在 raspberry pi 中使用 python 进行线程化以获取 gpio 输入

Question

Doubt in Threading in gpio pins raspberry pi

my self working on encoders of differential drive robot, i need to read the speed and podition of wheels using two encoders simultaneously. I have used threading library in python even though i started both the functions only the function which has been initiated at first runs while the second doesn't. I am not sure what the resson is, is there anything to be noted while using threading in gpio pins of raspberry pi 3b, if so please help and suggest a solution.

Thanks in advance

from threading import Thread
import RPi.GPIO as GPIO
import time
import datetime 

def encoder_right(t1):
  
   ...
        
def encoder_left(t1):
    
    
   ...

t1 = datetime.datetime.now()

Thread1 = Thread(target = encoder_right(t1),daemon = True)

Thread2 = Thread(target = encoder_left(t1),daemon = True)

Thread1.start()

Thread2.start()

Thread1.join()

Thread1.join()

Answer 1

When you create a new threading.Thread object, you need to pass a function to the target parameter. In your code, instead of passing the function object, you are calling the function. That is, when you write:

Thread1 = Thread(target=encoder_right(t1), daemon=True)

You are calling encoder_right(t1) ; your code never gets beyond this point because you've entered an infinite loop. You never create a thread and you never reach the lines after this code.

You want to write instead:

Thread1 = Thread(target=encoder_right, args=(t1,), daemon=True)
Thread2 = Thread(target=encoder_left, args=(t1,), daemon=True)

This way you're passing the function object in the target parameter, and the Thread object will take care of starting the function in a new thread.

---

Unrelated to your question, but you only need to call GPIO.setmode(GPIO.BCM) and GPIO.setwarnings(False) once in your program; you don't need to call that in each thread. That is, you could write instead:

def encoder_right(t1):
    ...


def encoder_left(t1):
    ...

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

t1 = datetime.datetime.now()

Thread1 = Thread(target=encoder_right, args=(t1,), daemon=True)
Thread2 = Thread(target=encoder_left, args=(t1,), daemon=True)

Thread1.start()
Thread2.start()

Thread1.join()
Thread2.join()

Also. I would avoid giving variables the same name as your functions (eg,, in your function encoder_left you also have a variable named encoder_left ). At some point this is going to cause a surprising problem when you try to reference the function and find that you're actually referencing an integer value instead.