Multiple function calls for parallel processing inside a loop - multiprocessing

Question

I wish to detect an image from my webcam and write the result whether it is moving left or right to a file. To increase the frame rate(because this project involves a lot more processing and might be run on a raspberry pi) I decided to do the file writing part through multiprocessing (which I am new to):
code:
function for multi-processing
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()
Main code:
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
Error:
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.
Can someone guide me?