Pooling

var Pool = Base(EventEmitter, {
    init: function(getConnection, size) {
        this._super();
        this._pool = [];
        this._queue = [];
        this.size = size;
        var me = this;
        getConnection(size, function(conn) {
            me.emit('back', conn);
        });
        this.addListener('back', function(conn) {
            var task = me._queue.shift();
            if (task) {
                task(conn);
            } else {
                me._pool.push(conn);
            }
        });
    },
    
    give: function(callback) {
        var conn = this._pool.shift();
        if (conn) {
            callback(conn);
        } else {
            this._queue.push(callback);
        }
    }
});