crontab 執行過慢，上次未執行完，下次就來了，加鎖處理

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import json
import logging
import os
import time
from os.path import dirname, abspath

import requests

PROJECT_DIR = dirname(dirname(dirname(abspath(__file__))))
print PROJECT_DIR
import sys

sys.path.insert(0, PROJECT_DIR)

if len(sys.argv) > 1:
    if sys.argv[1] == 'pro':
        os.environ.setdefault("DJANGO_SETTINGS_MODULE", "settings.settings_pro")
    else:
        os.environ.setdefault("DJANGO_SETTINGS_MODULE", "settings.settings_test")
else:
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "settings.settings_test")

import django
from django.conf import settings

'''
Django 版本大於等於1.7的時候，須要加上下面兩句
import django
django.setup()
不然會拋出錯誤 django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.
'''
if django.VERSION >= (1, 7):  # 自動判斷版本
    django.setup()

logger = logging.getLogger('bss')

pidfile = 'logs/bss.pid'


def clean():
    try:
        logger.info('刪除鎖文件%s', pidfile)
        if os.path.exists(pidfile):
            os.remove(pidfile)
        logger.info('刪除鎖文件%s成功', pidfile)
        return 1
    except Exception as e:
        msg = "刪除鎖文件%s失敗" % e
        logger.error(msg, exc_info=True)
        return 0


def lock():
    try:
        logger.info('建立鎖文件%s', pidfile)
        file(pidfile, 'w+').write('%s\n' % os.getpid())
        logger.info('建立鎖文件%s成功', pidfile)
    except Exception as e:
        msg = "建立鎖文件%s失敗" % e
        logger.error(msg, exc_info=True)
        sys.exit(0)


class BssService(object):
    def __init__(self):
        self.period_url = settings.BILLING_ALL_URL

    def build(self):
        logger.info("billing task begin>>>>>>>>>>>>>>>>>>")
        # do something
        logger.info("billing task   end>>>>>>>>>>>>>>>>>>")


if __name__ == "__main__":
    if not os.path.exists(pidfile):
        lock()
        bs = BssService()
        bs.build()
        status = clean()
        n = 10
        while status == 0 and n > 0:
            time.sleep(1)
            status = clean()
            n -= 1
    else:
        logger.info("其餘進程正在執行!")