Signal emit causes segmentation fault

[Martikai]

The reference is valid when I check it with the debugger. The backtrace is added to my previous message.

[high_flyer]

I created a whole new test signal that contains an integer which is not connected anywhere and it still causes the exact same segmentation fault.

The backtrace without the code helps very little.
Please post the code that corresponds to the backtrace, and if it is not very long, post all of it, don't "meta code" it as it masks what you are doing wrong.

[Martikai]

The test signal is not connected anywhere. The crash still happens at the same function after emit which is

// SIGNAL 0
void LidarSub::test(int _t1)
{
    void *_a[] = { Q_NULLPTR, const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
    QMetaObject::activate(this, &staticMetaObject, 0, _a);
}

// SIGNAL 0
void LidarSub::test(int _t1)
{
    void *_a[] = { Q_NULLPTR, const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
    QMetaObject::activate(this, &staticMetaObject, 0, _a);
}

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lidarsub.h:

#ifndef LIDARSUB_H
#define LIDARSUB_H
 
#include "observation.h"
#include <QThread>
#include <QObject>
 
#include <ace/Log_Msg.h>
 
#include <dds/DdsDcpsInfrastructureC.h>
#include <dds/DdsDcpsPublicationC.h>
 
#include <dds/DCPS/Marked_Default_Qos.h>
#include <dds/DCPS/Service_Participant.h>
#include <dds/DCPS/WaitSet.h>
 
#include "dds/DCPS/StaticIncludes.h"
 
#include "/home/vtt/IDL/idl_lidar/lidarScanTypeSupportImpl.h"
 
class LidarSub: public QThread
{
    Q_OBJECT
 
signals:
    void test(int i);
 
public:
    LidarSub();
    int     create();
    void    destroy();
    void    lidarDataConverter(LidarScan::Observation newObs);
 
protected:
    virtual void run();
 
private:
    DDS::DomainParticipantFactory_var    dpf_;
    DDS::DomainParticipant_var           participant_;
    DDS::DataReader_var                  reader_;
    LidarScan::ObservationDataReader_var reader_i_;
 
    int numOfRecObs_;
 
};
#endif // LIDARSUB_H

#ifndef LIDARSUB_H
#define LIDARSUB_H

#include "observation.h"
#include <QThread>
#include <QObject>

#include <ace/Log_Msg.h>

#include <dds/DdsDcpsInfrastructureC.h>
#include <dds/DdsDcpsPublicationC.h>

#include <dds/DCPS/Marked_Default_Qos.h>
#include <dds/DCPS/Service_Participant.h>
#include <dds/DCPS/WaitSet.h>

#include "dds/DCPS/StaticIncludes.h"

#include "/home/vtt/IDL/idl_lidar/lidarScanTypeSupportImpl.h"

class LidarSub: public QThread
{
    Q_OBJECT

signals:
    void test(int i);

public:
    LidarSub();
    int     create();
    void    destroy();
    void    lidarDataConverter(LidarScan::Observation newObs);

protected:
    virtual void run();

private:
    DDS::DomainParticipantFactory_var    dpf_;
    DDS::DomainParticipant_var           participant_;
    DDS::DataReader_var                  reader_;
    LidarScan::ObservationDataReader_var reader_i_;

    int numOfRecObs_;

};
#endif // LIDARSUB_H

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lidarsub.cpp:

#include "lidarsub.h"
 
#include <QDebug>
#include <QThread>
 
#include <ace/Log_Msg.h>
 
#include <dds/DdsDcpsInfrastructureC.h>
#include <dds/DdsDcpsPublicationC.h>
 
#include <dds/DCPS/Marked_Default_Qos.h>
#include <dds/DCPS/Service_Participant.h>
#include <dds/DCPS/WaitSet.h>
 
#include "dds/DCPS/StaticIncludes.h"
 
#include "/home/vtt/IDL/idl_lidar/lidarScanTypeSupportImpl.h"
#include "/home/vtt/IDL/idl_lidar/DataReaderListenerImpl.h"
 
 
using namespace DDS;
using namespace std;
 
void LidarSub::lidarDataConverter(LidarScan::Observation newObs)
{
    int i = 0;
    emit test(i); // <- This causes the segmentation fault
}
 
LidarSub::LidarSub()
{
    numOfRecObs_ = 0;
}
 
int LidarSub::create()
{
    // OpenDDS related code that initiates the DDS configuration. Can't publish this part of the code on this forum.
    // This should not affect anything else than the DDS communication.
}
 
 
void LidarSub::destroy()
{
    TheServiceParticipant->shutdown();
}
 
void LidarSub::run()
{
        while (true) {
 
            QThread::msleep(10);
        }
}

#include "lidarsub.h"

#include <QDebug>
#include <QThread>

#include <ace/Log_Msg.h>

#include <dds/DdsDcpsInfrastructureC.h>
#include <dds/DdsDcpsPublicationC.h>

#include <dds/DCPS/Marked_Default_Qos.h>
#include <dds/DCPS/Service_Participant.h>
#include <dds/DCPS/WaitSet.h>

#include "dds/DCPS/StaticIncludes.h"

#include "/home/vtt/IDL/idl_lidar/lidarScanTypeSupportImpl.h"
#include "/home/vtt/IDL/idl_lidar/DataReaderListenerImpl.h"


using namespace DDS;
using namespace std;

void LidarSub::lidarDataConverter(LidarScan::Observation newObs)
{
    int i = 0;
    emit test(i); // <- This causes the segmentation fault
}

LidarSub::LidarSub()
{
    numOfRecObs_ = 0;
}

int LidarSub::create()
{
    // OpenDDS related code that initiates the DDS configuration. Can't publish this part of the code on this forum.
    // This should not affect anything else than the DDS communication.
}


void LidarSub::destroy()
{
    TheServiceParticipant->shutdown();
}

void LidarSub::run()
{
        while (true) {

            QThread::msleep(10);
        }
}

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DataReaderListenerImpl.cpp - function that is called when new data arrives through DDS
handle_ is pointer to the instantiation of LidarSub class

void DataReaderListenerImpl::on_data_available(DDS::DataReader_ptr reader)
{
    LidarScan::ObservationDataReader_var reader_i =
        LidarScan::ObservationDataReader::_narrow(reader);
 
    if ( !reader_i )
    {
        ACE_ERROR((LM_ERROR,
                ACE_TEXT("ERROR: %N:%l: on_data_available() -")
                ACE_TEXT(" _narrow failed!\n")));
        ACE_OS::exit(-1);
    }
 
 
    LidarScan::Observation newObs;
    DDS::SampleInfo info;
 
    DDS::ReturnCode_t error = reader_i->take_next_sample(newObs, info);
 
    if (error == DDS::RETCODE_OK)
    {
 
        if ( info.valid_data )
        {
            if ( handle_ != NULL )
            {
                handle_->lidarDataConverter(newObs);
            }
        }
 
    } else
    {
        ACE_ERROR((LM_ERROR,
                ACE_TEXT("ERROR: %N:%l: on_data_available() -")
                ACE_TEXT(" take_next_sample failed!\n")));
    }
}

void DataReaderListenerImpl::on_data_available(DDS::DataReader_ptr reader)
{
    LidarScan::ObservationDataReader_var reader_i =
        LidarScan::ObservationDataReader::_narrow(reader);

    if ( !reader_i )
    {
        ACE_ERROR((LM_ERROR,
                ACE_TEXT("ERROR: %N:%l: on_data_available() -")
                ACE_TEXT(" _narrow failed!\n")));
        ACE_OS::exit(-1);
    }


    LidarScan::Observation newObs;
    DDS::SampleInfo info;

    DDS::ReturnCode_t error = reader_i->take_next_sample(newObs, info);

    if (error == DDS::RETCODE_OK)
    {

        if ( info.valid_data )
        {
            if ( handle_ != NULL )
            {
                handle_->lidarDataConverter(newObs);
            }
        }

    } else
    {
        ACE_ERROR((LM_ERROR,
                ACE_TEXT("ERROR: %N:%l: on_data_available() -")
                ACE_TEXT(" take_next_sample failed!\n")));
    }
}

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[wysota]

Does handle_ point to a valid object?

[Martikai]

Does handle_ point to a valid object?

No, thank you! I had forgotten about setting the actual pointer. For some reason the DataReaderListenerImpl is able to call the lidarDataConverter() even though the pointer is not a valid object.

[wysota]

It's a non-virtual function so it doesn't need a proper object to call it. But when you try accessing any data, you end up with reading garbage.