Execute the callback in another thread. Wait for and return the results.

def _execute_callback(self, callback, data):
        """Execute the callback in another thread. Wait for and return the results."""
        web_client = WebClient(
            token=self.token, base_url=self.base_url, ssl=self.ssl, proxy=self.proxy
        )
        with concurrent.futures.ThreadPoolExecutor(max_workers=1) as executor:
            # Execute the callback on a separate thread,
            future = executor.submit(
                callback, rtm_client=self, web_client=web_client, data=data
            )

            while future.running():
                pass

            future.result()