Sharing Data Between Main Window and Thread in PyQt

Multithreaded applications often need to share data between the main window thread and worker threads. To ensure thread-safety and proper communication, PyQt offers several practical approaches.

Option 1: Direct Reference to Main Window

In this approach, a reference to the main window is passed to the thread. The thread can then directly access the data in the main window, such as the value of a spinbox.

class MainWindow(QtGui.QWidget):
    def __init__(self):
        # ...
        self.worker = Worker(self)
        # ...

class Worker(QtCore.QThread):
    def __init__(self, host_window):
        super(Worker, self).__init__()
        self.host = host_window
        # ...

Option 2: Signals and Slots

PyQt uses signals and slots to communicate between objects. In this approach, the worker thread emits signals when data changes, and the main window slot functions handle the updates.

class MainWindow(QtGui.QWidget):
    def __init__(self):
        # ...
        self.worker = Worker()
        self.worker.beep.connect(self.update)
        # ...

class Worker(QtCore.QThread):
    beep = QtCore.pyqtSignal(int)

    def __init__(self):
        super(Worker, self).__init__()
        # ...

Which Option to Use?

The choice depends on the thread's needs and the level of control required.

• Option 1 offers direct access to main window data but may not be as scalable for more complex data sharing.
• Option 2 ensures thread-safety and supports more flexible communication patterns.

Thread Safety Considerations

Widgets are not thread-safe. Therefore, it is crucial to use signals and slots to handle communication between the thread and the main window. Direct manipulation of widgets from multiple threads can lead to unexpected behavior.