Question

For example:

class DemoFrame(wx.Frame):

    def __init__(self):
        Initializing
        ...
        self.TextA = wx.StaticText(MainPanel, id = -1, label = "TextAOrWhatever")
        self.TextB = wx.StaticText(MainPanel, id = -1, label = "TextBOrWhatever")
        ...

    def StaticTextUpdating(self, ObjectName, Message):
        ObjectName.SetLabel(Message)

    def WorkerA(self):
        while True:
            Work on something

            UpdatingThread = threading.Thread(target = self.StaticTextUpdating, args = (self.TextA, "Something for TextA", ))
            UpdatingThread.start()

            time.sleep(randomSecs)

    def WorkerB(self):
        while True:
            Work on something

            UpdatingThread = threading.Thread(target = self.StaticTextUpdating, args = (self.TextB, "Something for TextB", ))
            UpdatingThread.start()

            time.sleep(randomSecs)

    ...

    def StartWorking(self):
        Spawn WorkerA thread
        Spawn WorkerB thread
        ...

As you can see, I always update StaticText in new threads, and I’m 100% sure at a whatever certain time point there’s only one thread updating a specific object, but the problem is, every now and then after running for a while, some objects just disappear. Why is this happening? Does it mean GUI updating is not thread safe? Maybe only one object can be updated at a certain time point?

Added:

OK, wx.CallAfter should be a good solution for above codes. But I got another question, what if a button event and SetLabel happens at the same time? Wouldn’t things like this cause troubles although I don’t see any?

Answer 1

Most wx methods are not thread-safe. Use wx.CallAfter if you want to invoke a wx method from another thread; replace

ObjectName.SetLabel(Message)

with:

wx.CallAfter(ObjectName.SetLabel, Message)

Edit: Some Background Information

In wx (And in most other UI platforms) all the UI updates get executed in a single thread called main thread (Or UI Thread). This is to make the UI work faster by avoiding the performance hit of thread synchronization.

But the down side of this is that If we write code to update the UI from a different thread the results are undefined. Sometimes it may work, sometimes it may crash, sometimes some other thing may happen. So we should always go to UI thread to do the UI updates. So we use CallAfter function to make UI update function execute in the UI thread.

UI thread in java

UI thread in C#