Two subscribers, one with while loop, another cannot receive new ros message

Question

Hello, I am trying to make a program that starts reading camera frames with opencv and ros. Currently, I begin reading camera frames from raspberry pi camera when "start" signal is subscribed. "start" signal and opencv frame are published to another topic.

At some time, I send "end" signal to the subscriber. However, the subscriber cannot read new signal. When "start" signal came at the beginning, the callback function runs get_frame function and this function goes through while loop. So, new signals are not received at all.

class GetFrame:
def __init__(self, node_name):
    self.operate = rospy.Subscriber('operate', operate, self.callback)
    self.pub_frame = rospy.Publisher('img_camera', sendframe, queue_size=3)
    self.node_name = node_name
    self.net = None
    self.detect = None
    self.cap = None
    self.args = arg_parse()
    self.frame_data = sendframe()
    self.bridge = CvBridge()

def callback(self, data):
    if data.command == "init":
        self.initialize()
    elif data.command == "start":
        self.get_frame(data)
    elif data.command == "end":
        self.get_frame(data)

def initialize(self):
    self.net = cv2.dnn.readNetFromDarknet(self.args.config, self.args.weight)
    self.net.setPreferableBackend(cv2.dnn.DNN_BACKEND_OPENCV)
    self.net.setPreferableTarget(cv2.dnn.DNN_TARGET_CPU)

    # load DetectBoxes class
    self.detect = DetectBoxes(self.args.labels,
                              confidence_threshold=self.args.confidence,
                              nms_threshold=self.args.nmsThreshold)
    
    try:
        self.cap = cv2.VideoCapture(0)
    except IOError:
        sys.exit(1)

@staticmethod
def get_outputs_names(net):
    # names of network layers e.g. conv_0, bn_0, relu_0....
    layer_names = net.getLayerNames()
    return [layer_names[i[0] - 1] for i in net.getUnconnectedOutLayers()]

def get_frame(self, operate):
    # if start signal came before init signal
    # initialize net & camera
    if self.cap is None or not self.cap.isOpened():
        self.initialize()

    while self.cap.isOpened():
        has_frame, frame = self.cap.read()

        # if end of frame, program is terminated
        if not has_frame:
            break

        # Create a 4D blob from a frame.
        blob = cv2.dnn.blobFromImage(frame, 1 / 255, (self.args.resol, self.args.resol),
                                     (0, 0, 0), True, crop=False)

        # Set the input to the network
        self.net.setInput(blob)

        # Runs the forward pass
        network_output = self.net.forward(self.get_outputs_names(self.net))

        # Extract the bounding box and draw rectangles
        self.frame_data.percent, self.frame_data.coords = self.detect.detect_bounding_boxes(frame, network_output)

        print("FPS {:5.2f}".format(1000/elapsed))

        # publish frames + detected objects
        self.frame_data.operate = operate.command
        try:
            self.frame_data.frame = self.bridge.cv2_to_imgmsg(frame, encoding="passthrough")
            self.pub_frame.publish(self.frame_data)
        except CvBridgeError as e:
            print(e)

    self.log.publish(log_generator(self.node_name, "Camera closed"))
    # releases video and removes all windows generated by the program
    # cap.release()


 if __name__ == '__main__':
     rospy.init_node('get_frame', anonymous=True)
     g_frame = GetFrame('get_frame')
     try:
         rospy.spin()
     except KeyboardInterrupt:
         print("Shut down - keyboard interruption")

Should I stop while loop? How can I subscribe new message while not ending while loop?

Thank you

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Originally posted by henrykim on ROS Answers with karma: 3 on 2019-11-12

Post score: 0

Answer 1

Because the start is done in a other thread then the stop.

If you like to stop the start thread you have to use the "data" as an global var

So in the constructur you write

try this:

class GetFrame:
def __init__(self, node_name):
    self.operate = rospy.Subscriber('operate', operate, self.callback)
    self.pub_frame = rospy.Publisher('img_camera', sendframe, queue_size=3)
    self.node_name = node_name
    self.net = None
    self.detect = None
    self.cap = None
    self.args = arg_parse()
    self.frame_data = sendframe()
    self.bridge = CvBridge()
    self.cmd = "end"

def callback(self, data):
    self.cmd = data.command 
    if data.command == "init":
        self.initialize()
    elif data.command == "start":
        self.get_frame()


def initialize(self):
    self.net = cv2.dnn.readNetFromDarknet(self.args.config, self.args.weight)
    self.net.setPreferableBackend(cv2.dnn.DNN_BACKEND_OPENCV)
    self.net.setPreferableTarget(cv2.dnn.DNN_TARGET_CPU)

    # load DetectBoxes class
    self.detect = DetectBoxes(self.args.labels,
                              confidence_threshold=self.args.confidence,
                              nms_threshold=self.args.nmsThreshold)
    
    try:
        self.cap = cv2.VideoCapture(0)
    except IOError:
        sys.exit(1)

@staticmethod
def get_outputs_names(net):
    # names of network layers e.g. conv_0, bn_0, relu_0....
    layer_names = net.getLayerNames()
    return [layer_names[i[0] - 1] for i in net.getUnconnectedOutLayers()]

def get_frame(self):
    # if start signal came before init signal
    # initialize net & camera
    if self.cap is None or not self.cap.isOpened():
        self.initialize()

    while self.cap.isOpened():
        if self.cmd != "start"
            return

        has_frame, frame = self.cap.read()

        # if end of frame, program is terminated
        if not has_frame:
            break

        # Create a 4D blob from a frame.
        blob = cv2.dnn.blobFromImage(frame, 1 / 255, (self.args.resol, self.args.resol),
                                     (0, 0, 0), True, crop=False)

        # Set the input to the network
        self.net.setInput(blob)

        # Runs the forward pass
        network_output = self.net.forward(self.get_outputs_names(self.net))

        # Extract the bounding box and draw rectangles
        self.frame_data.percent, self.frame_data.coords = self.detect.detect_bounding_boxes(frame, network_output)

        print("FPS {:5.2f}".format(1000/elapsed))

        # publish frames + detected objects
        self.frame_data.operate = cmd
        try:
            self.frame_data.frame = self.bridge.cv2_to_imgmsg(frame, encoding="passthrough")
            self.pub_frame.publish(self.frame_data)
        except CvBridgeError as e:
            print(e)

    self.log.publish(log_generator(self.node_name, "Camera closed"))
    # releases video and removes all windows generated by the program
    # cap.release()


 if __name__ == '__main__':
     rospy.init_node('get_frame', anonymous=True)
     g_frame = GetFrame('get_frame')
     try:
         rospy.spin()
     except KeyboardInterrupt:
         print("Shut down - keyboard interruption")

---

Originally posted by duck-development with karma: 1999 on 2019-11-13

This answer was ACCEPTED on the original site

Post score: 1

---

Original comments

Comment by henrykim on 2019-11-13:
Thank you for the reply, but this didn't solve my problem. My problem is that at first Subscriber receives "start" signal so through callback function is starts get_frame function. SInce there is a while loop inside get_frame it does not end. Therefore, even though "end" signal is published the subscriber is not reading the "end" signal, it simply continues processing while loop.