72 lines
1.9 KiB
JavaScript
72 lines
1.9 KiB
JavaScript
/** @license MIT License (c) copyright 2011-2013 original author or authors */
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/**
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* Generalized promise concurrency guard
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* Adapted from original concept by Sakari Jokinen (Rocket Pack, Ltd.)
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*
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* @author Brian Cavalier
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* @author John Hann
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* @contributor Sakari Jokinen
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*/
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(function(define) {
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define(function(require) {
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var when = require('./when');
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var slice = Array.prototype.slice;
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guard.n = n;
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return guard;
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/**
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* Creates a guarded version of f that can only be entered when the supplied
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* condition allows.
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* @param {function} condition represents a critical section that may only
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* be entered when allowed by the condition
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* @param {function} f function to guard
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* @returns {function} guarded version of f
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*/
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function guard(condition, f) {
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return function() {
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var args = slice.call(arguments);
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return when(condition()).withThis(this).then(function(exit) {
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return when(f.apply(this, args))['finally'](exit);
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});
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};
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}
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/**
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* Creates a condition that allows only n simultaneous executions
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* of a guarded function
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* @param {number} allowed number of allowed simultaneous executions
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* @returns {function} condition function which returns a promise that
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* fulfills when the critical section may be entered. The fulfillment
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* value is a function ("notifyExit") that must be called when the critical
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* section has been exited.
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*/
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function n(allowed) {
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var count = 0;
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var waiting = [];
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return function enter() {
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return when.promise(function(resolve) {
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if(count < allowed) {
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resolve(exit);
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} else {
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waiting.push(resolve);
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}
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count += 1;
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});
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};
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function exit() {
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count = Math.max(count - 1, 0);
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if(waiting.length > 0) {
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waiting.shift()(exit);
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}
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}
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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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