Python Serial "ClearCommError failed (OSError(9, 'The handle is invalid.', None, 6)) - python-3.x

Question

I am new to python and multiprocessing (Electronics background). I am writing an GUI application to communicate with micro controller over serial port. The interaction with user is through some buttons on the GUI, which sends some command on serial port to the MCU and displays data received from MCU in the same GUI(there can be data from MCU without any command being sent). I am using PyQt5 module and QT designer to design the UI. I converted the UI to py code using uic.compileUi. I am then calling this python file in my main code.
After reading through several documents and stack overflow posts I decided to use to QThreads for the application.
I am however facing issue with serial communication when being used inside thread (It works fine if used in a single main loop without threads).
My code is:
from PyQt5 import uic
from PyQt5.QtWidgets import QApplication,QWidget,QMainWindow #
from PyQt5.QtCore import QCoreApplication, QObject, pyqtSignal, pyqtSlot, QThread
import serial
from GUI import Ui_MainGUIWindow
import sys
serialString = ""
def ClosePort():
serialPort.close()
# print("port closed")
def OpenPort():
serialPort.open()
#print("port open")
def sendFV():
serialPort.write('fv\r'.encode())
def configSerial(port,baudRate):
global serialPort
serialPort=serial.Serial(port = port, baudrate=baudRate, bytesize=8, timeout=None, stopbits=serial.STOPBITS_ONE)
if not serialPort.isOpen():
serialPort.open()
class Worker(QObject):
finished = pyqtSignal()
dataReady = pyqtSignal(['QString'])#[int], ['Qstring']
print("workerinit")
def run(self):
print ("worker run")
while(1):
if(serialPort.in_waiting > 0):
serialString = serialPort.read()
self.dataReady.emit(str(serialString))
self.finished.emit()
class GUI(QWidget):
def __init__(self):
self.obj = Worker()
self.thread = QThread()
self.obj.dataReady.connect(self.onDataReady)
self.obj.moveToThread(self.thread)
self.obj.finished.connect(self.thread.quit)
self.thread.started.connect(self.obj.run)
self.thread.finished.connect(app.exit)
self.thread.start()
self.initUI()
def initUI(self):
#Form, Window = uic.loadUiType("TestGUI.ui")
#print(Form,Window)
#self.window = Window()
#self.form=Form()
self.window = QMainWindow()
self.form = Ui_MainGUIWindow()
self.form.setupUi(self.window)
self.form.FVButton.clicked.connect(sendFV)
print("guiinit")
self.window.show()
def onDataReady(self, serialString):
print("here")
print(serialString.decode('Ascii'))
self.form.plainTextOutput.insertPlainText((serialString.decode('Ascii')))
self.form.plainTextOutput.ensureCursorVisible()
if __name__ == '__main__':
configSerial("COM20",9600)
"""
app = QCoreApplication.instance()
if app is None:
app = QCoreApplication(sys.argv)
"""
app = QApplication(sys.argv)
form=GUI()
app.exec_()
sys.exit(ClosePort())
I get following error on line if(serialPort.in_waiting > 0):
File "C:\Users\...\Anaconda3\lib\site-packages\serial\serialwin32.py", line 259, in in_waiting
raise SerialException("ClearCommError failed ({!r})".format(ctypes.WinError()))
SerialException: ClearCommError failed (OSError(9, 'The handle is invalid.', None, 6))
I found this post talking about similar issue, but do know how exactly to implement the suggested solution in my code.
Also I get "kernel died" error multiple times when I run the code on spyder IDE. I added a check if I am creating multiple instances of QT application but that did not help.Running the code from anaconda command prompt works fine.