python里使用Condition对象来唤醒指定数量的协程

在asyncio库里，定义Condition对象，它的行为与事件Event有点像，区别是事件是通知所有对象，Condition对象可以指定一定数量的协程被通知，它是通过函数notify()来实现的，如果参数里放2，就是通知两个协程，例子如下：

import asyncio


async def consumer(condition, n):
    with await condition:
        print('consumer {} is waiting'.format(n))
        await condition.wait()
        print('consumer {} triggered'.format(n))
    print('ending consumer {}'.format(n))


async def manipulate_condition(condition):
    print('starting manipulate_condition')

    # pause to let consumers start
    await asyncio.sleep(0.1)

    for i in range(1, 3):
        with await condition:
            print('notifying {} consumers'.format(i))
            condition.notify(n=i)
        await asyncio.sleep(0.1)

    with await condition:
        print('notifying remaining consumers')
        condition.notify_all()

    print('ending manipulate_condition')


async def main(loop):
    # Create a condition
    condition = asyncio.Condition()

    # Set up tasks watching the condition
    consumers = [
        consumer(condition, i)
        for i in range(5)
    ]

    # Schedule a task to manipulate the condition variable
    loop.create_task(manipulate_condition(condition))

    # Wait for the consumers to be done
    await asyncio.wait(consumers)


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

starting manipulate_condition
consumer 2 is waiting
consumer 3 is waiting
consumer 4 is waiting
consumer 1 is waiting
consumer 0 is waiting
notifying 1 consumers
consumer 2 triggered
ending consumer 2
notifying 2 consumers
consumer 3 triggered
ending consumer 3
consumer 4 triggered
ending consumer 4
notifying remaining consumers
ending manipulate_condition
consumer 1 triggered
ending consumer 1
consumer 0 triggered
ending consumer 0

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