QThread: Destroyed while thread is still running and QMutex destroyed - c++

Question

I am trying to add multiple threads to my Qt application but right when it executes this thread the program just crashes and i get an error of
QThread: Destroyed while thread is still running
QMutex: destroying locked mutex
I understand the error message i just dont know how i can fix it. My code is below.
Header
class Worker : public QObject
{
Q_OBJECT
private slots:
void onTimeout()
{
qDebug()<<"Worker::onTimeout get called from?: "<<QThread::currentThreadId();
}
};
class Thread : public QThread
{
Q_OBJECT
private:
void run()
{
qDebug()<<"From work thread: "<<currentThreadId();
QTimer timer;
Worker worker;
connect(&timer, SIGNAL(timeout()), &worker, SLOT(onTimeout()));
timer.start(1000);
exec();
}
};
login.cpp
void Login::on_pushButton_clicked()
{
QSqlQuery query;
QString Username = ui->Username_lineEdit->text();
QString Password = ui->Password_lineEdit->text();
query.prepare("SELECT * FROM Program_account WHERE Login = '"+ Username +"' AND Password = '"+ Password +"'");
if(!query.exec())
{
qDebug() << "SQL QUERY Login:" << query.executedQuery();
qDebug() << "SQL ERROR Login:" << query.lastError();
}
else if(!query.first())
{
tries++;
int x = 10 - tries;
ui->label->setText("Incorrect Username or Password " + QString::number(x) + " tries until timeout");
}
else
{
QSqlQuery Account_Type_Query("SELECT Account_Type FROM Program_account WHERE Login = '"+ Username +"' AND Password = '"+ Password +"'");
while(Account_Type_Query.next())
{
Account_Type = Account_Type_Query.value(0).toInt();
}
tries = 0;
static Home *home = new Home;
home->show();
close();
}
if(tries == 10)
{
Thread t;
t.start();
ui->label->setText("Password entered wrong too many times, entered 10 minute cooldown period");
ui->pushButton->hide();
QTimer::singleShot(600000, ui->pushButton, SLOT(show()));
tries = 0;
ui->label->setText("");
}
What is the correct way i can fix this issue. All help is much appreciated.
Thank you
Update:
Tried
class Thread : public QThread
{
Q_OBJECT
private:
void run()
{
while(QThread::wait())
{
qDebug()<<"From work thread: "<<currentThreadId();
QTimer timer;
Worker worker;
connect(&timer, SIGNAL(timeout()), &worker, SLOT(onTimeout()));
timer.start(1000);
exec();
}
QThread::quit();
}
};
but still receiving the same error

Answer 1

Inheriting from QThread is one issue here and I suspect that the Worker object does not have the thread affinity you think it has and is running on the main thread.
The reason for the crash is that you create your Thread instance on the stack,
if(tries == 10)
{
Thread t; // NOTE THIS IS ON THE STACK
t.start();
ui->label->setText("Password entered wrong too many times, entered 10 minute cooldown period");
ui->pushButton->hide();
QTimer::singleShot(600000, ui->pushButton, SLOT(show()));
tries = 0;
ui->label->setText("");
}
The Thread instance is being destroyed when it goes out of scope.
Regardless, I strongly suggest following the advice of #Thomas and adhere to the way in which Maya uses threads, without the need for inheriting QThread.