第三版的generic-pool问题，按照里面的example执行的代码，但是很郁闷的是代码不能运行，单步的话，也只是到resourcePromise.then(function(client）就不执行了，这是为什么那？
使用的模块地址：https://github.com/coopernurs...
全部代码如下：

var genericPool = require('generic-pool');
var DbDriver = require('mysql');

/**
 * Step 1 - Create pool using a factory object
 */
const factory = {
    create: function(){
        return new Promise(function(resolve, reject){
            var client = DbDriver.createPool({
                host:'localhost',
                user     : 'root',
                password : 'root',
                database : 'world'});
            client.on('connected', function(){
                resolve(client)
            })
        })
    },
    destroy: function(client){
        return new Promise(function(resolve){
            client.on('end', function(){
                resolve()
            })
            client.disconnect()
        })
    }
}

var opts = {
    max: 10, // maximum size of the pool
    min: 2 // minimum size of the pool
}

var myPool = genericPool.createPool(factory, opts);

/**
 * Step 2 - Use pool in your code to acquire/release resources
 */

// acquire connection - Promise is resolved
// once a resource becomes available
var resourcePromise = myPool.acquire();

resourcePromise.then(function(client) {
    console.log('in ');
    client.query("select * from city", [], function(err,result) {
        console.log(err);
        console.log(result);
        // return object back to pool
        myPool.release(client);

    });
})
    .catch(function(err){
        // handle error - this is generally a timeout or maxWaitingClients
        // error
    });

/**
 * Step 3 - Drain pool during shutdown (optional)
 */
// Only call this once in your application -- at the point you want
// to shutdown and stop using this pool.
myPool.drain(function() {
    myPool.clear();
});