91 lines
2.7 KiB
JavaScript
91 lines
2.7 KiB
JavaScript
// MAP DATA CACHE ///////////////////////////////////
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// cache for map data tiles.
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window.DataCache = function() {
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this.REQUEST_CACHE_FRESH_AGE = 3*60; // if younger than this, use data in the cache rather than fetching from the server
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this.REQUEST_CACHE_MAX_AGE = 15*60; // maximum cache age. entries are deleted from the cache after this time
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if (L.Browser.mobile) {
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// on mobile devices, smaller cache size
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this.REQUEST_CACHE_MAX_SIZE = 300; // if more than this many entries, expire early
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} else {
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// but on desktop, allow more
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this.REQUEST_CACHE_MAX_SIZE = 1000; // if more than this many entries, expire early
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}
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this._cache = {};
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this._interval = undefined;
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}
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window.DataCache.prototype.store = function(qk,data,freshTime) {
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// fixme? common behaviour for objects is that properties are kept in the order they're added
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// this is handy, as it allows easy retrieval of the oldest entries for expiring
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// however, this is not guaranteed by the standards, but all our supported browsers work this way
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delete this._cache[qk];
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var time = new Date().getTime();
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if (freshTime===undefined) freshTime = this.REQUEST_CACHE_FRESH_AGE*1000;
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var expire = time + freshTime;
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this._cache[qk] = { time: time, expire: expire, data: data };
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}
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window.DataCache.prototype.get = function(qk) {
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if (qk in this._cache) return this._cache[qk].data;
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else return undefined;
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}
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window.DataCache.prototype.getTime = function(qk) {
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if (qk in this._cache) return this._cache[qk].time;
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else return 0;
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}
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window.DataCache.prototype.isFresh = function(qk) {
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if (qk in this._cache) {
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var d = new Date();
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var t = d.getTime();
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if (this._cache[qk].expire >= t) return true;
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else return false;
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}
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return undefined;
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}
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window.DataCache.prototype.startExpireInterval = function(period) {
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if (this._interval === undefined) {
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var savedContext = this;
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this._interval = setInterval (function() { savedContext.runExpire(); }, period*1000);
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}
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}
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window.DataCache.prototype.stopExpireInterval = function() {
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if (this._interval !== undefined) {
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stopInterval (this._interval);
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this._interval = undefined;
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}
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}
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window.DataCache.prototype.runExpire = function() {
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var d = new Date();
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var t = d.getTime()-this.REQUEST_CACHE_MAX_AGE*1000;
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var cacheSize = Object.keys(this._cache).length;
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for(var qk in this._cache) {
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// fixme? our MAX_SIZE test here assumes we're processing the oldest first. this relies
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// on looping over object properties in the order they were added. this is true in most browsers,
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// but is not a requirement of the standards
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if (cacheSize > this.REQUEST_CACHE_MAX_SIZE || this._cache[qk].time < t) {
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delete this._cache[qk];
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cacheSize--;
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}
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}
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}
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