Thread_demo issue

[VincentDuf]

Hi nrsyed,
i'm trying to use your function and script but here is a weird error I don't understand... btw I'm using a JetsonTX2 from Nvidia.

from: can't read /var/mail/CountsPerSec
from: can't read /var/mail/VideoGet
from: can't read /var/mail/VideoShow
./thread_demo.py: 7: ./thread_demo.py: Syntax error: "(" unexpected

Other question, if i import your function in a python script i suppose i can use it normally right ?

Thanks in advance

[nrsyed]

Hi @VincentDuf,

That error sounds like it's being caused by the shell trying to execute the file (instead of running it with Python). Are you running it using the command python thread_demo.py or just thread_demo.py?

And yeah, you should be able to use it normally by importing it in a script.

Let me know if it still causes issues.

[VincentDuf]

Okay my bad you're right I tried with the sudo ./thread_demo.py
It does work well except for the putIterationPerSec part which never print the count on the frame displayed... not a big deal but still.

Other problem though: I copied your function "threadBoth" to get the frame and do some treatment before showing it.
Here is the code:

Pin1=255
setup(Pin1,'out',initial=True)
video_getter = VideoGet(source).start()
video_shower = VideoShow(video_getter.frame).start()

while True:
    if video_getter.stopped or video_shower.stopped:
       video_shower.stop()
       video_getter.stop()
       break

    frame = video_getter.frame
    hsv_im=ImageAnalyse(frame)
    mask,new_center=BoxDefinition(hsv_im)
    video_shower.frame = mask

    if cv2.waitKey(1)==ord('i'):
        set(Pin1,0)
    if cv2.waitKey(1)==ord('o'):
        set(Pin1,1)      

   
cleanup(Pin1)
cv2.destroyAllWindows()

The "setup" , "ImageAnalyse" and "BoxDefinition" function are from another python script, but the issue for me are the two last condition on cv2.waitKey. If i don't put it, the code runs correctly, but when i add it it creates problem, the window wait for me to hit a key to display another frame and after 20s it freezes totally...
I need these condition to turn on/off a GPIO pin and I don't get why it messes with the "while" loop while it shouldn't...

Thank a lot for your work !

[VincentDuf]

Hi nrsyed,
I am still waiting for an answer.. Thank you

[nrsyed]

I don't know for certain if this will help, but I found that calling cv2.waitKey() from multiple threads caused issues, which is why I ended up removing the call from my threadBoth() function and only relying on the call to cv2.waitKey() in the VideoShow class.

Can you try modifying your code by moving your calls to cv2.waitKey() to the VideoShow class instead? Or perhaps remove the call to cv2.waitKey() from VideoShow and leave the code you posted unchanged?

Let me know if this works (or if you've found another solution).

[VincentDuf]

Hi nrsyed,
I tried to remove the cv2.waitKey from the VideoShow class and I call it in my main loop as showed in the code:

#!/usr/bin/env python
import cv2
import numpy as np
import sys
from AphidFunction import image_treatment
from AphidFunction import find_aphids
from gpio import *
from VideoGet import * 
from VideoShow import *

 
button=255
setup(button,OUT)
source="nvcamerasrc ! video/x-raw(memory:NVMM), width=(int)640, height=(int)360,format=(string)I420, framerate=(fraction)30/1 ! nvvidconv flip-method=0 ! video/x-raw, format=(string)BGRx ! videoconvert ! video/x-raw, format=(string)BGR ! appsink"
video_getter = VideoGet(source).start()
video_shower = VideoShow(video_getter.frame).start()


while True:
    
    frame = video_getter.frame
    
    hsv=image_treatment(frame)
    img=find_aphids(hsv)

    video_shower.frame = img
    
    key = cv2.waitKey(10) 
    if key==ord('i'):
        set(button,1)
    if key==ord('o'):
        set(button,0)
    if key == 27:	        
	break


cleanup(button)
cap.release()
cv2.destroyAllWindows()

but I have this recuuring error:

QObject::startTimer:Timers cannot be started from another thread

I don't see what's the problem with the timer..

[nrsyed]

I'm not sure exactly what the issue is, but it's probably a thread safety issue. Will have to look into it a bit more, though I don't have experience with using gpio to run on or interact with a microcontroller (assuming that's what you're doing?).

A quick search yielded the following sources where people had the same error with OpenCV. Have you looked at these and do they seem like they might be helpful in addressing your issue?

https://stackoverflow.com/questions/42357656/pyqt5-timers-cannot-be-started-from-another-thread-error-when-changing-size-of
http://answers.opencv.org/question/160607/imshow-call-never-returns-opencv-320-dev/
tum-vision/lsd_slam#224

[yuezhilanyi]

try move all files in a folder, and move the folder into /home//.

be sure you have the read and write permissions

then cd to the folder and run

python ./thread_demo.py

[VincentDuf]

Okay thank you guys I'll have a look at all this solution.
From what I can see I'd say I have to set a main thread in which the waitKey() function will operate and synchronize the other thread with this one.
I'll have a look at the Qthread

Thanks again I'll let you know if I can make it work