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

来源：https://blog.csdn.net/caimouse/article/details/77912534