filecache

A simple file cache of pure Golang

Install

First, you need to install the package:

go get -u github.com/ucwong/filecache

Overview

A file cache can be created with either the NewDefaultCache() function to get a cache with the defaults set, or NewCache() to get a new cache with 0 values for everything; you will not be able to store items in this cache until the values are changed; specifically, at a minimum, you should set the MaxItems field to be > 0.

Let's start with a basic example; we'll create a basic cache and give it a maximum item size of 128M:

import (
      "github.com/ucwong/filecache"
)

...

cache := filecache.NewDefaultCache()
cache.MaxSize = 128 * filecache.Megabyte
cache.Start()

...

cache.Stop()

The Kilobyte, Megabyte, and Gigabyte constants are provided as a convience when setting cache sizes.

When cache.Start() is called, a goroutine is launched in the background that routinely checks the cache for expired items. The delay between runs is specified as the number of seconds given by cache.Every ("every cache.Every seconds, check for expired items"). There are three criteria used to determine whether an item in the cache should be expired; they are:

1. Has the file been modified on disk? (The cache stores the last time of modification at the time of caching, and compares that to the file's current last modification time).
2. Has the file been in the cache for longer than the maximum allowed time?
3. Is the cache at capacity? When a file is being cached, a check is made to see if the cache is currently filled. If it is, the item that was last accessed the longest ago is expired and the new item takes its place. When loading items asynchronously, this check might miss the fact that the cache will be at capacity; the background scanner performs a check after its regular checks to ensure that the cache is not at capacity.

The background scanner can be disabled by setting cache.Every to 0; if so, cache expiration is only done when the cache is at capacity.

Once the cache is no longer needed, a call to cache.Stop() will close down the channels and signal the background scanner that it should stop.