RuntimeError: cannot join current thread

[sangyx]

I use flask_apscheduler to run a scheduled task, and the scheduled task involves a multiprocess task. What's more, I deploy my app with uwsgi, and then I get this error:

Sun Nov 20 22:39:00 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Sun Nov 20 22:39:01 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Sun Nov 20 22:39:01 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Sun Nov 20 22:39:02 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Sun Nov 20 22:39:02 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Sun Nov 20 22:39:06 2022 - SIGPIPE: writing to a closed pipe/socket/fd (probably the client disconnected) !!!
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/home/tops/lib/python3.7/concurrent/futures/thread.py", line 40, in _python_exit
    t.join()
  File "/home/tops/lib/python3.7/threading.py", line 1029, in join
    raise RuntimeError("cannot join current thread")
RuntimeError: cannot join current thread

My code is like:

from flask import Flask
import fcntl
import atexit

app = Flask(__name__)

# use a file lock to solve the problem of multiple run
scheduler_lock = False

try:
    f = open("scheduler.lock", "wb")
    fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
    scheduler_lock = True
except:
    pass

if scheduler_lock:
    import time
    from functools import partial
    from multiprocessing import Pool
    from datetime import datetime, timedelta
    from flask_apscheduler import APScheduler

    a, b, c, d = None, None, None, None

    # setting scheduler
    scheduler = APScheduler()
    # scheduler.api_enabled = True
    scheduler.init_app(app)
    scheduler.start()

    @scheduler.task('interval', id='my_job', minutes=30, next_run_time=datetime.now())
    def my_job():
        global a, b, c, d

        run_task_partial = partial(
            mp_task, a=a, b=b, c=c, d=d)

        p = Pool(worker_num)
        with Pool(worker_num) as p:
            result = p.map(run_task_partial, keys)

    def unlock():
        fcntl.flock(f, fcntl.LOCK_UN)
        f.close()


    # register unlock
    atexit.register(unlock)

# It is a normal flask app without lock
@app.route('/checkpreload.htm')
def checkpreload():
    return 'success'

@app.route('/')
def home():
    return 'Hello World'

if __name__ == '__main__':
    app.run(host='0.0.0.0', debug=True, port=7001, use_reloader=False)

And my uwsgi config is:

[uwsgi]
module = src.app
callable = app
master = true
processes = 1

socket = 127.0.0.1:7001
protocol = http
enable-threads = true
buffer-size = 327680

enable-threads = true
preload = true
lazy-apps = true

Environment:

uWSGI>=2.0.18
APScheduler==3.9.1
Flask==2.2.2
Flask-APScheduler==1.12.3

• Python version: 3.7
• Flask version: 2.2.2