脚本终止时释放Python Flask端口

我有一个使用HTTPS的Python Flask服务器.当我按CTRL-C终止时,列表器仍然在运行(我必须在shell中运行:sudo fuser 8080/tcp -k杀死它).我想要一种更好的释放方式.有人知道使用正确的Flask代码吗？

import sys
import os
import signal
from flask import Flask, render_template, url_for, current_app, request
from OpenSSL import SSL

# Clean-up when press CTRL+C
def signal_handler(signal, frame):
        # I want to release the port here
        print('Clean-up')
        sys.exit(0)
signal.signal(signal.SIGINT, signal_handler)

context = SSL.Context(SSL.SSLv23_METHOD)
context.use_privatekey_file('server.key')
context.use_certificate_file('server.crt')

app = Flask(__name__)

@app.route("/")
def route1(arg1):
    return render_template("flask_page1.html", var1=arg1)

app.run(host="0.0.0.0", port=8080, debug=False, ssl_context=context)

Python 2.7,运行Raspbian的Raspberry Pi