Timer with Lambda function

SPlatten · 16 Dec 2020, 09:06

@KroMignon , I'm impatient, I know there is benefit from reading the documentation, I just don't want to stop what I'm doing to spend what would seem a long time to digest the documentation.

KroMignon · wrote on 16 Dec 2020, 09:06

@SPlatten said in Timer with Lambda function:

I'm impatient,

Perhaps you are impatient, but in fact you are losing days doing nonsense code which not working.
If that is the best way to work, I am pretty sure NO.

Reading this document would take you 1 or 2 hours, how many hours have you spend to create those non working code?

jsulm · wrote on 16 Dec 2020, 09:10

@SPlatten said in Timer with Lambda function:

I just don't want to stop what I'm doing to spend what would seem a long time to digest the documentation

So, instead you waste your time here?
I really don't get the logic...

SPlatten · 16 Dec 2020, 09:19

The logic is I was I was hoping this would be quicker...obviously wrong, no worries, I will read the documentation.

KroMignon · 16 Dec 2020, 09:26

@SPlatten said in Timer with Lambda function:

The logic is I was I was hoping this would be quicker...obviously wrong, no worries, I will read the documentation.

The point is not to read all Qt documentation, but at least the basics to understand how Qt is working.
There are very basic notion to know.
This will help you to right build your software and to take advantage of Qt architecture.

And, as Qt is a asynchronous framework, most of the time you don't have to create threads.
One thing is very important, never look thread this also locks the QEventLoop and break major Qt feature ==> signals/slots handling.

SPlatten · 16 Dec 2020, 09:31

@KroMignon , thanks for the advice, I've modified the thread loop to:

void clsMsgSender::run() {    
    QJsonObject objJSON;
    while( blnAnythingToDo(objJSON) == true ) {
    //Sleep to allow a small cap between transmission
        exec();
        QThread::usleep(100);
    //Look for a module name in the message
        QJsonObject::iterator itrFound = objJSON.find(clsJSON::mscszMsgType);

        if ( itrFound != objJSON.end() ) {
            const QJsonValueRef crobjMsgType = itrFound.value();
            QString strMsgType(crobjMsgType.toString());

            if ( strMsgType.compare(clsJSON::mscszAck) != 0 ) {
    //Insert a unique message ID into the message
                objJSON.insert(clsJSON::mscszMsgID, QString::number(++clsMsgSender::msulnglngMsgID));
    //Create entry to monitor status of this message
                new clsMsgTrkr(this, objJSON);
            }
        }
    //Writes message to socket
        emit write(objJSON);
    }
    emit queueEmpty();
}

I've also added a class to replace the original structure:

    class clsMsgTrkr {
    Q_OBJECT

    private:
        static const quint16 mscuint16AckTimeout = 5000;
        static mmpAck msmpAcks;

        QJsonObject mobjMsg;
        clsMsgSender* mpMsgSndr;
        QTimer mtmrMonitor;

    public:
        clsMsgTrkr(clsMsgSender* pMsgSndr, QJsonObject& robjJSON);
        ~clsMsgTrkr();

    signals:
        void startTiming();

    public slots:
        void onStartTiming();
        void onTimeout();
    };

The implementation:

//Static initialisation
mmpAck clsMsgTrkr::msmpAcks;
/**
 * @brief clsMsgTrkr - Class constructor
 * @param pMsgSndr : Pointer to message sending class
 * @param robjJSON : Reference to JSON message
 */
clsMsgTrkr::clsMsgTrkr(clsMsgSender* pMsgSndr, QJsonObject& robjJSON) {
    mobjMsg = robjJSON;
    mpMsgSndr = pMsgSndr;
//Add tracker to list
    clsMsgTrkr::msmpAcks.insert(std::make_pair(clsMsgSender::ulnglngGetMsgID(), this));
}
/**
 * @brief clsMsgTrkr::~clsMsgTrkr - Class desctructor
 */
clsMsgTrkr::~clsMsgTrkr() {
    if ( mtmrMonitor.isActive() ) {
        mtmrMonitor.stop();
    }
}
/**
 * @brief clsMsgTrker::onStartTiming
 */
void clsMsgTrkr::onStartTiming() {
    QObject::connect(&mtmrMonitor, &QTimer::timeout, this, &clsMsgTrkr::onTimeout);
    mtmrMonitor.start(1);//mscuint16AckTimeout);
}
/**
 * @brief clsMsgTrkr::onTimeout
 */
void clsMsgTrkr::onTimeout() {
    qdbg() << "TIMEOUT!";
    //Re-send message
    emit mpMsgSndr->write(mobjMsg);
}

Its still a work in progress, but I'm struggling with the compile errors:

../clsMsgSender.cpp:242:14: note: in instantiation of function template specialization 'QObject::connect<void (QTimer::*)(QTimer::QPrivateSignal), void (clsMsgTrkr::*)()>' requested here
    QObject::connect(&mtmrMonitor, &QTimer::timeout, this, &clsMsgTrkr::onTimeout);

JonB · wrote on 16 Dec 2020, 09:31

@SPlatten
If I'm not mistaken, you have not pasted the line before (or maybe after) the one you quote, which says what the actual error is.....

KroMignon · 16 Dec 2020, 09:45

@SPlatten said in Timer with Lambda function:

class clsMsgTrkr {
Q_OBJECT

Does not made sense, do you mean?

class clsMsgTrkr : public QObject 
{
     Q_OBJECT
...
};

SPlatten · 16 Dec 2020, 09:56

@KroMignon thank you, that was the problem I originally based the class on QTimer.

KroMignon · 16 Dec 2020, 09:58

@SPlatten said in Timer with Lambda function:

thank you, that was the problem I originally based the class on QTimer.

Sorry, but that is only one of your problems.
I know, each developer has his own programming style, but you are very confusing.

You are mixing to many things and subclassing Qt classes which does not really required to be (like QTimer and QThread).

And calling exec() in the run() slot will of course start the QEventLoop. But, all code after exec() will be executed on QEventLoop end!.

There are so many errors, I don't know where to start.
Sorry but please read this to understand how to use threads with Qt:

SPlatten · wrote on 16 Dec 2020, 09:58

@KroMignon , ok thank you.

SPlatten · 16 Dec 2020, 17:03

@KroMignon , I've just been reading the links that you posted.

The first link is interesting in the it states: "Right because QThreads are in fact quite easy to use, as long as you ignore the incorrect official Qt documentation on QThread"

I've been modifying some of my threads based on this information. The second link shows illustrations Usage 1-1 which is identical to the way I've implemented a class derived from QThread that does not call exec in the run function.

I'm still reading and working through the documentation.

KroMignon · 16 Dec 2020, 17:12

@SPlatten said in Timer with Lambda function:

I'm still reading and working through the documentation.

Great to see that you are starting reading documentation.

What you should learn is that subclassing QThread (or QTimer) is in 99.9% case a nonsense, there are absolut no benefit.
It is even more easy to create a worker class and move the instance to the dedicated thread.

One reason is that QThread is a QObject which is holding a thread. So the QThread signals/slots are "living" in the thread in which the QThread instance has been created. But the QObject which are moved to the QThread instance are living in the holded thread.

Another reason is that you could use the worker in current thread or in a dedicated thread without having to do any change.

Try to think simple, things becomes complex quickly enough!

SPlatten · 16 Dec 2020, 18:16

@KroMignon said in Timer with Lambda function:

QThread

Here is my new implementation of my debugging thread:

if ( clsDebugService::mspThread == nullptr ) {
        clsDebugService::mspThread = new QThread;
        moveToThread(clsDebugService::mspThread);
        //connect(this, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
        connect(clsDebugService::mspThread, SIGNAL(started()), this, SLOT(process()));
        //connect(this, SIGNAL(finished()), clsDebugService::mspThread, SLOT(quit()));
        connect(this, SIGNAL(finished()), this, SLOT(cleanup()));
        clsDebugService::mspThread->start();
}

mspThread is a static member of the class clsDebugService, clsDebugService is derived from QObject.

The cleanup slot:

void clsDebugService::cleanup() {
    if ( clsDebugService::mspThread != nullptr ) {
        if ( clsDebugService::mspThread->isFinished() != true ) {
            clsDebugService::mspThread->quit();
        }
        delete clsDebugService::mspThread;
        clsDebugService::mspThread = nullptr;
    }
}

The process slot:

void clsDebugService::process() {
    QString strData, strPath(clsDebugService::strGetUserFolder());
    clsDebugService* pService = clsDebugService::pGetService();

    while ( pService != nullptr ) {
        {
    //Anything on the stack?
            QMutexLocker lock(&pService->mMutex);

            if ( pService->mStack.size() == 0 ) {
    //Nothing on the stack, terminate thread
                break;
            }
            strData = pService->mStack.pop();
        }
        if ( strData.isEmpty() == true ) {
            continue;
        }
        QStringList slstLines = strData.split("\n");
        strData = "";
    //+2 to allow for type prefix and colon
        QString strPadding(" ");
        strPadding = strPadding.repeated(clsDebugService::mscintSeqNoLength + 2);
        uint16_t uint16Line = 1;
        foreach( QString strLine, slstLines ) {
            if ( uint16Line++ > 1 ) {
    //Insert padding at the front of additional lines
                strLine = strPadding + strLine;
            }
            bool blnToFile;
            if ( pService->blnToFile(blnToFile) == true && blnToFile == true ) {
                bool blnAutoFileName, blnOpen;
                if ( pService->blnAutoFileName(blnAutoFileName) != true ) {
                    blnAutoFileName = false;
                }
                if ( blnAutoFileName == true ) {
                    QChar qcPadding('0'), qcSeperator(QDir::separator());
                    QDate dtNow(QDate::currentDate());
                    int intBase(10), intYear(dtNow.year()), intMonth(dtNow.month()), intDay(dtNow.day());
    //Generate file name using year, month, day
                    QString strExisting, strFileName = QString("%1%2%3%4").arg(mstrPrefix)
                                                            .arg(intYear, 4, intBase, qcPadding)
                                                            .arg(intMonth, 2, intBase, qcPadding)
                                                            .arg(intDay, 2, intBase, qcPadding);
                    pService->blnFileName(strExisting);

    //Is file open and is the size greater than the limit?
                    qint64 int64FileSize;

                    if ( pService->blnIsFileOpen(blnOpen) == true
                      && blnOpen == true
                      && pService->blnFileSize(int64FileSize) == true
                      && int64FileSize > pService->mcint64FileSizeLimit ) {
    //Increment part number
                        pService->muint8PartNumber++;
                    }
                    if ( blnOpen == true ) {
    //Get just the file name
                        int intFile = strExisting.lastIndexOf(qcSeperator);
                        strExisting = strExisting.mid(intFile + 1);
    //Remove the extension
                        strExisting = strExisting.mid(0, strExisting.indexOf("."));
                    }
                    if ( blnOpen != true || strExisting.compare(strFileName) != 0 ) {
                        if ( blnOpen == true ) {
                            pService->blnFileClose();
                            blnOpen = false;
                        }
                        pService->muint8PartNumber = 1;
                    }
    //Append part number
                    if ( blnOpen != true ) {
                        pService->blnSetFileName(strPath
                                               + strFileName
                                               + QString(".%1.log")
                                               .arg(pService->muint8PartNumber
                                                   ,3, intBase, qcPadding));
                    }
                }
    //Is file open?
                if ( pService->blnIsFileOpen(blnOpen) == true && blnOpen != true ) {
                    pService->blnOpenFile(blnOpen);
                }
                if ( blnOpen == true ) {
                    QTextStream ts(&pService->mFile);
                    ts << strLine.toLatin1().data() << "\r\n";
                }
            }
            bool blnToConsole;
            if ( pService->blnToConsole(blnToConsole) == true && blnToConsole == true ) {
    //Output to console
                std::cout << strLine.toLatin1().data() << "\n";
                std::cout << std::flush;
            }
        }
    }
    emit finished();
}

The problem I'm getting not is that as soon as the finished signal is emitted, the application halts on:

std::abort();

line 1914 of qlogging.cpp, is there anything I've done wrong here? I think the issue is because the thread hadn't finished before it was deleted...

I am reading up on how to properly wait until it is stopped. Changed connections to:

connect(clsDebugService::mspThread, &QThread::started
                            ,this, &clsDebugService::process);
connect(this, &clsDebugService::finished
                            ,clsDebugService::mspThread, &QThread::quit);
connect(clsDebugService::mspThread, &QThread::finished
                            ,this, &clsDebugService::cleanup);

For some reason when I look at the stack tract I see:

 qFatal("QThread: Destroyed while thread is still running");

KroMignon · 16 Dec 2020, 18:18

@SPlatten said in Timer with Lambda function:

For some reason when I look at the stack tract I see:

As I wrote before, QThread is a QObject which is managing a thread. You should never use delete with a QObject instance but use QObject::deleteLater() which will ensure instance will be deleted in his working thread.

I would suggest you to change clsDebugService::cleanup():

void clsDebugService::cleanup() {
    if(clsDebugService::mspThread)
        clsDebugService::mspThread->deleteLater();
    clsDebugService::mspThread = nullptr;
}

SPlatten · wrote on 16 Dec 2020, 18:18

@KroMignon after calling deleteLater is it still ok to set mspThread to nullptr ?

I've changed the clean up to:

    if ( clsDebugService::mspThread != nullptr ) {
        clsDebugService::mspThread->deleteLater();
        clsDebugService::mspThread = nullptr;
    }

Now I'm seeing in the Application Output:

QObject::moveToThread: Current thread (0x101e67a70) is not the object's thread (0x0).
Cannot move to target thread (0x101e91530)

You might be loading two sets of Qt binaries into the same process. Check that all plugins are compiled against the right Qt binaries. Export DYLD_PRINT_LIBRARIES=1 and check that only one set of binaries are being loaded.

When all the debug messages have been displayed, a new debug message will cause the thread to be created again, I think this is what causes the above message.

Is it because the moveToThread function is called again for the same class again?

Ok, I've fixed it, I don't allow the thread to be deleted at all, until the application is terminated, all I do now is restart the thread as long as the thread ptr exists.

Christian Ehrlicher · wrote on 16 Dec 2020, 18:47

@KroMignon said in Timer with Lambda function:

Great to see that you are starting reading documentation.

ROFL

SimonSchroeder · wrote on 17 Dec 2020, 08:01

I usually just call exit() on the thread to stop the event loop, i.e. clsDebugService::mspThread->exit() in your case. Then there is some special quirk with QThreads: You can connect the thread's finished signal with the thread's deleteLater slot. Before the event loop actually stops it will first still handle the deleteLater slot for the thread:

connect(clsDebugService::mspThread, &QThread::finished, clsDebugService::mspThread, &QThread::deleteLater);

This is how you can clean up the thread once your done.