python asyncio.Event.wait()不响应event.set()

python asyncio.Event.wait() not responding to event.set()

计划是使多个IO例程"同时"运行(特别是在Raspberry Pi上，操作IO引脚并同时运行SPI接口)。我尝试使用asyncio来实现这一目标。但是，我的简单试用无法运行。
这是该代码的简化版本，省略了IO引脚的详细信息：

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"""\\
Reduced problem representation:
this won't run because GPIO details have been left out
"""

import RPi.GPIO as gpio
import asyncio

GPIO_PB = 12 # Define pushbutton channel

async def payload():
""" Provides some payload sequence using asyncio.sleep()"""
#Payload action
await asyncio.sleep(1)
#Payload action
await asyncio.sleep(1)

class IOEvent(asyncio.locks.Event):
"""\\
Create an Event for asyncio, fired by a callback from GPIO
The callback must take a single parameter: a gpio channel number
"""
def __init__(self, ioChannel, loop):
super().__init__(loop = loop)
self.io = ioChannel

def get_callback(self):
"The callback is a closure that knows self when called"
def callback( ch ):
print("callback for channel {}".format(ch))
if ch == self.io and not self.is_set():
print(repr(self))
self.set()
print(repr(self))
return callback

async def Worker(loop, event):
print("Entering Worker: {}".format(repr(loop)))
while loop.is_running():
print("Worker waiting for {}".format(repr(event)))
await event.wait()
print("Worker has event")
event.clear()
await payload()
print("payload ended")

loop = asyncio.get_event_loop()

# Create an event for the button
pb_event = IOEvent( GPIO_PB, loop)

# register the pushbutton's callback
# Pushing the button calls this callback function
gpio.add_event_callback( GPIO_PB, pb_event.get_callback() )

try:
asyncio.ensure_future(Worker(loop, pb_event))
loop.run_forever()
except KeyboardInterrupt:
pass
finally:
print("Closing Loop")
loop.stop()
loop.close()

我得到的输出是这样的：

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Entering Worker: <_UnixSelectorEventLoop running=True closed=False debug=False>
Worker waiting for <__main__.IOEvent object at 0x76a2a950 [unset]>
callback for channel 12
<__main__.IOEvent object at 0x76a2a950 [unset,waiters:1]>
<__main__.IOEvent object at 0x76a2a950 [set,waiters:1]>
callback for channel 12

这些行重复显示按钮并正确触发其回调例程。第一次按预期调用set()函数。 wait()调用和set()调用使用的事件是相同的。但是在await event.wait()调用之后，永远不会出现消息" Worker has event"。

我查看了PyQt5和asyncio：从不完成收益，但是除了默认循环，我看不到其他任何循环。

为什么wait()永不返回？我怎么知道？