Multiple processes are being called in order to access a single webcam

[ali0806]

It gives a error "can't open camera by index"

[ali0806]

It is happen because In Python's multiprocessing module, each process runs in its own separate memory space, so it's possible for two processes to try to open the same camera without being aware of each other.

For resolve this problem, you can use a Lock or a Value object to synchronize access to the camera, or use a process manager like concurrent.futures.ProcessPoolExecutor to control the number of processes running at the same time.

Here in concurrent.futures.ProcessPoolExecutor(n) we can pass the number of processes running at the same time. This will resolve our probelm

[ali0806]

In multiprocessing, i can't access camera from the constructor. I need to define camera in get_frame. For example,

class resizer:
    def __init__(self):
        self.cap = cv2.VideoCapture(0)
    def image_resize(self):
        succ, image = self.cap.read()
        image = cv2.resize(image, (224, 224))
        image = image.astype(np.float32)
        image /= 255.0
        return image

if __name__ == '__main__':
    with concurrent.futures.ProcessPoolExecutor(1) as excutor:
        future1=excutor.submit(resizer().image_resize)
        future2=excutor.submit(resizer().image_resize)
        future3=excutor.submit(resizer().image_resize)
        future4=excutor.submit(resizer().image_resize)
    cv2.imshow('a',future1.result())
    cv2.imshow('b',future2.result())
    cv2.imshow('c',future3.result())
    cv2.imshow('d',future4.result())
    cv2.waitKey(0)

Here I can't open camera. To open the camera I need to initialize self.cap =cv2.VideoCapture(0)` inside theimage_resize` function.

def image_resize(self):
        self.cap = cv2.VideoCapture(0)
        succ, image = self.cap.read()
        image = cv2.resize(image, (224, 224))
        image = image.astype(np.float32)
        image /= 255.0
        return image

[ali0806]

Article for multiprocessing: https://superfastpython.com/processpoolexecutor-in-python/

[ali0806]

Why i can't access camera from constructor? @shivazi22 dada

[ali0806]

content : https://towardsdatascience.com/multiprocessing-in-python-9d498b1029ca