由于线程问题，Flask 应用程序无法在 Gunicorn 上运行

Question

我对 Gunicorn 完全陌生，我正在尝试在 Gunicorn 上运行我的 Flask 应用程序。我遇到的错误可以复制如下。

import threading
from flask import Flask

def perpectual_background_process():
    while True:
        True

def start_background_thread():
    global extra_thread
    extra_thread = threading.Thread(target=perpectual_background_process)
    extra_thread.start()

app = Flask(__name__)

@app.route('/')
def hello_world():
    return str(extra_thread.is_alive())

if __name__ == '__main__':
    start_background_thread()
    app.run()

当应用程序在 Flask 服务器上运行时，浏览器会正确显示

True

，但在 Gunicorn 服务器上运行时会返回以下错误。

➜ app_folder gunicorn -b 0.0.0.0:5000 app:app
[2024-01-24 22:05:11 +0800] [65632] [INFO] Starting gunicorn 21.2.0
[2024-01-24 22:05:11 +0800] [65632] [INFO] Listening at: http://0.0.0.0:5000 (65632)
[2024-01-24 22:05:11 +0800] [65632] [INFO] Using worker: sync
[2024-01-24 22:05:11 +0800] [65634] [INFO] Booting worker with pid: 65634
[2024-01-24 22:05:15,612] ERROR in app: Exception on / [GET]
Traceback (most recent call last):
  File "/opt/anaconda3/lib/python3.8/site-packages/flask/app.py", line 2528, in wsgi_app
    response = self.full_dispatch_request()
  File "/opt/anaconda3/lib/python3.8/site-packages/flask/app.py", line 1825, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/opt/anaconda3/lib/python3.8/site-packages/flask/app.py", line 1823, in full_dispatch_request
    rv = self.dispatch_request()
  File "/opt/anaconda3/lib/python3.8/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/Users/my_name/Downloads/testing/app.py", line 17, in hello_world
    return str(extra_thread.is_alive())
NameError: name 'extra_thread' is not defined

似乎应用程序无法在

extra_thread

之前启动

app

。我已经做了一些研究，但我无法找到或提出解决方案来处理这个问题。如何让我的应用程序按预期运行？非常感谢您的时间和帮助！

Answer 1

你只需要在全局范围内定义

extra_thread

：

...

extra_thread

def start_background_thread():
    global extra_thread
    ...

...