javascript 多线程异步队列

/*!
 * 多线程异步队列
 * 依赖 jQuery 1.8+ (如果你用的是 1.6或1.7, 只要将源码中的 then方法替换为pipe方法 即可)
 */

/**
 * @n {Number} 正整数, 线程数量
 */
function Queue (n) {
    n = parseInt(n || 1, 10);
    return (n && n > 0) ? new Queue.prototype.init(n) : null;
}

Queue.prototype = {
    init: function (n) {
        this.threads = [];
        this.taskList = [];

        while (n--) {
            this.threads.push(new this.Thread)
        }
    },

    /**
     * @callback {Fucntion} promise对象done时的回调函数，它的返回值必须是一个promise对象
     */
    push: function (callback) {
        if (typeof callback !== ‘function‘) return;

        var index = this.indexOfIdle();

        if (index != -1) {
            this.threads[index].idle(callback)
            try { console.log(‘Thread-‘ + (index+1) + ‘ accept the task!‘) } catch (e) {}
        }
        else {
            this.taskList.push(callback);

            for (var i = 0, l = this.threads.length; i < l; i++) {

                (function(thread, self, id){
                    thread.idle(function(){
                        if (self.taskList.length > 0) {
                            try { console.log(‘Thread-‘ + (id+1) + ‘ accept the task!‘) } catch (e) {}

                            var promise = self.taskList.pop()();    // 正确的返回值应该是一个promise对象
                            return promise.promise ? promise : thread.promise;
                        } else {
                            return thread.promise
                        }
                    })
                })(this.threads[i], this, i);

            }
        }
    },
    indexOfIdle: function () {
        var threads = this.threads,
            thread = null,
            index = -1;

        for (var i = 0, l = threads.length; i < l; i++) {
            thread = threads[i];

            if (thread.promise.state() === ‘resolved‘) {
                index = i;
                break;
            }
        }

        return index;
    },
    Thread: function () {
        this.promise = $.Deferred().resolve().promise();

        this.idle = function (callback) {
            this.promise = this.promise.then(callback)
        }
    }
};

Queue.prototype.init.prototype = Queue.prototype;

    var queue = new Queue(3);    // 创建一个具有3个线程的队列

　　// task-1
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 8000);

        return defer.promise()
    })

　　// task-2
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 2000);

        return defer.promise()
    })

　　// task-3
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 6000);

        return defer.promise()
    })

　　// task-4
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 3000);

        return defer.promise()
    })

　　// task-5
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 2000);

        return defer.promise()
    })

　　// task-6
    queue.push(function(){
        var defer = $.Deferred();

        setTimeout(function(){
            defer.resolve()
        }, 2000);

        return defer.promise()
    })