publish() to a closed topic when publishing a marker

edit

Hello guys! I am trying to subscribe a message (/position) and publish a marker. The message(/position) contains series of (x,y,z) as below :

...
---
x: -253.021528805
y: -545.031320081
z: -465.328910428   
---
x: -305.591390007
y: -578.07464085
z: -511.685201552
---
...

Below is my code :

#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Point, Vector3
from visualization_msgs.msg import Marker


def callback(position):
  marker_pub = rospy.Publisher('route', Marker, queue_size = 100)

  while not rospy.is_shutdown() :
    # print(pos_vec)
    marker = Marker()
    marker.header.frame_id = '/map'
    marker.type = marker.LINE_STRIP
    marker.action = marker.ADD

    #Marker scale
    marker.scale.x = 0.1
    marker.scale.y = 0.1
    marker.scale.z = 0.1

    #Marker color
    marker.color.a = 1.0
    marker.color.r = 1.0
    marker.color.g = 1.0
    marker.color.b = 0.0

    #Marker orientation
    marker.pose.orientation.x = 0.0
    marker.pose.orientation.y = 0.0
    marker.pose.orientation.z = 0.0
    marker.pose.orientation.w = 1.0

    #Marker line points
    marker.points = []
    p = Point()
    p.x = position.x
    p.y = position.y
    p.z = position.z
    marker.points.append(p)

    #Publish the marker
    marker_pub.publish(marker)

if __name__ == "__main__" :
rospy.init_node("marker_publisher")
rospy.Subscriber("/position", Vector3, callback)
rospy.spin()

However, I got the following errors :

[ERROR] [1521469185.321377]: bad callback: <function draw at 0x7f184ad9cb18>
Traceback (most recent call last):
File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 750, in _invoke_callback
cb(msg)
File "/home/parallels/SDC_ws/src/simon/src/marker.py", line 45, in draw
marker_pub.publish(marker)
File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 882, in publish
self.impl.publish(data)
File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 1041, in publish
raise ROSException("publish() to a closed topic")
ROSException: publish() to a closed topic

I have searched the Internet but it seems very few people had encountered this kind of problem. Can anyone give me some hint? Thank you! Sorry for any grammar mistakes.