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Getting SIGSEGV on "finished" signal from QNetwowkAccessManager

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  • F Offline
    F Offline
    Fernando
    wrote on last edited by
    #1

    Hi everyone,

    long time lurker, first time poster. :-)

    I'm using QT 5.4.1 under Windows7-64.

    I have a serious problem with QNetworkAccessManager: I got SIGSEGV when the "finished" signal fires, but only in Debug mode!! :-(

    My sample:

    mainwindow.h

    #ifndef MAINWINDOW_H
    #define MAINWINDOW_H

    #include <QMainWindow>
    #include <QNetworkAccessManager>
    #include <QNetworkReply>
    #include <QNetworkRequest>
    #include <QFile>
    #include <QDebug>

    #define TEST_URL "http://www.gnu.org/licenses/gpl-3.0.txt"

    namespace Ui {
    class MainWindow;
    }

    class MainWindow : public QMainWindow
    {
    Q_OBJECT

    public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    private:
    Ui::MainWindow *ui;

    QNetworkAccessManager* mpNetManager;
    
    void initializeNetwork();
    
    void testDownload();
    

    private slots:
    void downloadFinished(QNetworkReply*);
    };

    #endif // MAINWINDOW_H

    mainwindow.cpp

    #include "mainwindow.h"
    #include "ui_mainwindow.h"

    MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
    {
    ui->setupUi(this);
    initializeNetwork();
    testDownload();
    }

    MainWindow::~MainWindow()
    {
    delete ui;
    mpNetManager->deleteLater();
    }

    void MainWindow::initializeNetwork()
    {
    mpNetManager = new QNetworkAccessManager;
    }

    void MainWindow::testDownload()
    {
    if (mpNetManager)
    {
    QNetworkRequest netRequest;
    QUrl downloadURL(TEST_URL);
    netRequest.setUrl(downloadURL);
    connect(mpNetManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadFinished()));
    mpNetManager->get(netRequest);
    }
    }

    void MainWindow::downloadFinished (QNetworkReply* pNetReply)
    {
    if (pNetReply)
    {
    if(pNetReply->error())
    {
    qDebug() << "ERROR!";
    qDebug() << pNetReply->errorString();
    }
    else
    {
    QString qsDownloadPath = "downloaded.txt";
    QFile *pOutFile = new QFile(qsDownloadPath);
    if(pOutFile->open(QFile::WriteOnly))
    {
    pOutFile->write(pNetReply->readAll());
    pOutFile->flush();
    pOutFile->close();
    }
    delete pOutFile;
    qDebug() << "Download finished";
    qDebug() << "Content written to";
    qDebug() << qsDownloadPath;
    }
    pNetReply->deleteLater();
    }
    }

    I'm getting mad: it runs fine in Release, but when i launch the debugger, I get the message

    "The inferior stopped because it received a signal from the operating system
    Signal name: SIGSEGV
    Signal meaning: Segmentation Fault"

    I'm not new to Qt, but I'm new to everything QNetwork. :-(

    Thanks a lot!

    Fernando

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    0
    • SGaistS Offline
      SGaistS Offline
      SGaist
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi and welcome to devnet,

      connect(mpNetManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(downloadFinished()));

      You are missing the parameter of downloadFinished

      Interested in AI ? www.idiap.ch
      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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      • F Offline
        F Offline
        Fernando
        wrote on last edited by SGaist
        #3

        You're right, sorry.

        Corrected .cpp source (still the same problem):

        #include "mainwindow.h"
        #include "ui_mainwindow.h"
        
        MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
        {
            ui->setupUi(this);
            initializeNetwork();
            testDownload();
        }
        
        
        MainWindow::~MainWindow()
        {
            delete ui;
            mpNetManager->deleteLater();
        }
        
        
        void MainWindow::initializeNetwork()
        {
            mpNetManager = new QNetworkAccessManager;
        }
        
        
        void MainWindow::testDownload()
        {
            if (mpNetManager)
            {
                QNetworkRequest netRequest;
                QUrl downloadURL(TEST_URL);
                netRequest.setUrl(downloadURL);
                connect(mpNetManager, SIGNAL(finished(QNetworkReply * )), this, SLOT(downloadFinished(QNetworkReply * )));
                mpNetManager->get(netRequest);
            }
        }
        
        
        void MainWindow::downloadFinished (QNetworkReply* pNetReply)
        {
            if (pNetReply)
            {
                if(pNetReply->error())
                {
                        qDebug() << "ERROR!";
                        qDebug() << pNetReply->errorString();
                }
                else
                {
                    QString    qsDownloadPath = "downloaded.txt";
                    QFile *pOutFile = new QFile(qsDownloadPath);
                    if(pOutFile->open(QFile::WriteOnly))
                    {
                        pOutFile->write(pNetReply->readAll());
                        pOutFile->flush();
                        pOutFile->close();
                    }
                    delete pOutFile;
                        qDebug() << "Download finished";
                        qDebug() << "Content written to";
                        qDebug() << qsDownloadPath;
                }
                pNetReply->deleteLater();
            }
        }
        

        [edit: Added missing coding tags SGaist]

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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by
          #4

          What do you get if you run your application through a debugger ?

          Interested in AI ? www.idiap.ch
          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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          • F Offline
            F Offline
            Fernando
            wrote on last edited by
            #5

            As I stated, when i launch the debugger, as soon as the "finished" signal fires I get the message

            "The inferior stopped because it received a signal from the operating system
            Signal name: SIGSEGV
            Signal meaning: Segmentation Fault"

            This is from C:\Windows\SysWOW64\ntdll.dll, instruction "rtlmovmemory"

            This only happens while debugging: the program runs fine in Release.

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            • SGaistS Offline
              SGaistS Offline
              SGaist
              Lifetime Qt Champion
              wrote on last edited by
              #6

              Can you check with a tool like Dependency Walker the libraries you are currently linking to ?

              Interested in AI ? www.idiap.ch
              Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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              • F Offline
                F Offline
                Fernando
                wrote on last edited by
                #7

                Sure:

                LIBGCC_S_DW2-1.DLL
                QT5CORED.DLL
                QT5NETWORKD.DLL
                QT5WIDGETSD.DLL
                API-MS-WIN-APPMODEL-RUNTIME-L1-1-0.DLL
                API-MS-WIN-CORE-WINRT-ERROR-L1-1-0.DLL
                API-MS-WIN-CORE-WINRT-L1-1-0.DLL
                API-MS-WIN-CORE-WINRT-ROBUFFER-L1-1-0.DLL
                API-MS-WIN-CORE-WINRT-STRING-L1-1-0.DLL
                API-MS-WIN-SHCORE-SCALING-L1-1-1.DLL
                DCOMP.DLL
                IESHIMS.DLL

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                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #8

                  That part looks good

                  Then let's get step by step. Does it also fail if you comment out the network stuff ?

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • F Offline
                    F Offline
                    Fernando
                    wrote on last edited by Fernando
                    #9

                    It debugs nicely without

                    mpNetManager->get(netRequest);

                    And it runs nicely (even with mpNetManager->get(netRequest)) when not debugging (even if the build was in debug mode).
                    To me, it's a bug in the debugger :-) , at least under Windows7-64.

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                    • SGaistS Offline
                      SGaistS Offline
                      SGaist
                      Lifetime Qt Champion
                      wrote on last edited by
                      #10

                      Using Qt's MinGW package ?

                      Interested in AI ? www.idiap.ch
                      Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • F Offline
                        F Offline
                        Fernando
                        wrote on last edited by
                        #11

                        Sorry, I was out of town.

                        Yes, using Qt's MinGW package (I don't have and don't like Visual Studio :-) ).

                        1 Reply Last reply
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                        • SGaistS Offline
                          SGaistS Offline
                          SGaist
                          Lifetime Qt Champion
                          wrote on last edited by
                          #12

                          So you have MinGW 4.9 ?

                          Interested in AI ? www.idiap.ch
                          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

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                          • F Offline
                            F Offline
                            Fernando
                            wrote on last edited by
                            #13

                            Yes, MinGW 4.9.1.
                            Do you think I should file a bug report?

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