Не срабатывает сигнал

import requests, sys, threading
from PyQt4 import QtGui, QtCore
 
links = ["http://google.com/", "http://yandex.ru/", "http://mail.ru/", "http://vk.com/", "http://microsoft.com/", "http://ubuntu.com/", "http://tass.ru/"]
 
def thread(my_func):
 
    def wrapper(*args, **kwargs):
        my_thread = threading.Thread(target=my_func, args=args, kwargs=kwargs)
        my_thread.start()
    return wrapper
 
@thread
def doit(signal, curr):
    get = requests.get(links[curr],timeout=3)
    signal.emit()
 
class MThread(QtCore.QObject):
    trigger = QtCore.pyqtSignal()
 
    def start(self):
        self.trigger.connect(self.handle_trigger,QtCore.Qt.QueuedConnection)
        for i in range(len(links)):
            doit(self.trigger,i)
 
    def handle_trigger(self):
        print "trigger signal received"
 
th = MThread()
th.start()

import sys
import threading
 
import requests
 
from PyQt4 import QtGui, QtCore
 
 
def thread(my_func):
 
    def wrapper(*args, **kwargs):
        my_thread = threading.Thread(target=my_func, args=args, kwargs=kwargs)
        my_thread.start()
    return wrapper
 
 
@thread
def doit(signal, url):
    data = requests.get(url)
    signal.emit(data.text)
 
 
class Downloader(QtCore.QObject):
    download_complete = QtCore.pyqtSignal(str, name='worker_complete')
 
    def __init__(self):
        super().__init__()
        self.count_complete = 0
 
        self.links = [
            "http://google.com/", "http://yandex.ru/", "http://mail.ru/",
            "http://vk.com/", "http://microsoft.com/", "http://ubuntu.com/",
            "http://tass.ru/"
        ]
 
        self.download_complete.connect(self.handle_complete,
                                       QtCore.Qt.QueuedConnection)
        self.download()
 
    def download(self):
        for i in self.links:
            doit(self.download_complete, i)
 
    def handle_complete(self, data):
        print(data[:30], '\n')
        self.count_complete += 1
        if self.count_complete == len(self.links):
            exit()
            
 
app = QtCore.QCoreApplication(sys.argv)
worker = Downloader()
app.exec()

super(Downloader, self).__init__()

app = QtCore.QCoreApplication(sys.argv)
...
...
app.exec_()