QSqlDatabase - memory leak

Tancen

qt 5.7 mingw 32bits

#include <qcoreapplication.h>
#include <QSqlDatabase>
#include <qdebug.h>
#include <quuid.h>
#include <qsqldatabase.h>
#include <qsqlquery.h>

bool gExit = false;

void handleSignal(int sig)
{
    gExit = true;
}

void test1()
{
    QString name = QUuid::createUuid().toString();
    QSqlDatabase *db = new QSqlDatabase(QSqlDatabase::addDatabase("QOCI", name));
    db->setDatabaseName("test");
    db->setHostName("localhost");
    db->setPort(1521);
    db->setUserName("system");
    db->setPassword("123456");

    for (int i = 0; i < 1000; ++i)
    {
        if(!db->open())
        {
            qDebug("db->open failed");
            delete db;
            return;
        }

        db->close();
        qDebug("done %d", i);
    }
    delete db;
    //QSqlDatabase::removeDatabase(name); //unless enable this
}

int main(int argc, char *argv[])
{
    signal(SIGINT, handleSignal);
    QCoreApplication app(argc, argv);

    test1();

    int ret = app.exec();
    return ret;
}

memory malloc in db.open, but not free in db.close.

jsulm

@Tancen It would be nice to describe the problem instead simply throwing some code...
You don't delete db if you do a return in

if(!db->open())
{
    qDebug("db->open failed");
    return;
}

Why do you create db on the stack?

QSqlDatabase db;

would be enough.

Tancen

i forget it. but the problem is not about it. you can try and repeat open / close more times.

Taz742

@Tancen

@Tancen said in QSqlDatabase - memory leak:

you can try and repeat open / close more times.

He knows it.

It tells you that if the base is not opened, you're doing 'return' and this is exactly the problem, 'return' - has finished function and the base itself will not be removed.

    for (int i = 0; i < 1000; ++i)
    {
        if(!db->open())
        {
            qDebug("db->open failed");
            delete db;
            return; //stop function
        }

        db->close();
        qDebug("done %d", i);
    }
    delete db; //It will not be fulfilled.

Tancen

thanks.
i know he means.
i tested and get memory leak about open/close
my code is only a mini show

jsulm

@Tancen How do you know you have a memory leak?

Tancen

i repeat the for 1000 times, i see the memory increase in windows task manager and not decrease on the for finished

SGaist

Hi,

No OS guaranties that when you call delete, the memory is returned instantly to said OS. All the more if you are using a tight loop like that.

Note that you are also not using the QSqlDatabase API correctly.

Tancen

it's same as wait it some time.
i tested the memory free at QSqlDatabase::removeDatabase be called