aiorwlock

Read write lock for asyncio . A RWLock maintains a pair of associated locks, one for read-only operations and one for writing. The read lock may be held simultaneously by multiple reader tasks, so long as there are no writers. The write lock is exclusive.

Whether or not a read-write lock will improve performance over the use of a mutual exclusion lock depends on the frequency that the data is read compared to being modified. For example, a collection that is initially populated with data and thereafter infrequently modified, while being frequently searched is an ideal candidate for the use of a read-write lock. However, if updates become frequent then the data spends most of its time being exclusively locked and there is little, if any increase in concurrency.

Note: a task that acquires the lock should be used for releasing it. Locking from one task and releasing from another one generates RuntimeError.

Implementation is almost direct port from this patch.

Example

import asyncio
import aiorwlock


async def go():
    rwlock = aiorwlock.RWLock()

    # acquire reader lock, multiple coroutines allowed to hold the lock
    async with rwlock.reader_lock:
        print('inside reader lock')
        await asyncio.sleep(0.1)

    # acquire writer lock, only one coroutine can hold the lock
    async with rwlock.writer_lock:
        print('inside writer lock')
        await asyncio.sleep(0.1)


asyncio.run(go())

Fast path

By default RWLock switches context on lock acquiring. That allows to other waiting tasks get the lock even if task that holds the lock doesn't contain context switches (await fut statements).

The default behavior can be switched off by fast argument: RWLock(fast=True).

Long story short: lock is safe by default, but if you sure you have context switches (await, async with, async for or yield from statements) inside locked code you may want to use fast=True for minor speedup.

TLA+ Specification

TLA+ specification of aiorwlock provided in this repository.

License

aiorwlock is offered under the Apache 2 license.