我有办法了，看看：

import queue
import threading

class Worker:
    def __init__(self):
        self.queue = queue.Queue()
        threading.Thread(target=self._worker).start()

    def _worker(self):
        print("starting thread")
        while True:
            record = self.queue.get()
            if record is None:
                print("exiting")
                break
            print(f"Got message: {record}")

    def emit(self, record):
        self.queue.put(record)

class Wrapper:
    def __init__(self):
        self._worker = Worker()

    def __del__(self):
        print("Wrapper is being deleted")
        self._worker.emit(None)

    def emit(self, record):
        self._worker.emit(record)

def main():
    worker = Wrapper()
    worker.emit("foo")
    worker.emit("bar")
    print("main exits")

if __name__ == "__main__":
    main()

这里的要点是，当main退出时，worker（Wrapper的一个示例）将超出作用域，它的__del__方法将被调用，并且它将向一个真实的的工作对象发送停止消息。
运行此代码的结果（当然，“Got message”行可以位于不同的位置）：

starting thread
main exits
Wrapper is being deleted
Got message: foo
Got message: bar
exiting

正如avysk所指出的，问题很可能是atexit处理程序触发得太晚，在等待非守护进程线程已经（应该）完成之后，这会导致死锁。
如果我是你，我只会在if __name__ == '__main__'块的末尾添加一个类似TeamsHandler.finish()的调用，并沿着以下代码行修改TeamsHandler（未测试）：

_queues = []

class TeamsHandler(StreamHandler):
    def __init__(self, channel_url):
        super().__init__()
        self.channel_url = channel_url
        self.queue = queue.Queue()
        self.thread = threading.Thread(target=self._worker)
        self.thread.start()
        _queues.append(self.queue)

    def _worker(self):
        while True:
            record = self.queue.get()
            if record is None:
                break
            msg = self.format(record)
            print(msg)

    def emit(self, record):
        # enqueue the record to log and return control to the caller
        self.queue.put(record)

    @staticmethod
    def finish(self):
        for q in _queues:
            q.put(None)
        del _queues[:]

为了确保线程在程序结束时结束，应该将其设置为守护线程，这样就不需要任何atexit的东西，因为它启动得不够早，所以根本不起作用。

class TeamsHandler(StreamHandler):
    def __init__(self, channel_url):
        super().__init__()
        self.channel_url = channel_url
        self.queue = queue.Queue()
        self.thread = threading.Thread(target=self._worker)
    
        self.thread.setDaemon(True)  # INSERT THIS LINE
    
        self.thread.start()

# ...