このモジュールはunixシステムにしかありません.windowsにはありません.
ドキュメントのアドレス:
https://docs.python.org/3.7/library/fcntl.html
https://www.docs4dev.com/docs/zh/python/3.7.2rc1/all/library-fcntl.html
マルチプロセスサンプルプログラム

import fcntl
import os
import time
from multiprocessing import Pool

def worker():
    print('task: %s' % os.getpid())
    try:
        f = open('scheduler.lock', 'wb')
        '''  ，   ，           '''
        fcntl.flock(f, fcntl.LOCK_EX)
        print('I am get file %s' % os.getpid())
        time.sleep(10)
        '''  '''
        fcntl.flock(f, fcntl.LOCK_UN)
        f.close()
    except Exception as e:
        print('file is already locked: %s' % os.getpid())

if __name__ == '__main__':
    p = Pool(4)
    for i in range(5):
        p.apply_async(worker)
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')

fcntl詳細パラメータ

'''f        ，operator       '''
fcntl.flock(f, operator)

fcntl.LOCK_SH    '   '
fcntl.LOCK_EX    '   '
fcntl.LOCK_NB    '    ——       ，              ，  ，          。LOCK_NB   LOCK_SH LOCK_NB     （|）    。 fcntl.flock (f,fcntl.LOCK_EX|fcntl.LOCK_NB)'
fcntl.LOCK_UN    '  '

gunicorn flask-apscheduler繰返し実行問題の解決

from flask import Flask
from service.extensions import scheduler
import logging
from logging.handlers import RotatingFileHandler
import os
import fcntl, atexit

basedir = os.path.abspath('')

def create_app():
    app = Flask(__name__)

    f = open("scheduler.lock", "wb")
    try:
        '''      '''
        fcntl.flock(f, fcntl.LOCK_EX | fcntl.LOCK_NB)
        register_apscheduler(app)
    except Exception as e:
        pass

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

    '''          ，                ，    ，   '''
    atexit.register(unlock)

    return app

def register_apscheduler(app):
    scheduler.init_app(app)
    from service import aliyuncron
    scheduler.start()

app = create_app()

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