multiprocessing - 多个函数调用循环内的并行处理

Question

我希望从我的网络摄像头检测图像并将结果写入文件，无论它是向左还是向右移动。为了提高帧速率（因为这个项目涉及更多的处理并且可能在树莓派上运行）我决定通过多处理（我是新手）来完成文件写入部分：

代码：

多处理功能

def send_cmd(cv):
    # ####EXECUTE LOGIC AND CREATE COMMAND###
# writing to file
# just a sample command// change as will
dictionary = {'left': 0, 'right': 0, 'stop': 0}

        if cv[0] == 'left':
            dictionary['right'] = 1
        else:
            dictionary['left'] = 1

cmd = '{"left":' + str(dictionary['left']) + ',"right":' + str(dictionary['left'
        ]) + ',"stop":' + str(dictionary['left']) + '}'
print("command written: " + cmd)
f = open('command.txt', 'w')
f.write(cmd)
f.close()

主要代码：

while True:
    try:
        frame = cv.VideoCapture(0)
        frame = imutils.resize(frame, width=400)

    if W is None or H is None:
        (H, W) = frame.shape[:2]

    blob = cv.dnn.blobFromImage(cv.resize(frame, (300, 300)),
                                0.007843, (300, 300), 127.5)
    net.setInput(blob)
    detections = net.forward()
    rects = []

    for i in range(0, detections.shape[2]):

        if detections[0, 0, i, 2] > args['confidence']:
            box = detections[0, 0, i, 3:7] * np.array([W, H, W, H])
            rects.append(box.astype('int'))

            (startX, startY, endX, endY) = box.astype('int')
            cv.rectangle(frame, (startX, startY), (endX, endY), (0,
                         0xFF, 0), 2)

    objects = ct.update(rects)

    for (objectID, centroid) in objects.items():

        text = 'ID {}'.format(objectID)
        cv.putText(
            frame,
            text,
            (centroid[0] - 10, centroid[1] - 10),
            cv.FONT_HERSHEY_SIMPLEX,
            0.5,
            (0, 0xFF, 0),
            2,
            )
        cv.circle(frame, (centroid[0], centroid[1]), 4, (0, 0xFF,
                  0), -1)
        center = (centroid[0], centroid[1])
        pts.appendleft(center)

        for i in np.arange(1, len(pts)):

            if pts[i - 1] is None or pts[i] is None:
                continue

            if counter >= 10 and i == 1 and pts[-1] is not None:
                dX = pts[-1][0] - pts[i][0]
                dY = pts[-1][1] - pts[i][1]
                global dirX
                global dirY
                (dirX, dirY) = ('', '')

                if np.abs(dX) > 20:
                    dirX = ('left' if np.sign(dX) == 1 else 'right')

                if np.abs(dY) > 20:
                    dirY = ('up' if np.sign(dY) == 1 else 'down')

                #tried multiprocessing with process method but to many process calls at the same time
                order = multiprocessing.Process(target = send_cmd,args = ([dirX, dirY]))
                order.start()
                order.join()

                # send_cmd(cv=[dirX, dirY], us=ultra_sonic)


                if dirX != '' and dirY != '':
                    direction = '{}-{}'.format(dirY, dirX)
                else:

                    direction = (dirX if dirX != '' else dirY)

            thickness = int(np.sqrt(args['buffer'] / float(i + 1))
                            * 2.5)

        cv.putText(
            frame,
            direction,
            (10, 30),
            cv.FONT_HERSHEY_SIMPLEX,
            0.65,
            (0, 0, 0xFF),
            3,
            )
        cv.putText(
            frame,
            'dx: {}, dy: {}'.format(dX, dY),
            (10, frame.shape[0] - 10),
            cv.FONT_HERSHEY_SIMPLEX,
            0.35,
            (0, 0, 0xFF),
            1,
            )

    cv.imshow('Frame', frame)
    key = cv.waitKey(1) & 0xFF
    counter += 1

错误：

 RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.

有人可以指导我吗？

标签： multiprocessingruntime-errorpython-multiprocessing