python里协程使用同步锁Lock

尽管asyncio库是使用单线程来实现协程的，但是它还是并发的，乱序执行的。可以说是单线程的调度系统，并且由于执行时有延时或者I/O中断等因素，每个协程如果同步时，还是得使用一些同步对象来实现。
比如asyncio就定义了一个锁对象Lock，它一次只允许一个协程来访问共享的资源，如果多协程想访问就会阻塞起来，也就是说如果一个协程没有释放这个锁，别的协程是没有办法访问共享的资源。

例子：

import asyncio
import functools


def unlock(lock):
    print('callback releasing lock')
    lock.release()


async def coro1(lock):
    print('coro1 waiting for the lock')
    with await lock:
        print('coro1 acquired lock')
    print('coro1 released lock')


async def coro2(lock):
    print('coro2 waiting for the lock')
    await lock
    try:
        print('coro2 acquired lock')
    finally:
        print('coro2 released lock')
        lock.release()


async def main(loop):
    # Create and acquire a shared lock.
    lock = asyncio.Lock()
    print('acquiring the lock before starting coroutines')
    await lock.acquire()
    print('lock acquired: {}'.format(lock.locked()))

    # Schedule a callback to unlock the lock.
    loop.call_later(0.1, functools.partial(unlock, lock))

    # Run the coroutines that want to use the lock.
    print('waiting for coroutines')
    await asyncio.wait([coro1(lock), coro2(lock)]),


event_loop = asyncio.get_event_loop()
try:
    event_loop.run_until_complete(main(event_loop))
finally:
    event_loop.close()

输出结果如下：

acquiring the lock before starting coroutines
lock acquired: True
waiting for coroutines
coro1 waiting for the lock
coro2 waiting for the lock
callback releasing lock
coro1 acquired lock
coro1 released lock
coro2 acquired lock
coro2 released lock

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