Clash Royale CLAN TAG#URR8PPP

Can't set python event flag

I have been struggling the whole day with this, I'm pretty certain it's a thread problem, but I just can't figure out what's wrong. Basically, My main.py creates an instance of "Neopixel". That neopixel starts a thread that runs a led ring. Some ring animations are running for as long as a condition is met, unlike simple led blinking that don't cause problems.

To handle those conditions, well, I use an event flag. It's set to true when it's a long animation, and when another led state kicks in, it's unset so it should theoretically stop the animation as it is in a while event.is_set() loop. But... It is never cleared, even though I do clear it.

Some code:

def __init__(self):
self._logger = logging.getLogger('ProjectAlice')
self._logger.info('Initializing Project Alice')

self._leds = NeoPixels()
self._leds.onStart()
....
self._logger.info('Project Alice started')
self._leds.onConnecting()
self.greetAlice()
....
elif message.topic == self._SUB_GREETING_BACK:
self._state = State.REGISTERED
self._logger.info('- Alice greeted back, module registered')
self._leds.onConnected()


I've remove irrelevant parts but left the led part. As we see, it starts, creates an instance of Neopixels, calls onStart() for the leds, then calls onConnect(), then tries to reach the main server through mqtt. When the main server replies, I call onConnected(). But the leds always stay in "onConnect()" and never go to the "onConnected()" state. There's a print('Done') in there, that never shows, but when I ctrl-c the program, which also then executes the "onConnected" animation

Somehow, the

self._animation.clear()

in

def onConnected(self):

does not register, the animation loop never ends but this

self._logger.info('- Alice greeted back, module registered')

prints, meaning onConnected() is called

class NeoPixels(object):

def __init__(self):
self._running = True

self._ring = Adafruit_NeoPixel(num=config.settings['ringLedCount'], pin=config.settings['ringLedPin'], brightness=125, strip_type=ws.SK6812_STRIP_RGBW)
self._ring.begin()

self._queue = Queue.Queue()
self._animation = threading.Event()

threading.Thread(target=self._run).start()

def onStart(self):
self._running = True
self._animation.clear()

self._queue.put(self._start)

def onConnecting(self):
self._animation.clear()
self._queue.put(self._connecting)


def onConnected(self):
self._animation.clear()
self._queue.put(self._connected)

def _run(self):
while self._running:
func = self._queue.get()
func()

def _start(self):
for i in range(self._ring.numPixels()):
self._setPixelColorRGB(i, 255, 0, 0)
self._ring.show()
time.sleep(10 / 1000.0)

for i in range(self._ring.numPixels()):
self._setPixelColorRGB(i, 0, 0, 0)
self._ring.show()
time.sleep(10 / 1000.0)

time.sleep(0.25)

for i in range(self._ring.numPixels()):
self._setPixelColorRGB(i, 255, 0, 0)
self._ring.show()
time.sleep(1 / 1000.0)

def _connecting(self):
self._animation.set()
while self._animation.is_set():
for i in range(self._ring.numPixels()):
self._setPixelColorRGB(i, 255, 0, 0)
self._ring.show()
time.sleep(20 / 1000.0)
threading.Timer(interval=20 / 1000.0, function=self._setPixelColorRGB, args=[i, 0, 0, 0]).start()
print('done')

def _connected(self):
for i in range(self._ring.numPixels()):
self._setPixelColorRGB(i, 0, 128, 0)
self._ring.show()

time.sleep(1)
self._clear()


1 Answer
1

This very much looks like a timing issue with your queue. If the call to onConnected happens too quickly after onConnecting has been called, onConnected clears the event before onConnecting -> _connecting sets it.

onConnected

onConnecting

onConnected

onConnecting

_connecting

This is how I stripped down your class to run and test it (I removed all the LED ring stuff and added print statements to onConnected and _run)

onConnected

_run

import time, threading, queue

class NeoPixels:
def __init__(self):
self._running = True
self._queue = queue.Queue()
self._animation = threading.Event()
threading.Thread(target=self._run)

def onStart(self):
self._running = True
self._animation.clear()
self._queue.put(self._start)

def onConnecting(self):
self._animation.clear()
self._queue.put(self._connecting)

def onConnected(self):
print("called onConnected")
self._animation.clear()
self._queue.put(self._connected)


def _run(self):
while self._running:
func = self._queue.get()
print("now running ".format(func.__qualname__))
func()

def _start(self):
time.sleep(.5)

def _connecting(self):
self._animation.set()
while self._animation.is_set():
for i in range(5):
time.sleep(20 / 1000.0)
print('done')

def _connected(self):
for i in range(1):
print("connected")
time.sleep(1)


And here's how I run it:

leds = NeoPixels()
leds.onStart()
leds.onConnecting()
leds.onConnected()


Here's the output:

called onConnected
now running NeoPixels._start
now running NeoPixels._connecting


As you can see, onConnected is called and clears the event before _run even fetched _start from the queue and processed it. So when onConnecting is executed, _connecting sets the event and since nothing clears it after that, it keeps running indefinitely.

onConnected

_run

_start

onConnecting

_connecting

So, changing onConnected to wait for the queue to clear, like so:

onConnected

def onConnected(self):
while not self._queue.empty():
time.sleep(.1)
print("called onConnected")
self._animation.clear()
self._queue.put(self._connected)


will lead to the following output:

now running NeoPixels._start
now running NeoPixels._connecting
called onConnected
done
now running NeoPixels._connected
connected


Out of curiosity, how do you actually terminate/join the thread? You create it anonymously, so I don't see how you would get a handle on it to close it once done.

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