75a0cbe43d
Add a decorator to handle the caching of objects stored to and/or read from persistence (bring over from pre-Angular branch.) Supports the WARP Telemetry Adapter; the absence of such a cache has been observed to result in significant latency in instantiating autoflow tabular views for packets. WTD-644. Also, include an empty test file to ensure that the added decorator is included in code coverage estimation (and to provide a location for tests to be written later.)
100 lines
3.9 KiB
JavaScript
100 lines
3.9 KiB
JavaScript
/*global define*/
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define(
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[],
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function () {
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'use strict';
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/**
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* A caching persistence decorator maintains local copies of persistent objects
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* that have been loaded, and keeps them in sync after writes. This allows
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* retrievals to occur more quickly after the first load.
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*
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* @constructor
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* @param {string[]} CACHE_SPACES persistence space names which
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* should be cached
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* @param {PersistenceService} persistenceService the service which
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* implements object persistence, whose inputs/outputs
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* should be cached.
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*/
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function CachingPersistenceDecorator(CACHE_SPACES, persistenceService) {
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var spaces = CACHE_SPACES || [], // List of spaces to cache
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cache = {}; // Where objects will be stored
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// Utility function; avoid sharing one instance everywhere.
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function clone(value) {
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// Only clone truthy values (no need to clone undefined, false...)
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return value && JSON.parse(JSON.stringify(value));
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}
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// Place value in the cache for space, if there is one.
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function addToCache(space, key, value) {
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if (cache[space]) {
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cache[space][key] = { value: clone(value) };
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}
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}
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// Create a function for putting value into a cache;
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// useful for then-chaining.
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function putCache(space, key) {
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return function (value) {
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addToCache(space, key, value);
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return value;
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};
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}
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// Wrap as a thenable; used instead of $q.when because that
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// will resolve on a future tick, which can cause latency
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// issues (which this decorator is intended to address.)
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function fastPromise(value) {
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return {
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then: function (callback) {
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return fastPromise(callback(value));
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}
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};
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}
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// Arrayify list of spaces to cache, if necessary.
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spaces = Array.isArray(spaces) ? spaces : [ spaces ];
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// Initialize caches
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spaces.forEach(function (space) {
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cache[space] = {};
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});
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// Provide PersistenceService interface; mostly delegate to the
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// decorated service, intervene and cache where appropriate.
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return {
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listSpaces: function () {
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return persistenceService.listSpaces();
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},
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listObjects: function (space) {
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return persistenceService.listObjects(space);
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},
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createObject: function (space, key, value) {
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addToCache(space, key, value);
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return persistenceService.createObject(space, key, value);
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},
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readObject: function (space, key) {
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return (cache[space] && cache[space][key]) ?
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fastPromise(clone(cache[space][key].value)) :
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persistenceService.readObject(space, key)
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.then(putCache(space, key));
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},
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updateObject: function (space, key, value) {
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addToCache(space, key, value);
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return persistenceService.updateObject(space, key, value);
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},
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deleteObject: function (space, key, value) {
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if (cache[space]) {
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delete cache[space][key];
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}
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return persistenceService.deleteObject(space, key, value);
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}
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};
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}
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return CachingPersistenceDecorator;
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}
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); |