Application hung after dialog opened during startup on macOS

[Perdrix]

My application's main contains:

		deleteRemainingTempFiles();
		mainWindow.show();

if the dialog in deleteRemainingTempFiles() is displayed on macOS, then the application is unresponsive after clicking on "Yes".
Here's what's in deleteRemainingTempFiles()

	void	deleteRemainingTempFiles()
	{
		ZFUNCTRACE_RUNTIME();
		std::vector<QString> vFiles;
		qint64	totalSize = 0;

		QString folder(CAllStackingTasks::GetTemporaryFilesFolder());

		QStringList nameFilters("DSS*.tmp");

		QDir dir(folder);
		dir.setNameFilters(nameFilters);

		for (QFileInfo item : dir.entryInfoList())
		{
			if (item.isFile())
			{
				vFiles.emplace_back(item.absoluteFilePath());
				totalSize += item.size();
			}
		}

		if (!vFiles.empty())
		{
			QString			strMsg;
			QString			strSize;

			ZTRACE_RUNTIME("Remove remaining %d temp files", vFiles.size());

			SpaceToQString(totalSize, strSize);

			strMsg = QString("One or more temporary files created by DeepSkyStacker are still in the working directory."
				"\n\nDo you want to remove them?\n\n(%1 file(s) using %2)")
				.arg(vFiles.size()).arg(strSize);

			QMessageBox msgBox(QMessageBox::Question, QString(""), strMsg, (QMessageBox::Yes | QMessageBox::No));

			msgBox.setDefaultButton(QMessageBox::Yes);

			if (QMessageBox::Yes == msgBox.exec())
			{
				QFile file;
				for (size_t i = 0; i < vFiles.size(); i++)
				{
					file.setFileName(vFiles[i]);
					file.remove();
				}
			};

		};


	};

What am I doing wrong, and what do I need to do to fix this?

Thanks, David

[Kent-Dorfman]

IIRC, ALL Qt apps have to actually start the event loop running with a call to exec().

[SGaist]

Hi,

Which version of Qt are you using ?
On which version of macOS ?

[Perdrix]

@SGaist Qt 6.10, macOS Tahoe 26.3.1.
@Kent-Dorfman AFAIK, and I could be wrong, QMessageBox::exec() runs it own local event loop.

[J.Hilk]

@Perdrix QMessageBox::exec() does run its own event loop, but your call to deleteRemainingTempFiles is after the creation of Q(Core)Application?

[Perdrix]

@J.Hilk Yes, most certainly. QCoreApplication instance is created over a 100 lines earlier.
app.exec() is called immediately after mainWindow.show().

The main window is fully displayed while that dialog is running. So it almost seems that the dlg operates asynchronously.

[Perdrix]

Hmmm Should I set that QMessageBox to be "application modal"?

[Perdrix]

Hmmm I can't recreate the problem - I was running under the debugger at the time I hit it. Perhaps that might explain it.

[Kent-Dorfman]

@Perdrix said in Application hung after dialog opened during startup on macOS:

Hmmm Should I set that QMessageBox to be "application modal"?

@Perdrix As I understand your flow, yes, the dialog should be modal since it is first and exclusive before doing mainwindow processing.