration,
forcing all threads to wait for a regeneration each time
a value expires.
.. versionadded:: 1.3.3
""" # noqa E501
def __init__(self, arguments):
super().__init__(arguments)
self.serde = arguments.get("serde", pymemcache.serde.pickle_serde)
self.default_noreply = arguments.get("default_noreply", False)
self.tls_context = arguments.get("tls_context", None)
self.socket_keepalive = arguments.get("socket_keepalive", None)
self.enable_retry_client = arguments.get("enable_retry_client", False)
self.retry_attempts = arguments.get("retry_attempts", None)
self.retry_delay = arguments.get("retry_delay", None)
self.retry_for = arguments.get("retry_for", None)
self.do_not_retry_for = arguments.get("do_not_retry_for", None)
self.hashclient_retry_attempts = arguments.get(
"hashclient_retry_attempts", 2
)
self.hashclient_retry_timeout = arguments.get(
"hashclient_retry_timeout", 1
)
self.dead_timeout = arguments.get("hashclient_dead_timeout", 60)
if (
self.retry_delay is not None
or self.retry_attempts is not None
or self.retry_for is not None
or self.do_not_retry_for is not None
) and not self.enable_retry_client:
warnings.warn(
"enable_retry_client is not set; retry options "
"will be ignored"
)
self.set_arguments = {}
if "memcached_expire_time" in arguments:
self.set_arguments["expire"] = arguments["memcached_expire_time"]
def _imports(self):
global pymemcache
import pymemcache
def _create_client(self):
_kwargs = {
"serde": self.serde,
"default_noreply": self.default_noreply,
"tls_context": self.tls_context,
"retry_attempts": self.hashclient_retry_attempts,
"retry_timeout": self.hashclient_retry_timeout,
"dead_timeout": self.dead_timeout,
}
if self.socket_keepalive is not None:
_kwargs.update({"socket_keepalive": self.socket_keepalive})
client = pymemcache.client.hash.HashClient(self.url, **_kwargs)
if self.enable_retry_client:
return pymemcache.client.retrying.RetryingClient(
client,
attempts=self.retry_attempts,
retry_delay=self.retry_delay,
retry_for=self.retry_for,
do_not_retry_for=self.do_not_retry_for,
)
return client
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