Meaning of Process finished with exit code -1073740791 (0xC0000409) code example

Example: Process finished with exit code -1073740791 (0xC0000409)

class serialThreadC(QThread):
    updateOutBox = QtCore.pyqtSignal(str)
    updateStatus = QtCore.pyqtSignal(int)

    def __init__(self):
        super(serialThreadC, self).__init__()
        self.ser = False
        self.state = 0
        self._mutex = QMutex()
        self.serialEnabled = False   

    def ConnDisconn(self):
        self._mutex.lock()
        self.serialEnabled = not self.serialEnabled
        self._mutex.unlock()

    def run(self):
        while True:
            if self.state == -3 or self.state == -2:
                self._mutex.lock()
                if self.serialEnabled:
                    self.updatePB(20)
                self._mutex.unlock()
            elif self.state == 0:
                self._mutex.lock()
                if self.serialEnabled:
                    self.updatePB(20)
                self._mutex.unlock()