Flask application dies after first POST request

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I am using Flask application to accept user goals for my robot. The problem occurs when I call the service. Here is the code:

from flask import Flask, jsonify, request
from flask_pymongo import PyMongo
import json
import rospy
from path_caller import PathCaller
from tf import TransformListener
from geometry_msgs.msg import PoseStamped
from nav_msgs.srv import GetPlan


app = Flask(__name__)
#app.config['MONGO_DBNAME'] = 'prge'
app.config["MONGO_URI"] = "mongodb://user:pass@ds04505.mlab.com:29345/prge"

mongo = PyMongo(app)

@App.route('/goal', methods=['POST'])
def add_goal():
    goal = mongo.db.goal
    position = request.json['position']
    orientation = request.json['orientation']
    goal_id = goal.insert({'position' : position, 'orientation' : orientation})
    new_goal = goal.find_one({'_id' : goal_id})
    output = {'position' : new_goal['position'], 'orientation' : new_goal['orientation']}
    position_x = json.loads(position['x'])
    position_y = json.loads(position['y'])
    #call_service(position_x, position_y)

    return jsonify(output)

def create_pose_stamped(x,y,th_x,th_y):
    pose = PoseStamped()
    pose.header.stamp = rospy.Time.now()
    pose.header.frame_id = "map"
    pose.pose.position.x = x
    pose.pose.position.y = y
    pose.pose.position.z = 0.0
    pose.pose.orientation.x = 0
    pose.pose.orientation.y = 0
    pose.pose.orientation.z = th_x
    pose.pose.orientation.w = th_y
    return pose

def get_start_position():
    tf = TransformListener()
    if tf.frameExists("base_footprint") and tf.frameExists("odom"):
        print "Frames exist"
        t = tf.getLatestCommonTime("/base_link", "/map")
        p,q = tf.lookupTransform("/odom", "/base_footprint", t)
        print p
    x = 1
    y = 5.9
    z = 0
    w = 1
    return [x,y,z,w]


def call_service(x,y):
    start_vars = get_start_position()
    start = create_pose_stamped(start_vars[0], start_vars[1], start_vars[2], start_vars[3])
    end = create_pose_stamped(x,y,0,1.0)
    rospy.loginfo("The start x: %.2f, y: %.2f, the end x: %.2f, y: %.2f", start.pose.position.x, start.pose.position.y, end.pose.position.x, end.pose.position.y)
    rospy.wait_for_service('/move_base/make_plan')
    gp_service = rospy.ServiceProxy('/move_base/make_plan', GetPlan)
    try:
        response = gp_service(start, end, 1.0)
        rospy.loginfo("The path is %s", response.plan.poses)
    except rospy.ServiceException as e:
        print "Service did not process request " + str(e)




if __name__ == '__main__':
    rospy.init_node("path_planner")
    app.run(debug=True)

After I POST a goal first time, everything works as expected. But when I POST the goal second time I get this error:

Exception happened during processing of request from ('127.0.0.1', 53198)
Traceback (most recent call last):
  File "/usr/lib/python2.7/SocketServer.py", line 596, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python2.7/SocketServer.py", line 331, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.7/SocketServer.py", line 652, in __init__
    self.handle()
  File "/home/ikhsanov/.local/lib/python2.7/site-packages/werkzeug/serving.py", line 293, in handle
    rv = BaseHTTPRequestHandler.handle(self)
  File "/usr/lib/python2.7/BaseHTTPServer.py", line 340, in handle
    self.handle_one_request()
  File "/home/ikhsanov/.local/lib/python2.7/site-packages/werkzeug/serving.py", line 324, in handle_one_request
    self.raw_requestline = self.rfile.readline()
IOError: [Errno 11] Resource temporarily unavailable

This is definately due to the service call as if I comment out the service call, everything works as expected. Also, when I call it for ... (more)