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[英]threading.Event().wait() is not notified after calling event.set()
[英]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:
"""\
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:
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。 首次调用set()
函数。 用于wait()
调用和set()
调用的事件是相同的。 但是,在await event.wait()
调用之后,永远不会出现消息“ Worker has event” 。
我看了看PyQt5和asyncio:yield from never finishs ,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?
由add_event_callback
设置的add_event_callback
必须从不同的线程调用,因为它们是自动调用的。 这意味着您不能在asyncio.Event
上调用set
在它们之间进行同步,因为默认情况下asyncio类不是线程安全的。
要从其他线程唤醒asyncio.Event
,可以将event.set
传递给loop.call_soon_threadsafe
。 对于您的情况,您将更改:
self.set()
至:
self._loop.call_soon_threadsafe(self.set)
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