pyqt 问题，求助

环境：windows Python 3.6.5 非常简单的一个 qt 应用，代码如下

from PyQt5 import QtCore
import sys
from PyQt5.QtWidgets import QApplication, QMainWindow

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(985, 635)

class MyWindow(QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super(MyWindow, self).__init__(parent)
        self.setupUi(self)
    def test(self,b):
        print(b)

app = QApplication(sys.argv)
myWin = MyWindow()


class MyThead(QtCore.QThread):
    updated = QtCore.pyqtSignal(str)

    def __init__(self, msg):
        super().__init__()
        self.msg = msg

    def run(self):
        self.updated.emit(self.msg)




#--------------后半部分
_thread = MyThead('123')
_thread.updated.connect(myWin.test)
_thread.start()
myWin.show()
app.exec()

运行起来没问题

但是如果把后面几行

_thread = MyThead('123')
_thread.updated.connect(myWin.test)
_thread.start()

放到方法里面，也就是代码后半部分变成

def _():
    _thread = MyThead('123')
    _thread.updated.connect(myWin.test)
    _thread.start()
_()
myWin.show()
app.exec()

gui 直接崩溃，也没有报错，只有一个因异常导致的 QThread: Destroyed while thread is still running

这里折腾一天了才排查到这个地方，文档也没找到相关内容...