PromisePool.v2.js

//{{ PromisePool
/* Usage:
 var promise_pool = new PromisePool([concurrency_limit]);
    * concurrency_limit: n of concurrency promices executions
    generate a PromisePool

 promise_pool.push(fn);
    * function: the function to generate promise object
    push a function into PromisePool, this functipn will generate promise object
    but the real Promise object has *NOT* been generated yet
 
 promise_pool.start();
    generate and execute all Promises in pool base on the concurrency_limit
    return a Promise object resolved when all Promises object in pool are resolved/rejected

 */

var PromisePool = function(limit) {
    this.queue = [];
    this.limit = (limit > 0) ? limit: 10;
};
PromisePool.prototype = {
    constructor: PromisePool,
    push: function(fn){
        this.queue.push(fn);
    },
    start: function(){
        var that = this;
        var p = Promise.resolve();
        var results = [];
        var process = function(group){
            return Promise.all(group.map(function(fn){
                return fn();
            })).then(function(r){
                results.push.apply(results, r);
                console.log(results.length, 'results merge done');
                return results;
            });
        };
        while(that.queue.length) {
            p = p.then(
                process.bind(that, that.queue.splice(0, that.limit))
            );
        }
        return p;
    }
};
////}}
//{{ Scenario 1
    // Old Scheme
    var promise_list = [];
    promise_list.push(new Promise(function(resolve, reject){
        // promise 1 
    }));
    promise_list.push(new Promise(function(resolve, reject){
        // promise 2 
    }));
    promise_list.push(new Promise(function(resolve, reject){
        // promise 3 
    }));
    Promise.all(promise_list).then(function(results){
        console.log('all done');
    });


    // New Scheme
    var promise_list = new PromisePool(10);
    promise_list.push(fnToGeneratePromise1);
    promise_list.push(fnToGeneratePromise2);
    promise_list.push(fnToGeneratePromise3);

    promise_list.start().then(function(results){
        console.log('all done');
    });
////}}

//{{ Scenario 2

    /* jQuery included... */
    var getUserData = function(user_id){
        return new Promise(resolve, reject) {
            $.get('getUserData.php?user_id='+user_id).then(function(rsp){
                resolve(rsp);
            });
        };
    };

    // Old Scheme
    var promise_list = [];
    promise_list.push(getUserData('user1'));
    promise_list.push(getUserData('user2'));
    // :
    // Skip lots of promise_list.push
    // :
    promise_list.push(getUserData('user100'));
    Promise.all(promise_list).then(function(results){
        console.log('all user data loaded');
    });

    // New Scheme
    var promise_list = new PromisePool(10);
    promise_list.push(getUserData.bind(this, 'user1'));
    promise_list.push(getUserData.bind(this, 'user2'));
    // :
    // Skip lots of promise_list.push
    // :
    promise_list.push(getUserData, ['user100']);
    promise_list.start().then(function(results){
        console.log('all user data loaded');
    });
//}}