Asnycio Lock에 대해 알아보자.

• asyncio는 한 개의 쓰레드에서 돌아가지만, 동시성이 존재한다. 이 때문에, 잘 못 쓰면 작업들이 예상치 못한 순서로 일어날 수도 있다.
• threading이나 multiprocessing에서와 같은 Lock을 사용하면 예기치 못한 상황을 예방할 수 있다. (save concurrency)

Example

---

Without Lock

import asyncio
import random

owner = None


async def coro1():
    global owner

    owner = 'IAMMAN'
    print(f"I am owner, {owner}")
    await asyncio.sleep(random.random())
    print(f"{owner} is man.")


async def coro2():
    global owner

    owner = 'IAMWOMAN'
    print(f"I am owner, {owner}")
    await asyncio.sleep(random.random())
    print(f"{owner} is woman.")


async def main(loop):
    while True:
        await asyncio.gather(coro1(), coro2())
        await asyncio.sleep(0.1)


if __name__ == "__main__":
    event_loop = asyncio.get_event_loop()
    try:
        event_loop.run_until_complete(main(event_loop))
    finally:
        event_loop.close()

Result

I am owner, IAMMAN
I am owner, IAMWOMAN
IAMWOMAN is woman.
IAMWOMAN is man.
I am owner, IAMMAN
I am owner, IAMWOMAN
IAMWOMAN is woman.
IAMWOMAN is man.
I am owner, IAMMAN
I am owner, IAMWOMAN
IAMWOMAN is man.
IAMWOMAN is woman.
...

→ 보는것 처럼 마구잡이로 섞여있다.

With Lock

import asyncio
import random

owner = None


async def coro1(lock):
    global owner

    await lock.acquire()
    owner = 'IAMMAN'
    print(f"I am owner, {owner}")
    await asyncio.sleep(random.random())
    print(f"{owner} is man.")
    lock.release()


async def coro2(lock):
    global owner

    async with lock:
        owner = 'IAMWOMAN'
        print(f"I am owner, {owner}")
        await asyncio.sleep(random.random())
        print(f"{owner} is woman.")


async def main(loop):
    lock = asyncio.Lock()

    while True:
        await asyncio.gather(coro1(lock), coro2(lock))
        await asyncio.sleep(0.1)


if __name__ == "__main__":
    event_loop = asyncio.get_event_loop()
    try:
        event_loop.run_until_complete(main(event_loop))
    finally:
        event_loop.close()

결과

I am owner, IAMMAN
IAMMAN is man.
I am owner, IAMWOMAN
IAMWOMAN is woman.
I am owner, IAMMAN
IAMMAN is man.
I am owner, IAMWOMAN
IAMWOMAN is woman.
I am owner, IAMMAN
IAMMAN is man.
I am owner, IAMWOMAN
IAMWOMAN is woman.
I am owner, IAMMAN

→ 의도했던 결과가 나온다.

• 위의 예제만 보면 이럴거면 굳이 왜 비동기로 짜냐고 생각할 수 있지만, 복잡한 코드 속에서 필요한 부분만 적재적소에 Lock을 사용해주면 더욱 안정성있는 프로그램을 만들 수 있다.