Function QDateTime::toString(const QString& format) is not reentrant

#include <QCoreApplication>
#include <thread>
#include <QDateTime>

void func()
{
	QDateTime dt = QDateTime::currentDateTimeUtc();
	for (int i = 0; i < 1000000; i++)
		QString s = dt.toString(QStringLiteral("hh:mm:ss.zzz"));
}

int main(int argc, char *argv[])
{
	QCoreApplication a(argc, argv);

	std::thread t1(func);
	std::thread t2(func);
	std::thread t3(func);

	t1.join();
	t2.join();
	t3.join();

	return a.exec();
}