python thread blocked even after returning promise

[0x410c]

rpc.exports = {
    getclasses: function () {
        return new Promise(function (resolve) {

            console.log('Getting Classes');
            var classInfoList = [];
            Java.perform(function () {

                var classes = Java.enumerateLoadedClassesSync();
                for (var i = 0; i < classes.length; i++) {
                    try {
                        var jClass = Java.use(classes[i]);
                        var classInfo = {};
                        classInfo.name = classes[i];
                        classInfo.methods = jClass.class.getDeclaredMethods().map(function (f) {
                            return f.toString()
                        });
                        classInfoList.push(classInfo);
                    } catch (e) {
                        console.log(e);
                    }
                }

            });
            resolve(classInfoList);
        });
    }
}

when called from python script interface, my pyside gui hangs till the function returns!