dogpile.cache
=============

A caching API built around the concept of a "dogpile lock", which allows
continued access to an expiring data value while a single thread generates a
new value.

dogpile.cache builds on the `dogpile.core <http://pypi.python.org/pypi/dogpile.core>`_
locking system, which implements the idea of "allow one creator to write while
others read" in the abstract.   Overall, dogpile.cache is intended as a
replacement to the `Beaker <http://beaker.groovie.org>`_ caching system, the internals
of which are written by the same author.   All the ideas of Beaker which "work"
are re-implemented in dogpile.cache in a more efficient and succinct manner,
and all the cruft (Beaker's internals were first written in 2005) relegated
to the trash heap.

Features
--------

* A succinct API which encourages up-front configuration of pre-defined
  "regions", each one defining a set of caching characteristics including
  storage backend, configuration options, and default expiration time.
* A standard get/set/delete API as well as a function decorator API is
  provided.
* The mechanics of key generation are fully customizable.   The function
  decorator API features a pluggable "key generator" to customize how
  cache keys are made to correspond to function calls, and an optional
  "key mangler" feature provides for pluggable mangling of keys
  (such as encoding, SHA-1 hashing) as desired for each region.
* The dogpile lock, first developed as the core engine behind the Beaker
  caching system, here vastly simplified, improved, and better tested.
  Some key performance
  issues that were intrinsic to Beaker's architecture, particularly that
  values would frequently be "double-fetched" from the cache, have been fixed.
* Backends implement their own version of a "distributed" lock, where the
  "distribution" matches the backend's storage system.  For example, the
  memcached backends allow all clients to coordinate creation of values
  using memcached itself.   The dbm file backend uses a lockfile
  alongside the dbm file.  New backends, such as a Redis-based backend,
  can provide their own locking mechanism appropriate to the storage
  engine.
* Writing new backends or hacking on the existing backends is intended to be
  routine - all that's needed are basic get/set/delete methods. A distributed
  lock tailored towards the backend is an optional addition, else dogpile uses
  a regular thread mutex. New backends can be registered with dogpile.cache
  directly or made available via setuptools entry points.
* Included backends feature three memcached backends (python-memcached, pylibmc,
  bmemcached), a Redis backend, a backend based on Python's
  anydbm, and a plain dictionary backend.
* Space for third party plugins, including the first which provides the
  dogpile.cache engine to Mako templates.
* Python 3 compatible in place - no 2to3 required.

Synopsis
--------

dogpile.cache features a single public usage object known as the ``CacheRegion``.
This object then refers to a particular ``CacheBackend``.   Typical usage
generates a region using ``make_region()``, which can then be used at the
module level to decorate functions, or used directly in code with a traditional
get/set interface.   Configuration of the backend is applied to the region
using ``configure()`` or ``configure_from_config()``, allowing deferred
config-file based configuration to occur after modules have been imported::

    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}
        }
    )

    @region.cache_on_arguments()
    def load_user_info(user_id):
        return some_database.lookup_user_by_id(user_id)


Documentation
-------------

See dogpile.cache's full documentation at
`dogpile.cache documentation <http://dogpilecache.readthedocs.org>`_.