Currently calling BaseServer's shutdown() function will not make serve_forever() return immediately from it's select().

I suggest adding a new function called server_shutdown() that will make serve_forever() shutdown immediately.

Then in TCPServer(BaseServer) all we need to do is call self.socket.shutdown(socket.SHUT_RDWR) in server_shutdown()'s implementation.

To test this I made a simple script:

import threading
import time
from functools import partial
from http.server import HTTPServer, SimpleHTTPRequestHandler


def serve_http(server):
    server.serve_forever(poll_interval=2.5)

def main():
    with HTTPServer(('', 8000), SimpleHTTPRequestHandler) as server:
        t = threading.Thread(target=partial(serve_http, server))
        t.start()

        time.sleep(3)

        start = time.time()
        print('shutdown')
        server.shutdown()
        print(f'time it took: {time.time() - start}')


if __name__ == "__main__":
    main()

By the way I have to ask, if I want this feature to be merged (this is my first PR) should I make a PR to 3.6/3.7/3.8/3.9 and master?

Or should I create a PR to master only? 

thanks

> By the way I have to ask, if I want this feature to be merged (this is my first PR)

Thank you for the PR and your contribution! Unless a PR is for a problem specific to a release, simply submit a PR against the master branch. If and when a core developer chooses to merge the PR, a decision will be made about whether to backport it and we have tools to do that semi-automatically. Be aware that, since we are all volunteers here, some areas in the code base do not receive a lot of attention and http.server is one of them. So don't be discouraged if your PR is not reviewed right away. A ping down the road may help.

Just want to note that this fixes an issue in all TCPServers and not only http.server

This still leaves the open issue of UDPServer not shutting down immediately though

poke

bump