Products.StandardCacheManagers 3.0

Overview

This package provides two cache managers for Zope 2. A RAMCacheManager and an Accelerated HTTP cache manager, which adds HTTP cache headers to responses.

The following is intended for people interested in the internals of RAMCacheManager, such as maintainers.

Introduction

The caching framework does not interpret the data in any way, it acts just as a general storage for data passed to it. It tries to check if the data is pickleable though. IOW, only pickleable data is cacheable.

The idea behind the RAMCacheManager is that it should be shared between threads, so that the same objects are not cached in each thread. This is achieved by storing the cache data structure itself as a module level variable (RAMCacheManager.caches). This, of course, requires locking on modifications of that data structure.

Each RAMCacheManager instance has one cache in RAMCacheManager.caches dictionary. A unique __cacheid is generated when creating a cache manager and it’s used as a key for caches.

Object Hierarchy

RAMCacheManager

RAMCache

ObjectCacheEntries

CacheEntry

RAMCacheManager is a persistent placeful object. It is assigned a unique __cacheid on its creation. It is then used as a key to look up the corresponding RAMCache object in the global caches dictionary. So, each RAMCacheManager has a single RAMCache related to it.

RAMCache is a volatile cache, unique for each RAMCacheManager. It is shared among threads and does all the locking. It has a writelock. No locking is done on reading though. RAMCache keeps a dictionary of ObjectCacheEntries indexed by the physical path of a cached object.

ObjectCacheEntries is a container for cached values for a single object. The values in it are indexed by a tuple of a view_name, interesting request variables, and extra keywords passed to Cache.ZCache_set().

CacheEntry is a wrapper around a single cached value. It stores the data itself, creation time, view_name and keeps the access count.

Changelog