title: Flask app should not exit when I use os.killpg
body: <p>I have a flask app with 3 functions, one of the function is in a subprocess, and I am killing that subprocess using os.killpg, but when the program executes os.killpg, the command is terminating the flask app itself. I want to just terminate the subprocess, not flask app.
  Can you please help with this?</p>
  
  <pre><code>flask import Flask, Response, request, jsonify
  import subprocess
  import time
  import os
  import signal
  
  app = Flask(__name__)
  
  @app.route("/cam", methods=['POST'])
  def cam():
  
      cmd3 = "gst-launch-1.0 -v v4l2src ! video/x-raw,format=YUY2 ! 
                    videoconvert ! autovideosink"
      process3 = subprocess.Popen(cmd3, shell = True)
      time.sleep(1)
      os.killpg(os.getpgid(process3.pid), signal.SIGTERM)
  
  @app.route("/one", methods=['POST'])
  def one():
      " some commands
      "
  
  @app.route("/two", methods=['POST'])
  def two():
      " some commands
      "
  
  if __name__ == "__main__":
  
      app.run(debug=True, host='0.0.0.0', port = 6005)
  </code></pre>