UDP socket can not be closed on Windows7

OS: Windows7

Qt: 5.15.1

Steps:

1, Start the routing remote access service .

2,Open the example :"multicastsender" in Qt's Example folder. compile and run it. 

3,Set the ttl to 2 , and start.

4, close the app.

The app can not exit. 

I added udpScoket4.close() in destructor of "Sender", and I found that, the close() function can not return. 

This problem only occur on Windows7. On Windows 10 , it is OK.