POC: timeout if you wait on a lock too long

test_lock_crash.py (text/x-python), 1.59 KB, created by Anthony Basile on 2014-08-30 17:42:26 UTC

#!/usr/bin/python

import os, sys, fcntl, time, signal

lockfilename = "mylockfile"
crashfilename = "unclean_state"


def signal_handler(signal, frame):
    print('I got tired of waiting')
    sys.exit(0)


def do_lock():
    fd = os.open(lockfilename, os.O_CREAT|os.O_RDWR, 0o660)

    try:
        fcntl.lockf(fd, fcntl.LOCK_EX|fcntl.LOCK_NB)
        print("Got the lock first ... ", end='', flush=True)
    except IOError as e:
        signal.alarm(5)
        print("Someone beat us to the lock")
        fcntl.lockf(fd, fcntl.LOCK_EX)
        signal.alarm(0)
        print("Got the lock second ... ", end='', flush=True)

    if os.path.isfile(crashfilename):
        print("in an unclean state!", flush=True)
        print("Doing cleanup!", flush=True)
        os.unlink(crashfilename)
    else:
        print("in an clean state!", flush=True)

    return fd


def do_it():
    for i in range(1,6):
        print('.', end='', flush=True)
        time.sleep(1)
    print(' crash me! ', end='', flush=True)
    for i in range(1,6):
        print('.', end='', flush=True)
        time.sleep(1)
    print(flush=True)


def do_unlock(fd):
    fcntl.lockf(fd, fcntl.LOCK_UN)
    time.sleep(1)

    try:
        fcntl.lockf(fd, fcntl.LOCK_EX|fcntl.LOCK_NB)
        os.close(fd)
        os.unlink(lockfilename)
    except IOError as e:
        os.close(fd)


def main():
    signal.signal(signal.SIGALRM, signal_handler)
    fd = do_lock()
    try:
        do_it()
    except:
        print('I crashed!')
        os.close(os.open(crashfilename, os.O_CREAT|os.O_RDWR, 0o660))
    do_unlock(fd)


if __name__ == "__main__":
    main()