asyncio-multilock 0.2.0

asyncio shared/exclusive mode lock

asyncio-multilock

asyncio_multilock provides MultiLock, an asyncio based lock with built-in shared/exclusive mode semantics.

MultiLock.locked can be in one of three states:

1. MultiLockType.NONE - not acquired;
2. MultiLockType.SHARED - acquired one or more times in shared mode;
3. MultiLockType.EXCLUSIVE - acquired one time in exclusive mode.

When a lock is acquired, a Hashable handle is returned which uniquely identifies the acquisition. This handle is used to release the acquisition.

from asyncio import create_task, sleep
from asyncio_multilock import MultiLock, MultiLockType

lock = MultiLock()
assert not lock.locked

shared1 = await lock.acquire(MultiLockType.SHARED)
assert lock.locked is MultiLockType.SHARED

shared2 = await lock.acquire(MultiLockType.SHARED)

async def wait_release_shared(delay: float) -> None:
    await sleep(delay)
    lock.release(shared1)
    lock.release(shared2)
create_task(wait_release_shared(3))

# Acquisition context manager.
async with lock.context(MultiLockType.EXCLUSIVE) as exclusive:
    # Blocked for 3 seconds.
    assert lock.locked is MultiLockType.EXCLUSIVE

The lock can also be acquired synchronously, returning no handle if the acquisition fails.

from asyncio_multilock import MultiLock, MultiLockType

lock = MultiLock()
assert not lock.locked

shared = lock.acquire_nowait(MultiLockType.SHARED)
assert shared

exclusive = lock.acquire_nowait(MultiLockType.EXCLUSIVE)
assert not exclusive

assert lock.locked is MultiLockType.SHARED

The lock can also be monitored for when a given lock type is next acquirable.

from asyncio_multilock import MultiLock, MultiLockType

lock = MultiLock()

async with lock.notify(MultiLockType.SHARED) as event:
    await event.wait()
    print("shared lock is acquirable")
    event.clear()