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 asyncioimport 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 coroutineslock acquired: Truewaiting for coroutinescoro1 waiting for the lockcoro2 waiting for the lockcallback releasing lockcoro1 acquired lockcoro1 released lockcoro2 acquired lockcoro2 released lock

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