class ThreadedCamera(object):
    def __init__(self, source=0):
        global cap
        self.capture = cv2.VideoCapture(source)
 
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True  # 防止主线程挂掉，子线变成程僵尸进程
        self.thread.start()
 
        self.status = False
        self.frame = None
 
    def update(self):
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()
 
    def grab_frame(self):
        if self.status:
            return (self.status,self.frame)
        return (None,None)
        
streamer = ThreadedCamera(args.video)
while True:#cv.waitKey(1) != 'q':
    has_frame, show = streamer.grab_frame()