Question

计划是让几个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来实现这一点。但是，我的简单试用拒绝运行这是代码的简化版本，省略了IO引脚细节：

"""\
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

这些行反复显示按钮并正确触发其回调例程。第一次按预期调用set()功能。用于wait()呼叫和set()呼叫的事件是相同的。但是await event.wait()来电之后，“工人有事件”的消息就会出现。

我看了PyQt5 and asyncio: yield from never finishes，但是我没有看到任何其他循环而不是默认循环。

为什么wait()永远不会回来？我怎么能找到？

Answer 1

由add_event_callback设置的回调必须从不同的线程调用，因为它们是在不自动调用的情况下调用的。这意味着您无法在set上调用asyncio.Event来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。

要从其他主题中唤醒asyncio.Event，您可以将event.set传递给loop.call_soon_threadsafe。在您的情况下，您将更改：

self.set()

为：

self._loop.call_soon_threadsafe(self.set)

python asyncio.Event.wait（）没有响应event.set（）

1 个答案: