QMYSQL SIGSEGV

ckvsoft

Hallo

I got some failures with QMYSQL (QSQLITE will work)

My connection will be

if (dbType == "QSQLITE") {
            currentConnection = QSqlDatabase::addDatabase("QSQLITE", "CN");
            currentConnection.setDatabaseName(QString(dataDir + "/%1-%2.db").arg(date.year()).arg(basename));
        } else if (dbType == "QMYSQL") {
            QString userName = settings.value("DB_userName", "QRK").toString();
            QString password = settings.value("DB_password", "").toString();
            QString hostName = settings.value("DB_hostName", "localhost").toString();
     
            currentConnection = QSqlDatabase::addDatabase("QMYSQL", "CN");
            currentConnection.setHostName(hostName);
            currentConnection.setUserName(userName);
            currentConnection.setPassword(password);
            currentConnection.setConnectOptions("MYSQL_OPT_RECONNECT=1;MYSQL_OPT_CONNECT_TIMEOUT=86400;MYSQL_OPT_READ_TIMEOUT=60");
        }
     
        bool ok = currentConnection.open();

When i was connected and to a simple query i got, but not allways a SIGSEGV. When i remove the connection options i got "Lost connection to MySQL server during query"
no matter if MySQL Server is localhost or any Server on the Internet.

Yes, i search but found no solution. What can i do false?

OS: Linux Ubuntu (16.04 and 17.10) Server MariaDB from the Ubuntu Package

A Simply Query which returns one record and the Database holds max. 10 Entries.

    QSqlDatabase dbc = QSqlDatabase::database("CN");
        QSqlQuery query(dbc);
     
        query.prepare("SELECT strValue FROM globals WHERE name='shopName'");
        query.exec();
        query.next();
     
        name = query.value(0).toString();

thx Chris

SGaist

Hi,

What version of Qt are you using ?

ckvsoft

Hi
Oh, sorry
QT5.9.1 from Ubuntu 17.10

But also with QT5.6 on Ubuntu 16.04
lg chris

SGaist

Can you show the stack trace ?

By the way, 5.9.4 just got released, it's worth checking if it behaves better.

ckvsoft

Hi
Hope this helps ...

signal 11 (Speicherzugriffsfehler), address is 0x1b0 from 0x7fffcff1e5ea
[bt]: (1) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(+0x375ea) [0x7fffcff1e5ea]
[bt]: (2) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(+0x375ea) [0x7fffcff1e5ea]
[bt]: (3) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(+0x3865c) [0x7fffcff1f65c]
[bt]: (4) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(+0x2cbdc) [0x7fffcff13bdc]
[bt]: (5) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(+0x27516) [0x7fffcff0e516]
[bt]: (6) /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20(mysql_stmt_prepare+0x96) [0x7fffcff0e8a6]
[bt]: (7) /usr/lib/x86_64-linux-gnu/qt5/plugins/sqldrivers/libqsqlmysql.so(+0xc70c) [0x7fffd050370c]
[bt]: (8) /usr/lib/x86_64-linux-gnu/libQt5Sql.so.5(_ZN10QSqlResult11savePrepareERK7QString+0x200) [0x7ffff64260d0]
[bt]: (9) /usr/lib/x86_64-linux-gnu/libQt5Sql.so.5(_ZN9QSqlQuery7prepareERK7QString+0x208) [0x7ffff6417008]
[bt]: (10) /home/chris/Dokumente/projects/qt/build-QRK-Desktop-Debug/qrkcore/libQrkCore.so.1(_ZN8Database17getCashRegisterIdEv+0x80) [0x7ffff791f2aa]
[bt]: (11) /home/chris/Dokumente/projects/qt/build-QRK-Desktop-Debug/qrkcore/libQrkCore.so.1(_ZN14VersionChecker10getVersionEv+0x25e) [0x7ffff7992e6a]
[bt]: (12) /home/chris/Dokumente/projects/qt/build-QRK-Desktop-Debug/qrkcore/libQrkCore.so.1(_ZN9QtPrivate11FunctorCallINS_11IndexesListIJEEENS_4ListIJEEEvM14VersionCheckerFvvEE4callES7_PS5_PPv+0x7a) [0x7ffff7993e80]
[bt]: (13) /home/chris/Dokumente/projects/qt/build-QRK-Desktop-Debug/qrkcore/libQrkCore.so.1(_ZN9QtPrivate15FunctionPointerIM14VersionCheckerFvvEE4callINS_4ListIJEEEvEEvS3_PS1_PPv+0x42) [0x7ffff7993e03]
[bt]: (14) /home/chris/Dokumente/projects/qt/build-QRK-Desktop-Debug/qrkcore/libQrkCore.so.1(_ZN9QtPrivate11QSlotObjectIM14VersionCheckerFvvENS_4ListIJEEEvE4implEiPNS_15QSlotObjectBaseEP7QObjectPPvPb+0x6c) [0x7ffff7993d6d]
[bt]: (15) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN11QMetaObject8activateEP7QObjectiiPPv+0x97f) [0x7ffff5f729ff]
[bt]: (16) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN6QTimer7timeoutENS_14QPrivateSignalE+0x37) [0x7ffff5f7f3b7]
[bt]: (17) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN6QTimer10timerEventEP11QTimerEvent+0x28) [0x7ffff5f7f718]
[bt]: (18) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN7QObject5eventEP6QEvent+0x9b) [0x7ffff5f7340b]
[bt]: (19) /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(_ZN19QApplicationPrivate13notify_helperEP7QObjectP6QEvent+0x9c) [0x7ffff6f0746c]
[bt]: (20) /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5(_ZN12QApplication6notifyEP7QObjectP6QEvent+0x2a4) [0x7ffff6f0ed34]
[bt]: (21) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent+0x118) [0x7ffff5f43de8]
[bt]: (22) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN14QTimerInfoList14activateTimersEv+0x40e) [0x7ffff5f9b91e]
[bt]: (23) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0x2e20e1) [0x7ffff5f9c0e1]
[bt]: (24) /lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_dispatch+0x2e7) [0x7ffff2a69fb7]
[bt]: (25) /lib/x86_64-linux-gnu/libglib-2.0.so.0(+0x4b1f0) [0x7ffff2a6a1f0]
[bt]: (26) /lib/x86_64-linux-gnu/libglib-2.0.so.0(g_main_context_iteration+0x2c) [0x7ffff2a6a27c]
[bt]: (27) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN20QEventDispatcherGlib13processEventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE+0x5f) [0x7ffff5f9c47f]
[bt]: (28) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE+0x13a) [0x7ffff5f41e3a]
[bt]: (29) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(_ZN7QThread4execEv+0x6a) [0x7ffff5d613ca]
[bt]: (30) /usr/lib/x86_64-linux-gnu/libQt5Core.so.5(+0xac29d) [0x7ffff5d6629d]
[bt]: (31) /lib/x86_64-linux-gnu/libpthread.so.0(+0x77fc) [0x7ffff5aa27fc]
[bt]: (32) /lib/x86_64-linux-gnu/libc.so.6(clone+0x3f) [0x7ffff5232b5f]

lg Chris

JonB

@ckvsoft
At what precise point from your code does this SEGV occur? It looks like it's just in your query.prepare() statement, without even getting as far as the execute, is that what you find stepping through?

Also, why do you think you're having to specify all those timeout/reconnect options, else you say it loses connection. It shouldn't be losing connection anyway. Unless that's an artefact of an underlying problem which sometimes SEGVs and sometimes doesn't...

ckvsoft

@JonB
This was a test while without these Options i got a "Lost connection to MySQL server during query" without SEGV but the Query was not made. The Server is running normaly without troubles Its a TCP connection while not on the same machine. I test an other Server with do the same. Tomorow i will test a localhost machine.

Its not allways the same query and not allways the prepare. Sometimes it is by "QSqlQuery query(dbc)" and somtime by the exec.

SGaist

What is that qrkcore library you are using ?

ckvsoft

@SGaist
This is a Part of my Application . Why?

SGaist

Well... To know whether it's an external library you are using or something you are implementing.

Do you have the same crash if you implement just a minimal application that connects to the database and does the queries ?

ckvsoft

@SGaist
I will try this at weekend. Also i will test if MySQL and MariaDB has the same. The queries where made from the library. Thx for the time

ckvsoft

Hi
I connect to a localhost mysql server and it ~~seems to work~~. When i has running in the background some sql queries and i do at the same time from other window with the same connection any query ~~it works.~~

When i connect to a server via TCP it will crash.
Edit: Its also with localhost, but the time is a bit longer ;(

SGaist

Can you trigger also that when using an application that's not using the QSql** classes ?

ckvsoft

I think i have found a solution ;-) Some Test will be good. I will enhance my tests.
The Idea i found by reading http://doc.qt.io/qt-5/threads-modules.html

Just my Application worked since 2015 with QSQLITE without troubles. But some users will also use MySQL.

For the solution i have adapted a database manager for my requirement.

SGaist

So you're using multiple threads to write to your database ?

ckvsoft

@SGaist
Yes. I Import JSON Files with an Import Walter Thread. Wenn a File is copied in a Directory it will Import and created new sql entries.
Nur Why SQlite has no Troubles?
I will also Move long Working Stuff to thread

Ob they GUI you also can do some queries by clicking Buttons

SGaist

I'd say pure luck.

Are you creating one connection per thread like suggested in the documentation ?

ckvsoft

@SGaist
Yes. The DatabaseManager save the connections per thread into a

QHash<QThread*, QHash<QString, QSqlDatabase> >

I have only one thread at a time wich write to the database. All others max. 4 to only select
Sorry for my "Austrian English" ;-)

SGaist

Can you show how your are setting up the connections ?

ckvsoft

@SGaist

The first connection is in my first post
Than for every connection i call

QSqlDatabase dbc = DatabaseManager::database("CN");
QSqlQuery query(dbc)
.
.

.

#include "databasemanager.h"

#include <QSqlDatabase>
#include <QMutexLocker>
#include <QThread>
#include <QSqlError>
#include <QDebug>

QMutex DatabaseManager::s_databaseMutex;
QHash<QThread*, QHash<QString, QSqlDatabase> > DatabaseManager::s_instances;

QSqlDatabase DatabaseManager::database(const QString& connectionName)
{
    QMutexLocker locker(&s_databaseMutex);
    QThread *thread = QThread::currentThread();

    // if we have a connection for this thread, return it
    QHash<QThread*, QHash<QString, QSqlDatabase> >::Iterator it_thread = s_instances.find(thread);
    if (it_thread != s_instances.end()) {
        QHash<QString, QSqlDatabase>::iterator it_conn = it_thread.value().find(connectionName);
        if (it_conn != it_thread.value().end()) {
            QSqlDatabase connection = it_conn.value();
//            qDebug() << "Function Name: " << Q_FUNC_INFO << " found SQL connection instances Thread: " << thread->currentThreadId() << " Name: " << connectionName;
            if (connection.isValid())
                return it_conn.value();
        }
    }

    // otherwise, create a new connection for this thread
    QSqlDatabase connection = QSqlDatabase::cloneDatabase(
                                  QSqlDatabase::database(connectionName),
                                  QString("%1_%2").arg(connectionName).arg((int)thread));

    // open the database connection
    // initialize the database connection
    if (!connection.open()) {
        // Todo: Exeption Handling
        qCritical() << "Function Name: " << Q_FUNC_INFO << connection.lastError().text();
        return connection;
    }

    qDebug() << "Function Name: " << Q_FUNC_INFO << " new SQL connection instances Thread: " << thread->currentThreadId() << " Name: " << connectionName;

    s_instances[thread][connectionName] = connection;
    return connection;
}

#ifndef DATABASEMANAGER_H
#define DATABASEMANAGER_H

#include "qrkcore_global.h"

#include <QMutex>
#include <QHash>
#include <QSqlDatabase>

class QThread;

class QRK_EXPORT DatabaseManager
{
    public:
        static QSqlDatabase database(const QString& connectionName = QLatin1String(QSqlDatabase::defaultConnection));
    private:
        static QMutex s_databaseMutex;
        static QHash<QThread*, QHash<QString, QSqlDatabase>> s_instances;

};

#endif // DATABASEMANAGER_H

I found the code and adapted it for my requirement.

Solved QMYSQL SIGSEGV