Wireshark · Wireshark-dev: [Wireshark-dev] Slot on main thread not called when signal is emitted from another thread

[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

I am trying to write a plugin for Wireshark that will run a TCP server on a service thread.  The TCP server will receive a new frame number from another application and then use the Plugin IF function plugin_if_goto_frame to cause Wireshark to jump to the new frame number.  I have found through various experiments that plugin_if_goto_frame must run on the main thread.  I'm writing the plugin in Qt and C++, exposing the callbacks using extern "C" declarations. The callbacks are being called correctly and that all looks fine.

 

I’m using a Qt cross-thread (QueuedConnection) signal and slot to communicate between my service thread and the main thread.  The problem I am having is that although the service thread emits the signal (well it executes the instruction) the slot in the main thread doesn’t get called.  I’ve removed all of the TCP server code to simplify things.  The relevant bits of the code looks like this:

 

syncro.h

 

#ifndef SYNCRO_H

#define SYNCRO_H

#include <QtCore>

 

#include "mythread.h"

 

class Syncro : public QObject

{

    Q_OBJECT

 

public:

    void Initialise(MyThread *);

 

public slots:

    void jumpToFrame(int);

};

 

#endif // SYNCRO_H

 

 

syncro.cpp

 

#include <plugin_if.h>

 

#include "syncro.h"

#include <QtCore>

#include <QDebug>

 

void Syncro::Initialise(MyThread *serviceThread)

{

    // connect(serviceThread, SIGNAL(syncroGoFrame(int)), this, SLOT(jumpToFrame(int)), Qt::DirectConnection);

    connect(serviceThread, SIGNAL(syncroGoFrame(int)), this, SLOT(jumpToFrame(int)), Qt::QueuedConnection);

}

 

void Syncro::jumpToFrame(int new_frame)

{

    plugin_if_goto_frame(new_frame);

    return;

}

 

 

mythread.h

 

#ifndef MYTHREAD_H

#define MYTHREAD_H

#include <QtCore>

 

class MyThread : public QThread

{

    Q_OBJECT

 

public:

    MyThread();

    void run();

 

signals:

    void syncroGoFrame(int);

};

 

#endif // MYTHREAD_H

 

 

mythread.cpp

 

#include "mythread.h"

#include <QtCore>

#include <QDebug>

 

MyThread::MyThread()

{

 

}

 

void MyThread::run()

{

    while (true)

    {

        qDebug() << "Running";

        sleep(3);

        qDebug() << "Still Running";

        emit syncroGoFrame(22);

    }

}

 

packet-syncro.cpp

 

static int proto_syncro = -1;

static MyThread *serviceThread;

static Syncro *mainObject;

 

void

proto_register_syncro(void)

{

    module_t *syncro_module;

 

     proto_syncro = proto_register_protocol("Syncro Service",

        "Syncro",

        "syncro");

 

    syncro_module = prefs_register_protocol(proto_syncro, proto_reg_handoff_syncro);

 

    if (!serviceThread)

    {

        serviceThread = new MyThread;

        mainObject = new Syncro;

        mainObject->Initialise(serviceThread);

 

        serviceThread->start();

    }

 

    return;

}

 

 

When I run the code the extra thread starts OK and it starts to cycle around the loop with the 3 second sleep. However, the connected slot function Syncro::jumpToFrame(int new_frame) does not get called. If I change the connect from QueuedConnection to DirectConnection the slot function gets called but, as expected, in the context of my serviceThread. I need the slot function to run on the main thread.

 

I guess it is because my jumpToFrame slot function is not on the main thread event loop, but I don’t understand how to get it on the loop.

 

Any advice would be much appreciated.

 

Thanks and regards…Paul

 

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