Lock extend should be able to take new timeout value

[thomasst]

Instead of adding "additional time" to the lock, it should be possible to specify a new timeout for the lock. Consider the following use case:

while perform_operation(): # usually completes quickly, but should not take longer than N seconds
    lock.extend(N)

In this example, I'd want the lock to expire after no more than N seconds, regardless of how quickly the operation completes. With the current lock implementation this isn't possible. There should be a separate method or argument which indicates that the passed time is the new timeout value (as opposed to being added to the current timeout value).

[xush6528]

I want it too!

Now I have to wrap the Lock class.

class MyLock(Lock):
    def __init__(self, *args, **kwargs):
        super(MyLock, self).__init__(*args, **kwargs)

    def expire(self, new_expire_time):
        """
        Reset expire time to an already acquired lock.

        ``new_expire_time`` can be specified as an integer or a float, both
        representing the number of seconds to add.
        """
        if self.local.token is None:
            raise LockError("Cannot extend an unlocked lock")
        if self.timeout is None:
            raise LockError("Cannot extend a lock with no timeout")
        return self.do_extend(new_expire_time)

    def do_expire(self, new_expire_time):
        pipe = self.redis.pipeline()
        pipe.watch(self.name)
        lock_value = pipe.get(self.name)
        if lock_value != self.local.token:
            raise LockError("Cannot extend a lock that's no longer owned")
        pipe.multi()
        pipe.pexpire(self.name, int(new_expire_time * 1000))

        try:
            response = pipe.execute()
        except WatchError:
            # someone else acquired the lock
            raise LockError("Cannot extend a lock that's no longer owned")
        if not response[0]:
            # pexpire returns False if the key doesn't exist
            raise LockError("Cannot extend a lock that's no longer owned")
        return True

Then

redis_client = Redis(...)
redis_client.lock(name, lock_class=MyLock)

[andymccurdy]

This has been merged in d127929. It will go out to PyPI with the next version.