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