lock.py

from threading import Lock, Thread
from time import sleep
import logging

logging.basicConfig(level=logging.DEBUG, format='[%(threadName)s] %(message)s')


class BackendConnection:
    _lock = Lock()

    def __enter__(self):
        logging.debug('pre acquire lock')
        self._lock.acquire()
        logging.debug('post acquire lock')
        try:
            sleep(1)
            raise RuntimeError()
        except:
            logging.debug('pre release lock on handling exception')
            self._lock.release()
            logging.debug('post release lock on handling exception')
            raise
        return True

    def __exit__(self, exc_type, exc_val, exc_tb):
        logging.debug('pre cleanup on exit')
        self._cleanup()
        logging.debug('post cleanup on exit')

    def __del__(self):
        logging.debug('pre cleanup on del')
        self._cleanup()
        logging.debug('post cleanup on del')

    def _cleanup(self):
        logging.debug('pre release lock on cleanup isLocked()')
        if BackendConnection._lock.locked():
            logging.debug('pre release lock on cleanup isLocked() = True')
            self._lock.release()
            logging.debug('post release lock on cleanup isLocked() = True')
        else:
            logging.debug('post release lock on cleanup isLocked() = False')
        logging.debug('post release lock on cleanup')


def get():
    with BackendConnection():
        pass

t1 = Thread(name='t1', target=get)
t2 = Thread(name='t2', target=get)

t1.start()
t2.start()