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

Question

该计划是让多个 IO 例程“同时”运行（特别是在 Raspberry Pi 上，同时操作 IO 引脚并运行 SPI 接口）。我尝试使用 asyncio 来实现这一点。然而，我的简单尝试拒绝运行。
这是代码的简化版本，省略了 IO 引脚详细信息：

"""\
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

这些行显示按钮重复并正确触发其回调例程。第一次它set()按预期调用该函数。wait()调用和调用所使用的事件set()是相同的。但呼叫后从未出现消息“Worker has event”await event.wait()。

我查看了PyQt5 和 asyncio：yield from never finish，但除了默认循环之外，我没有看到任何其他循环。

为什么wait()一去不复返？我怎么知道呢？

Answer 1

设置的回调add_event_callback是从不同的线程调用的，正如它们在“后台”自动调用所指示的那样。这意味着您无法直接从 GPIO 回调set调用asyncio.Event，因为 asyncio 类不是线程安全的。

要从不同的线程唤醒asyncio.Event，您可以传递event.set到loop.call_soon_threadsafe。在你的情况下，你会改变：

self.set()

到：

self._loop.call_soon_threadsafe(self.set)