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Read write lock for asyncio.

Project description

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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.

Implementation is almost direct port from this patch.

Example with async def

Requires Python 3.5+

import asyncio
import aiorwlock
loop = asyncio.get_event_loop()


async def go():
    rwlock = aiorwlock.RWLock(loop=loop)
    async with rwlock.writer:
        # or same way you can acquire reader lock
        # async with rwlock.reader: pass
        print("inside writer")
        await asyncio.sleep(0.1, loop=loop)

loop.run_until_complete(go())

Old-school way

Requires Python 3.3+

import asyncio
import aiorwlock
loop = asyncio.get_event_loop()


@asyncio.coroutine
def go():
    rwlock = aiorwlock.RWLock(loop=loop)
    with (yield from rwlock.writer):
        # or same way you can acquire reader lock
        # with (yield from rwlock.reader): pass
        print("inside writer")
        yield from asyncio.sleep(0.1, loop=loop)

loop.run_until_complete(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.

License

aiorwlock is offered under the Apache 2 license.

Changes

0.5.0 (2017-12-03)

  • Fix corner cases and deadlock when we upgrade lock from write to read #39
  • Use loop.create_future instead asyncio.Future if possible

0.4.0 (2015-09-20)

  • Support Python 3.5 and async with statement
  • rename .reader_lock -> .reader, .writer_lock -> .writer. Backward compatibility is preserved.

0.3.0 (2014-02-11)

  • Add .locked property

0.2.0 (2014-02-09)

  • Make .release() non-coroutine

0.1.0 (2014-12-22)

  • Initial release

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