'use strict';
+
+function Queue(options) {
+ if (!(this instanceof Queue)) {
+ return new Queue(options);
+ }
+
+ options = options || {};
+ this.concurrency = options.concurrency || Infinity;
+ this.pending = 0;
+ this.jobs = [];
+ this.cbs = [];
+ this._done = done.bind(this);
+}
+
+var arrayAddMethods = [
+ 'push',
+ 'unshift',
+ 'splice'
+];
+
+arrayAddMethods.forEach(function(method) {
+ Queue.prototype[method] = function() {
+ var methodResult = Array.prototype[method].apply(this.jobs, arguments);
+ this._run();
+ return methodResult;
+ };
+});
+
+Object.defineProperty(Queue.prototype, 'length', {
+ get: function() {
+ return this.pending + this.jobs.length;
+ }
+});
+
+Queue.prototype._run = function() {
+ if (this.pending === this.concurrency) {
+ return;
+ }
+ if (this.jobs.length) {
+ var job = this.jobs.shift();
+ this.pending++;
+ job(this._done);
+ this._run();
+ }
+
+ if (this.pending === 0) {
+ while (this.cbs.length !== 0) {
+ var cb = this.cbs.pop();
+ process.nextTick(cb);
+ }
+ }
+};
+
+Queue.prototype.onDone = function(cb) {
+ Eif (typeof cb === 'function') {
+ this.cbs.push(cb);
+ this._run();
+ }
+};
+
+function done() {
+ this.pending--;
+ this._run();
+}
+
+module.exports = Queue;
+ |