How to avoid double checks with asyncio.Lock

I have a piece of code, that checks if the redis db has data updates and loads them to the memory. I want only one corouitine to execute this load.

class MyService:
    def __init__(self):
        self.lock = asyncio.Lock()
        self.latest_timestamp = None

    async def _check_latest_timestamp_from_db(self):
        # go to db

    async def ensure_update_loaded():
        latest_timestamp_from_db = await self._check_latest_timestamp_from_db()
        if self.timestamp == latest_timestamp_from_db:
            return
        if self.lock.locked():
            return # the load is in progress, we're okay to use the old data for now
        async with self.lock:
            # do the load
            self.timestamp = latest_timestamp_from_db

From my understanding multiple coroutines can go simultaneously to this line: async with lock:, after all the checks are passed. Yes, they will execute consequently, but the load will happen more than once. I could double check within the lock:

async with self.lock:
    if self.timestamp == latest_timestamp_from_db:
            return
    # do the load
    self.timestamp = latest_timestamp_from_db

But I think there should be a clearer solution to my problem.

You're basically implementing a double-checked locking.

Pseudocode:

class MyService:
    def __init__(self):
        self.lock = asyncio.Lock()
        self.latest_timestamp = None

    async def _check_latest_timestamp_from_db(self):
        ...


    async def ensure_update_loaded(self):
        latest_timestamp_from_db = await self._check_latest_timestamp_from_db()
        if self.latest_timestamp == latest_timestamp_from_db:
            return

        async with self.lock:
            if self.latest_timestamp == latest_timestamp_from_db:
                return

            ...

            self.latest_timestamp = latest_timestamp_from_db

Moving the check inside the lock is correct.