Logging messages: qlogging.h

[sitesv]

Hi!
Sometimes after the start program, I have an "ASSERT: bytes <= bufferSize in file tools qringbuffer.cpp line 113". I supposed that this is caused because of using qlogging mechanism in the multithread app.

There is a messageHandler. Should I sync any qLog executions?

Thank you.

[SGaist]

Hi,

Do you have a custom message handler ?

[sitesv]

@SGaist I don’t know.

void messageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg);
...
void main(...)
{
qInstallMessageHandler(messageHandler);
}

[SGaist]

Well, installing a custom message handler usually means to you are using a custom message handler.

You have to handle the threading aspect in your custom handler.

[sitesv]

@SGaist , so, This messageHandler handles various types of log messages. So, I think this is a custom messages handler. Tomorrow I will post a code of handler.

[sitesv]

@SGaist said in Logging messages: qlogging.h:

You have to handle the threading aspect in your custom handler

What do you mean?

[SGaist]

@sitesv said in Logging messages: qlogging.h:

@SGaist , so, This messageHandler handles various types of log messages. So, I think this is a custom messages handler. Tomorrow I will post a code of handler.

Calling qInstallMessageHandler implies that you are using a custom message handler.

@sitesv said in Logging messages: qlogging.h:

@SGaist said in Logging messages: qlogging.h:

You have to handle the threading aspect in your custom handler

What do you mean?

That you have to use proper threading primitives to protect the resources you access in your handler.

[sitesv]

@SGaist there is a handler code:

// Handler
void messageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
    // Creating writing-stream
    QTextStream out(m_logFile.data());
    // Adding data/time
    out << QDateTime::currentDateTime().toString("yyyy-MM-dd hh:mm:ss.zzz ");
    // Detecting message type
    switch (type){
        case QtInfoMsg:     out << "INF "; break;
        case QtDebugMsg:    out << "DBG "; break;
        case QtWarningMsg:  out << "WRN "; break;
        case QtCriticalMsg: out << "CRT "; break;
        case QtFatalMsg:    out << "FTL "; break;
    }
    // Adding message type and message
    out << context.category << ": " << msg << endl;
    out.flush();
}

There are no external resources... Only message as handler parameter.

[Christian Ehrlicher]

@sitesv Please read the answer from @SGaist :

That you have to use proper threading primitives to protect the resources you access in your handler.

So make sure your message handle can not be called from two threads simultaneously with e.g. a mutex.

[JonB]

@Christian-Ehrlicher , @SGaist
I have a quick question here: does Qt have any restriction on which threads can execute a QFile::method(), compared to the thread where the QFile m_logFile was created? Like, I know you can only do QSql... operations in the thread which created the database connection, does that apply to QFile, or are you free to write to that from any thread??

[Christian Ehrlicher]

No, as long as you add a proper mutex.