/
cache.js
112 lines (98 loc) · 2.35 KB
/
cache.js
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var extend = require('lodash.assign')
, EventEmitter = require('events').EventEmitter
module.exports = function(opts) {
var cache
, lru
, lruId = 0
, gcHandle
, instance = new EventEmitter()
, options = extend(
{ gcInterval: 30000 // How often GC happens
, maxLength: 1000 // Maximum number of items that can be held in the cache by default.
, lruWriteCleanUp: 100 // Run the LRU clean up every 'lruWriteCleanUp' writes
}, opts)
function clear() {
cache = {}
lru = {}
}
function del(key) {
var item = cache[key]
if (item) {
delete lru[item.lru];
delete cache[key]
}
}
function garbageCollection() {
Object.keys(cache).forEach(function(key) {
var item = cache[key]
if (item.expire <= Date.now()) {
expire(key, item)
}
})
lruClean()
}
function lruClean() {
var overage = Object.keys(cache).length - options.maxLength
, cacheId
, lruKeys = Object.keys(lru)
, lruKey
for (var i = 0; i < overage; i++) {
lruKey = lruKeys.shift()
cacheId = lru[lruKey];
delete lru[lruKey];
delete cache[cacheId]
}
}
function expire(key, item) {
del(key)
instance.emit('expired', key, item.value)
}
clear()
gcHandle = setInterval(garbageCollection, options.gcInterval)
extend(instance, {
set: function(key, value, ttl) {
if (typeof key === 'undefined') {
throw new Error('Invalid key undefined')
}
var item = { value: value, lru: lruId }
if (ttl) {
item.expire = Date.now() + ttl
}
cache[key] = item
lru[lruId] = key
lruId++
if (lruId % options.lruWriteCleanUp === 0) {
lruClean()
}
},
get: function(key) {
var response
, item = cache[key]
if (item) {
if ((item.expire) && (item.expire < Date.now())) {
expire(key, item)
return undefined
}
response = item.value;
lru[lruId] = key
item.lru = lruId
lruId++
}
return response
},
del: del,
clear: clear,
gc: lruClean,
size: function() {
garbageCollection()
return Object.keys(cache).length
},
dump: function() {
return cache
},
close: function() {
clearInterval(gcHandle)
}
})
return instance
}