在python里协程使用同步锁Lock的实例
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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