115 lines
3.1 KiB
JavaScript
115 lines
3.1 KiB
JavaScript
/** @license MIT License (c) copyright 2012-2013 original author or authors */
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/**
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* poll.js
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*
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* Helper that polls until cancelled or for a condition to become true.
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*
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* @author Scott Andrews
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*/
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(function (define) { 'use strict';
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define(function(require) {
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var when = require('./when');
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var attempt = when['try'];
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var cancelable = require('./cancelable');
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/**
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* Periodically execute the task function on the msec delay. The result of
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* the task may be verified by watching for a condition to become true. The
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* returned deferred is cancellable if the polling needs to be cancelled
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* externally before reaching a resolved state.
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*
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* The next vote is scheduled after the results of the current vote are
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* verified and rejected.
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*
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* Polling may be terminated by the verifier returning a truthy value,
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* invoking cancel() on the returned promise, or the task function returning
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* a rejected promise.
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*
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* Usage:
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*
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* var count = 0;
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* function doSomething() { return count++ }
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*
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* // poll until cancelled
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* var p = poll(doSomething, 1000);
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* ...
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* p.cancel();
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*
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* // poll until condition is met
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* poll(doSomething, 1000, function(result) { return result > 10 })
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* .then(function(result) { assert result == 10 });
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*
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* // delay first vote
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* poll(doSomething, 1000, anyFunc, true);
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*
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* @param task {Function} function that is executed after every timeout
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* @param interval {number|Function} timeout in milliseconds
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* @param [verifier] {Function} function to evaluate the result of the vote.
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* May return a {Promise} or a {Boolean}. Rejecting the promise or a
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* falsey value will schedule the next vote.
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* @param [delayInitialTask] {boolean} if truthy, the first vote is scheduled
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* instead of immediate
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*
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* @returns {Promise}
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*/
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return function poll(task, interval, verifier, delayInitialTask) {
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var deferred, canceled, reject;
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canceled = false;
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deferred = cancelable(when.defer(), function () { canceled = true; });
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reject = deferred.reject;
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verifier = verifier || function () { return false; };
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if (typeof interval !== 'function') {
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interval = (function (interval) {
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return function () { return when().delay(interval); };
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})(interval);
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}
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function certify(result) {
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deferred.resolve(result);
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}
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function schedule(result) {
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attempt(interval).then(vote, reject);
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if (result !== void 0) {
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deferred.notify(result);
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}
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}
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function vote() {
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if (canceled) { return; }
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when(task(),
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function (result) {
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when(verifier(result),
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function (verification) {
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return verification ? certify(result) : schedule(result);
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},
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function () { schedule(result); }
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);
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},
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reject
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);
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}
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if (delayInitialTask) {
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schedule();
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} else {
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// if task() is blocking, vote will also block
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vote();
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}
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// make the promise cancelable
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deferred.promise = Object.create(deferred.promise);
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deferred.promise.cancel = deferred.cancel;
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return deferred.promise;
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};
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});
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})(typeof define === 'function' && define.amd ? define : function (factory) { module.exports = factory(require); });
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