QThread - changing data in global list - different values - locking

Question

I am using QThread to do some time intensive calculations to keep GUI from freezing. In the QThread I am accessing and changing global lists many times during the thread life span, however I am unable to get the same result as if it were just on the main thread.
I would assume you had to perform some kind of lock, but i'm new to QThread and don't know how to implement it.
#Main Thread
self.runGasAnalysisThread = GasAnalysisThread()
self.runGasAnalysisThread.start()
#QThread
class GasAnalysisThread(QtCore.QThread):
"""Performs gas analysis function"""
def __init__(self,parent = None):
super().__init__(parent)
def run(self):
try:
boolValue = True
while True:
#Change lists here
float(Data.TestList[0])+ 1 #Data is another module I am using to store variables
Again, moving the code to the main thread works correctly, but as soon as I do it with QThread I get different results.
How would I implement a locking mechanism to keep this from happening?

Answer 1

It is common to be confused while using Qt's threading, as one would think that subclassing QThread would be the right path.
Truth is that a QThread is the Qt thread object where your process is actually run, which means that you'll need a separate class for it and move its instance in a QThread. Subclassing QThread is usually unnecessary.
If you need any kind of interaction between the "worker" (the object that does the processing) and the main thread (as in the GUI), it's good practice to use Qt's signals.
In this example I'm using a button to start the processing, once the processor is started it disables the button, and re-enables it once it signals that the process has finished.
class Worker(QtCore.QObject):
stateChanged = QtCore.pyqtSignal(bool)
def __init__(self):
super().__init__()
def run(self):
self.stateChanged.emit(True)
try:
boolValue = True
while True:
# this doesn't make much sense, as it doesn't seem to do anything;
# I'll leave it just for the sake of the argument
float(Data.TestList[0]) + 1
except:
pass
self.stateChanged.emit(False)
class SomeWidget(QtWidgets.QWidget):
def __init__(self, parent=None):
super().__init__(parent)
layout = QtWidgets.QHBoxLayout()
self.setLayout(layout)
self.startButton = QtWidgets.QPushButton('Start')
layout.addWidget(self.startButton)
self.worker = Worker()
self.workerThread = QtCore.QThread()
self.worker.moveToThread(self.workerThread)
self.workerThread.started.connect(self.worker.run)
self.startButton.clicked.connect(self.workerThread.start)
self.worker.stateChanged.connect(self.startButton.setDisabled)