title: WARN:0 terminating async callback error in cv2
body: <p>i stuck in below code please help me to solve error which is  WARN:0 terminating async callback error in cv2</p>
  
  <pre><code># this is a client program which run on client side
  import cv2
  import socket
  import numpy as np
  import math
  import time
  
  
  try:
      start_time = time.time()
      state1 = "off"
      state2 = "off"
      state3 = "off"
      mode = "on"
      host = "192.168.0.106" # socket which acording server in our case #ip address of  rapberry Pi 
      port = 9345
      mySocket = socket.socket()
      mySocket.connect((host,port))
      cap = cv2.VideoCapture(0)
      while(cap.isOpened()):
      # read image
          ret, img = cap.read()
  
      # get hand data from the rectangle sub window on the screen
          cv2.rectangle(img, (300,300), (100,100), (0,255,0),0)
          crop_img = img[100:300, 100:300]
  
      # convert to grayscale
          grey = cv2.cvtColor(crop_img, cv2.COLOR_BGR2GRAY)
  
      # applying gaussian blur
          value = (35, 35)
          blurred = cv2.GaussianBlur(grey, value, 0)
  
      # thresholdin: Otsu's Binarization method
          _, thresh1 = cv2.threshold(blurred, 127, 255,
                                 cv2.THRESH_BINARY_INV+cv2.THRESH_OTSU)
  
      # show thresholded image
          cv2.imshow('Thresholded', thresh1)
  
      # check OpenCV version to avoid unpacking error
          (version, _, _) = cv2.__version__.split('.')
  
          if version == '3':
              image, contours, hierarchy = cv2.findContours(thresh1.copy(), \
                     cv2.RETR_TREE, cv2.CHAIN_APPROX_NONE)
          elif version == '2':
              contours, hierarchy = cv2.findContours(thresh1.copy(),cv2.RETR_TREE, \
                     cv2.CHAIN_APPROX_NONE)
  
      # find contour with max area
          cnt = max(contours, key = lambda x: cv2.contourArea(x))
  
      # create bounding rectangle around the contour (can skip below two lines)
          x, y, w, h = cv2.boundingRect(cnt)
          cv2.rectangle(crop_img, (x, y), (x+w, y+h), (0, 0, 255), 0)
  
      # finding convex hull
          hull = cv2.convexHull(cnt)
  
      # drawing contours
          drawing = np.zeros(crop_img.shape,np.uint8)
          cv2.drawContours(drawing, [cnt], 0, (0, 255, 0), 0)
          cv2.drawContours(drawing, [hull], 0,(0, 0, 255), 0)
  
      # finding convex hull
          hull = cv2.convexHull(cnt, returnPoints=False)
  
      # finding convexity defects
          defects = cv2.convexityDefects(cnt, hull)
          count_defects = 0
          cv2.drawContours(thresh1, contours, -1, (0, 255, 0), 3)
  
      # applying Cosine Rule to find angle for all defects (between fingers)
      # with angle &gt; 90 degrees and ignore defects
          for i in range(defects.shape[0]):
              s,e,f,d = defects[i,0]
  
              start = tuple(cnt[s][0])
              end = tuple(cnt[e][0])
              far = tuple(cnt[f][0])
  
          # find length of all sides of triangle
              a = math.sqrt((end[0] - start[0])**2 + (end[1] - start[1])**2)
              b = math.sqrt((far[0] - start[0])**2 + (far[1] - start[1])**2)
              c = math.sqrt((end[0] - far[0])**2 + (end[1] - far[1])**2)
  
          # apply cosine rule here
              angle = math.acos((b**2 + c**2 - a**2)/(2*b*c)) * 57
  
          # ignore angles &gt; 90 and highlight rest with red dots
              if angle &lt;= 90:
                  count_defects += 1
                  cv2.circle(crop_img, far, 1, [0,0,255], -1)
          #dist = cv2.pointPolygonTest(cnt,far,True)
  
          # draw a line from start to end i.e. the convex points (finger tips)
          # (can skip this part)
              cv2.line(crop_img,start, end, [0,255,0], 2)
          #cv2.circle(crop_img,far,5,[0,0,255],-1)
  
      # define actions required
  
          if count_defects == 1:
              if (time.time()&gt;start_time+2):
                  if mode == "on":
                      mySocket.send("on_led1".encode())
                      state1 = "on"
                      print("led 1 is on")
                  else:
                      mySocket.send("off_led1".encode())
                      state1 = "off"
                      print("led 1 is off")
                  start_time = time.time()
              cv2.putText(img, "led 1 is "+state1, (5, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, 2)
  
  
          elif count_defects == 2:
              if (time.time()&gt;start_time+2):
                  if mode == "on":
                      mySocket.send("on_led2".encode())
                      state2 = "on"
                      print("led 2 is on")
                  else:
                      mySocket.send("off_led2".encode())
                      state2 = "off"
                      print("led 2 is off")
                  start_time = time.time()
              cv2.putText(img, "led 2 is "+state2, (5, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, 2)
  
          elif count_defects == 3:
              if (time.time()&gt;start_time+2):
                  if mode == "on":
                      mySocket.send("on_led3".encode())
                      state3 = "on"
                      print("led 3 is on")
                  else:
                      mySocket.send("off_led3".encode())
                      state3 = "off"
                      print("led 3 is off")
                  start_time = time.time()
              cv2.putText(img, "led 3 is "+state3, (5, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, 2)
          elif count_defects == 4:
              cv2.putText(img,"mode is "+mode, (50, 50), cv2.FONT_HERSHEY_SIMPLEX, 2, 2)
  
              if(time.time() &gt; start_time+2):
                  if mode == "on":
                      mode = "off"
                  else:
                      mode = "on"
                  start_time = time.time()
                  print(mode)
  
          else:
              cv2.putText(img, "use your fingure for turn On/Off lights current mode is "+mode, (5, 50), cv2.FONT_HERSHEY_SIMPLEX, 1, 2)
  
      # show appropriate images in windows
          cv2.imshow('Gesture', img)
          all_img = np.hstack((drawing, crop_img))
          cv2.imshow('Contours', all_img)
  
          k = cv2.waitKey(10)
          if k == 27:
              break
      mySocket.close()
  
  except:
  
      mySocket.send("close_all".encode())
      mySocket.close()
  </code></pre>
  
  <p>above is a program which i created for accessing embedded device using cv2 all things was working properly but still i get an error which <code>[ WARN:0] terminating async callback</code> i also use <code>camera.release()</code> <code>cv2.destroyAllWindows()</code> function but it is not work , any help would be appreciated </p>
  
  <p>i also try this suggestion<a href="https://stackoverflow.com/questions/53888878/cv2-warn0-terminating-async-callback-when-attempting-to-take-a-picture">suggestion</a> but still it is not working i am using windows 10 operating system </p>
  
  <p>here is full code with explanation <a href="https://github.com/manan5439/Automation-using-fingure-gesture" rel="nofollow noreferrer">code</a> </p>