Starting/stopping function using QT GUI buttons - c++

Question

I am writing a simple Qt C++ GUI window for the user to input certain values for a USRP device to record (i.e. input start frequency, stop frequency, etc..). Once the user inputted the values, the "EXECUTE" button is clicked and the execute_run_usrp() function is called in its own thread (so not to block the GUI). Then the STOP button should be able to be clicked at any time to terminate the thread running the function that runs the USRP, execute_run_usrp(), thus terminating the USRP recording process.
The function run_usrp(x,y,z,etc) is defined in another *.cpp file in the Project.
The problem that I am having that the STOP button when clicked only seems to "pause" the function...doesn't actually kill it (like with CTRL-C, which works great here)
Here is my code from MainWindow.cpp for the EXECUTE button click:
// run the following when EXECUTE button is clicked
void MainWindow::on_button_EXECUTE_clicked()
{
if ( ui->calculated_StartTime->text() == "" )
{
QMessageBox messageBox;
messageBox.critical(0,"Error","Hit the \"CALCULATE SCHEDULE\" button first above!!");
messageBox.setFixedSize(500,200);
return;
}
ui->button_STOP->setVisible(true);
ui->button_EXECUTE->setVisible(false);
auto function = std::bind([this]{execute_run_usrp();});
QThread* temp = QThread::create(function);
temp->start();
connect( ui->button_STOP, SIGNAL(clicked()), temp, SLOT( terminate() ));
}
Here is the execute_run_usrp() function:
void MainWindow::execute_run_usrp()
{
float startFreq = ui->input_startFreq->text().toFloat();
float stopFreq = ui->input_stopFreq->text().toFloat();
float stepFreq = ui->input_stepFreq->text().toFloat();
int nRepeats = ui->input_numRepeats->text().toInt();
float ipp = ui->input_IPP->text().toFloat();
int sweepCadence = ui->calculated_sweepCadence->text().toInt();
int numSweeps = ui->input_numSweeps->text().toInt();
std::string schedule_run = ui->calculated_StartTime->text().toStdString();
std::cout << startFreq << std::endl;
std::cout << stopFreq << std::endl;
std::cout << stepFreq<< std::endl;
std::cout << nRepeats << std::endl;
std::cout << ipp << std::endl;
std::cout << sweepCadence << std::endl;
std::cout << numSweeps << std::endl;
run_usrp(startFreq, stopFreq, stepFreq, nRepeats, ipp, sweepCadence, numSweeps, schedule_run);
}
And here is the STOP button code:
void MainWindow::on_button_STOP_clicked()
{
ui->button_STOP->setVisible(false);
ui->button_EXECUTE->setVisible(true);
}
Clicking the STOP button only seems to pause the function, doesn't actually kill it like doing CTRL-C with the keyboard. I think the UHD library (that runs the USRPs) spwans its own thread for running.
Question: How do I 100% terminate the entire function (and including any spwaned children from UHD) when I hit the STOP button ?
Thank you very much!

Answer 1

How do I 100% terminate the entire function (and including any spwaned children from UHD) when I hit the STOP button ?
From the code you've shown there's no easy answer imho.
The shortest one is: by incorporating some inter-thread communication inside the USRP function, provided you want some sort of graceful exit.
As for terminate, QT's docs state:
This function is dangerous and its use is discouraged. The thread can be terminated at any point in its code path. Threads can be terminated while modifying data. There is no chance for the thread to clean up after itself, unlock any held mutexes, etc. In short, use this function only if absolutely necessary.
Alternatively, the whole USRP function can be run inside a separate process, that is then killed. Again, plain killing of the process is far from graceful, still it seems easier and safer than doing it to a thread. You may want to check QProcess for reference.