aioredis-lock 0.1.0

Wrapper to provide distributed locks in aioredis

aioredis_lock

Implementation of distributed locking with aioredis, an asyncio based redis client.

This is a standalone lib until, and if, aio-libs/aioredis#573 is accepted.

Usage

You need an aioredis.RedisConnection or aioredis.ConnectionsPool already created.

Mutex

from aioredis_lock import RedisLock, LockTimeoutError

try:
    async with RedisLock(
        pool,
        key="foobar",
        # how long until the lock should expire (seconds). this can be extended
        # via `await lock.extend(30)`
        timeout=30,
        # you can customize how long to allow the lock acquisitions to be
        # attempted.
        wait_timeout=30,
    ) as lock:
        # If you get here, you now have a lock and are the only program that
        # should be running this code at this moment.

        # do some work...

        # we may want it longer...
        await lock.extend(30)

except LockTimeoutError:
    # The lock could not be acquired by this worker and we should give up
    pass

Simple Leader/Follower(s)

Let's suppose you need a simple leader/follower type implementation where you have a number of web-workers but just want 1 to preform a repeated task. In the case the leader fails someone else should pick up the work. Simply pass wait_timeout=None to RedisLock allowing the worker to keep trying to get a lock for when the leader eventually fails. The main complication here is extending the lock and validating the leader still owns it.

from aioredis_lock import RedisLock

# if the lock is lost, we still want to be a follower
while True:

    # wait indefinitely to acquire a lock
    async with RedisLock(pool, "shared_key", wait_timeout=None) as lock:

        # hold the lock as long as possible
        while True:
            if not await lock.is_owner():
                logger.debug("We are no longer the lock owner, falling back")
                break

            # do some work

            if not await lock.renew():
                logger.debug("We lost the lock, falling back to follower mode")
                break

This mostly delegates the work of selecting and more importantly promoting leaders.