QThread(C++) and QTimer failed to call Python

whuw

goal: QThread(C++) child threads call deep learning Python training code, and display the training result (PyObject) on the Qt GUI in the main thread.

problem: the main thread displays training results in real time, using QTimer, which convert PyObject objects to C++ variables every 1 second. QTimer periodically accesses variables in PyObject, which will cause access conflicts when child threads call Python modules. The main thread calls the following code in real time:

//Main thread real-time display function

void DeepLearning::trainVis()
{
    class PyThreadStateLock PyThreadLock; //Get Python GIL

    dictGuinfoRealtime = trainThread.dictGuinfoRealtime; //Passes the real-time results of the child thread to the main thread variable

    //elapsed_runtime

    //An attempt to access variables in dictGuinfoRealtime will result in an access conflict when the child thread calls the Python module
    PyObject* elapsedruntime_ = PyDict_GetItemString(dictGuinfoRealtime, "elapsed_runtime");
    Py_XDECREF(elapsedruntime_);

}

The child thread calls the Python training module as follows:

```C++
//The child thread calls Python training code

class PyThreadStateLock PyThreadLock; //Get Python GIL

PyObject* pTrainS = PyImport_ImportModule("train");//"Train" is the file name of the training file 'train.py'

PyObject* args = PyTuple_New(1);
PyObject* TrainFun = PyObject_GetAttrString(pTrainSeg, "main");
if (TrainFun && PyCallable_Check(TrainFun))
{
	PyTuple_SetItem(args, 0, dictGuinfoRealtime);

	if (!PyObject_CallObject(TrainFun, args)) //Access conflicts are reported here during training
	{
		throw std::exception("PyObject_CallObject failed!");
	}	
}
Py_XDECREF(TrainFun);
```

Struggled for a long time still did not find a solution, please give some advice, thank you!

SGaist

Hi and welcome to devnet,

Since your main code is in Python, why not use PySide6 for your GUI ? So you can stay with the same language.

whuw

@SGaist Thanks for your advice! This is because of requirements, the GUI interface must use C++

SGaist

Ok, one thing that is not clear with your code explanation: why does the gui poll the algorithm execution every second for results ? Shouldn't the object handling that execution notify the other elements of the application once they are done ?