emit a signal from inside a callback routine

[franco.amato]

Hi to all,
I' writing an audio editor using fmod and Qt.
Hi have a fmod callback that's called by the fmod engine when a sound is stopped to play and from it I would emit a signal.
Here the callback that's part of a class:

class AudioDevice : public QObject
{
	Q_OBJECT
 
public:
static FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
		                               unsigned int commanddata1, unsigned int commanddata2)
	{
		(void)commanddata1; // Unused (to avoid warnings)
		(void)commanddata2; // Unused (to avoid warnings)
 
		SoundData* currentSound; 
 
		switch(type)
		{
		case FMOD_CHANNEL_CALLBACKTYPE_END:
			{
				FMOD_RESULT result;
				FMOD::Channel *currentChannel = (FMOD::Channel *)channel;
 
				void *ud = NULL;
				result = currentChannel->getUserData( &ud );
 
				currentSound = (SoundData*)ud;
 
				/* inform that sound stopped */
				emit( soundStopped() );// <------- THIS ONE
				break;
			}
		default:
			break;
		}
 
		return FMOD_OK;
	}
public slots:
	// Initialize the audio system
	bool init();
 
signals:
	void soundStopped();
..more code...

class AudioDevice : public QObject
{
	Q_OBJECT

public:
static FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
		                               unsigned int commanddata1, unsigned int commanddata2)
	{
		(void)commanddata1; // Unused (to avoid warnings)
		(void)commanddata2; // Unused (to avoid warnings)

		SoundData* currentSound; 

		switch(type)
		{
		case FMOD_CHANNEL_CALLBACKTYPE_END:
			{
				FMOD_RESULT result;
				FMOD::Channel *currentChannel = (FMOD::Channel *)channel;

				void *ud = NULL;
				result = currentChannel->getUserData( &ud );

				currentSound = (SoundData*)ud;

				/* inform that sound stopped */
				emit( soundStopped() );// <------- THIS ONE
				break;
			}
		default:
			break;
		}

		return FMOD_OK;
	}
public slots:
	// Initialize the audio system
	bool init();

signals:
	void soundStopped();
..more code...

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The compiler don't like the emit call.
It says

error C2352: 'AudioDevice::soundStopped' : illegal call of non-static member function

How can I do?

Best

[JohannesMunk]

Hi!

The compiler is correct. You are calling a non static member from inside a static function. That's a no go. What would be the this object of that call?

Your callback probably cannot be non-static, so you will have to reference your audiodevice in another way.

Usually you would use the "user-data" of the callback for that. When you set the callback up, you can pass a pointer to your Audiodevice as commanddata1.

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
signals:
    void soundStopped();
protected:
    void DoEndCallBack() {emit soundStopped();}
}
 
..
 
FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
    AudioDevice* ad = dynamic_cast<AudioDevice*>(commanddata1);
    if (ad)
      ad->DoEndCallBack();
   ..
}

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
signals:
    void soundStopped();
protected:
    void DoEndCallBack() {emit soundStopped();}
}

..

FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
    AudioDevice* ad = dynamic_cast<AudioDevice*>(commanddata1);
    if (ad)
      ad->DoEndCallBack();
   ..
}

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Using the friends approach you can even declare the DoEndCallBack protected..

HIH

Johannes

[franco.amato]

Hi!

The compiler is correct. You are calling a non static member from inside a static function. That's a no go. What would be the this object of that call?

Your callback probably cannot be non-static, so you will have to reference your audiodevice in another way.

Usually you would use the "user-data" of the callback for that. When you set the callback up, you can pass a pointer to your Audiodevice as commanddata1.

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
signals:
    void soundStopped();
protected:
    void DoEndCallBack() {emit soundStopped();}
}
 
..
 
FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
    AudioDevice* ad = dynamic_cast<AudioDevice*>(commanddata1);
    if (ad)
      ad->DoEndCallBack();
   ..
}

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
signals:
    void soundStopped();
protected:
    void DoEndCallBack() {emit soundStopped();}
}

..

FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
    AudioDevice* ad = dynamic_cast<AudioDevice*>(commanddata1);
    if (ad)
      ad->DoEndCallBack();
   ..
}

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Using the friends approach you can even declare the DoEndCallBack protected..

HIH

Johannes

Hi thank you very much.
I didn't understand. What does the DoEndCallback do?
Sorry but in this case commanddata1 and commanddata2 are always 0.
This is the part where I use the userdata:

case FMOD_CHANNEL_CALLBACKTYPE_END:
		{
			FMOD_RESULT result;
			FMOD::Channel *currentChannel = (FMOD::Channel *)channel;
 
			void *ud = NULL;
			result = currentChannel->getUserData( &ud ); //<---USERDATA
 
			currentSound = (SoundData*)ud;
 
			/* inform that sound stopped */
			currentSound->soundFinished(); //<-- I call a routine instead of emiting signals
			break;
		}

case FMOD_CHANNEL_CALLBACKTYPE_END:
		{
			FMOD_RESULT result;
			FMOD::Channel *currentChannel = (FMOD::Channel *)channel;

			void *ud = NULL;
			result = currentChannel->getUserData( &ud ); //<---USERDATA

			currentSound = (SoundData*)ud;

			/* inform that sound stopped */
			currentSound->soundFinished(); //<-- I call a routine instead of emiting signals
			break;
		}

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but I don't cast it to an AudioDevice type. AudioDevice is a singleton.
I cast to a SoundData type ( in my example )..

Is a bit difficult. May be I can not use signals in this case

[Tanuki-no Torigava]

Hi. When I met the same problem I solved that with startTimer/killTimer and void timerEvent ( QTimerEvent * event ) reimplementation. Then what you can do is to set any Boolean variable (or QMutex based variable if you have multiple access) to true (lock) accordingly and process that inside timerEvent.

Typical solution might be:

static const int timeScale = 50; // 50 Msec
 
class A: public QObject
{
    Q_OBJECT
 
public:
 
    Q_INVOKABLE A( QObject * parent = 0 )
        : QObject(parent),
          m_check(false),
          m_timer(0)
    {
        m_timer = startTimer(timeScale);
    }
    ~A()
    {
       if (m_timer > 0)
           killTimer(m_timer);
    }
 
public slots:
 
     void handler()
     {
          if (m_check)
              return;
// do something here
          m_check = true;
     }
 
protected:
     void timerEvent ( QTimerEvent * event)
     {
          if (m_check)
          {
              // do something
              emit some_signal(some_args);
              m_check != m_check; // Just  quicker
          }
     }
private:
 
bool m_check;
int   m_timer;
}

static const int timeScale = 50; // 50 Msec

class A: public QObject
{
    Q_OBJECT

public:

    Q_INVOKABLE A( QObject * parent = 0 )
        : QObject(parent),
          m_check(false),
          m_timer(0)
    {
        m_timer = startTimer(timeScale);
    }
    ~A()
    {
       if (m_timer > 0)
           killTimer(m_timer);
    }

public slots:

     void handler()
     {
          if (m_check)
              return;
// do something here
          m_check = true;
     }

protected:
     void timerEvent ( QTimerEvent * event)
     {
          if (m_check)
          {
              // do something
              emit some_signal(some_args);
              m_check != m_check; // Just  quicker
          }
     }
private:

bool m_check;
int   m_timer;
}

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Good luck.

[franco.amato]

Hi. When I met the same problem I solved that with startTimer/killTimer and void timerEvent ( QTimerEvent * event ) reimplementation. Then what you can do is to set any Boolean variable (or QMutex based variable if you have multiple access) to true (lock) accordingly and process that inside timerEvent.

Typical solution might be:

static const int timeScale = 50; // 50 Msec
 
class A: public QObject
{
    Q_OBJECT
 
public:
 
    Q_INVOKABLE A( QObject * parent = 0 )
        : QObject(parent),
          m_check(false),
          m_timer(0)
    {
        m_timer = startTimer(timeScale);
    }
    ~A()
    {
       if (m_timer > 0)
           killTimer(m_timer);
    }
 
public slots:
 
     void handler()
     {
          if (m_check)
              return;
// do something here
          m_check = true;
     }
 
protected:
     void timerEvent ( QTimerEvent * event)
     {
          if (m_check)
          {
              // do something
              emit some_signal(some_args);
              m_check != m_check; // Just  quicker
          }
     }
private:
 
bool m_check;
int   m_timer;
}

static const int timeScale = 50; // 50 Msec

class A: public QObject
{
    Q_OBJECT

public:

    Q_INVOKABLE A( QObject * parent = 0 )
        : QObject(parent),
          m_check(false),
          m_timer(0)
    {
        m_timer = startTimer(timeScale);
    }
    ~A()
    {
       if (m_timer > 0)
           killTimer(m_timer);
    }

public slots:

     void handler()
     {
          if (m_check)
              return;
// do something here
          m_check = true;
     }

protected:
     void timerEvent ( QTimerEvent * event)
     {
          if (m_check)
          {
              // do something
              emit some_signal(some_args);
              m_check != m_check; // Just  quicker
          }
     }
private:

bool m_check;
int   m_timer;
}

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Good luck.

I don't know how to adapt your code for my purpose, but how can be possible to connect
a slot of an object that's created when the gui is started with a signal of an object that is created later?
I get an error

[Tanuki-no Torigava]

I don't know how to adapt your code for my purpose, but how can be possible to connect
a slot of an object that's created when the gui is started with a signal of an object that is created later?
I get an error

That is easy. Let's say you create object B from some method of the object A, so it will look like that:

A::someMethod()
{
    B* b = new B(this);
    connect(b, SIGNAL(b_signal(mask)), this, SLOT(signal_handler);
 
}

A::someMethod()
{
    B* b = new B(this);
    connect(b, SIGNAL(b_signal(mask)), this, SLOT(signal_handler);

}

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So, you get the idea.

[franco.amato]

That is easy. Let's say you create object B from some method of the object A, so it will look like that:

A::someMethod()
{
    B* b = new B(this);
    connect(b, SIGNAL(b_signal(mask)), this, SLOT(signal_handler);
 
}

A::someMethod()
{
    B* b = new B(this);
    connect(b, SIGNAL(b_signal(mask)), this, SLOT(signal_handler);

}

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So, you get the idea.

Hi yes,
but what the key "mask" means?
Seems that I have to connect after the new

[JohannesMunk]

Hi there!

You seem to miss the point of the commanddata.. That is data you pass along / define once when you call the callback-setup! You seem to pass 0 at the moment, that is why its zero. Just pass a pointer to your AudioDevice and it should work. That pointer-data then is passed to the callback each time it is called. At least that is, how callbacks usually work..

You should have mentioned, that AudioDevice is a singleton.. Because than you can call the DoEndCallBack directly, even if your callback doesn't provide a user-defined-data (which I think it does => commanddata).

protected:
void DoEndCallBack() {emit soundStopped();}

DoEndCallback just emits the soundStopped signal, as I defined it... But you can of course code it directly, see below:

Let me give you a more complete Callback scenario:

class TDAQCaptureThread : public QThread
{
  friend int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
  Q_OBJECT
  signals:
    void Finished();
  protected:
    void run();
};
 
#include "DAQCaptureThread.h"
 
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
 
void TDAQCaptureThread::run()
{   
  ...
 
  DAQmxRegisterDoneEvent(taskHandle,1,DoneCallback,this);
 
  ..
 
  DAQmxStartTask(taskHandle);
 
  exec();
 
  ...
 
}
 
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData)
{
  ..  
 
  emit ((TDAQCaptureThread*)callbackData)->Finished();
 
  ...
 
  return 0;
}

class TDAQCaptureThread : public QThread
{
  friend int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
  Q_OBJECT
  signals:
    void Finished();
  protected:
    void run();
};

#include "DAQCaptureThread.h"

int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);

void TDAQCaptureThread::run()
{   
  ...

  DAQmxRegisterDoneEvent(taskHandle,1,DoneCallback,this);
  
  ..
  
  DAQmxStartTask(taskHandle);

  exec();
  
  ...
               
}

int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData)
{
  ..  
  
  emit ((TDAQCaptureThread*)callbackData)->Finished();
  
  ...

  return 0;
}

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The DAQmxRegisterDoneEvent is defined int the used DAQmx library as follows:

int32 __CFUNC DAQmxRegisterDoneEvent(TaskHandle task, uInt32 options, DAQmxDoneEventCallbackPtr callbackFunction, void *callbackData);

int32 __CFUNC DAQmxRegisterDoneEvent(TaskHandle task, uInt32 options, DAQmxDoneEventCallbackPtr callbackFunction, void *callbackData);

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This callbackData is what I'm talking about.. If you decide one day to have several AudioDevices :->

HIH

Johannes

[franco.amato]

Hi there!

You seem to miss the point of the commanddata.. That is data you pass along / define once when you call the callback-setup! You seem to pass 0 at the moment, that is why its zero. Just pass a pointer to your AudioDevice and it should work. That pointer-data then is passed to the callback each time it is called. At least that is, how callbacks usually work..

You should have mentioned, that AudioDevice is a singleton.. Because than you can call the DoEndCallBack directly, even if your callback doesn't provide a user-defined-data (which I think it does => commanddata).

protected:
void DoEndCallBack() {emit soundStopped();}

DoEndCallback just emits the soundStopped signal, as I defined it... But you can of course code it directly, see below:

Let me give you a more complete Callback scenario:

class TDAQCaptureThread : public QThread
{
  friend int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
  Q_OBJECT
  signals:
    void Finished();
  protected:
    void run();
};
 
#include "DAQCaptureThread.h"
 
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
 
void TDAQCaptureThread::run()
{   
  ...
 
  DAQmxRegisterDoneEvent(taskHandle,1,DoneCallback,this);
 
  ..
 
  DAQmxStartTask(taskHandle);
 
  exec();
 
  ...
 
}
 
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData)
{
  ..  
 
  emit ((TDAQCaptureThread*)callbackData)->Finished();
 
  ...
 
  return 0;
}

class TDAQCaptureThread : public QThread
{
  friend int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);
  Q_OBJECT
  signals:
    void Finished();
  protected:
    void run();
};

#include "DAQCaptureThread.h"

int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData);

void TDAQCaptureThread::run()
{   
  ...

  DAQmxRegisterDoneEvent(taskHandle,1,DoneCallback,this);
  
  ..
  
  DAQmxStartTask(taskHandle);

  exec();
  
  ...
               
}

int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData)
{
  ..  
  
  emit ((TDAQCaptureThread*)callbackData)->Finished();
  
  ...

  return 0;
}

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The DAQmxRegisterDoneEvent is defined int the used DAQmx library as follows:

int32 __CFUNC DAQmxRegisterDoneEvent(TaskHandle task, uInt32 options, DAQmxDoneEventCallbackPtr callbackFunction, void *callbackData);

int32 __CFUNC DAQmxRegisterDoneEvent(TaskHandle task, uInt32 options, DAQmxDoneEventCallbackPtr callbackFunction, void *callbackData);

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This callbackData is what I'm talking about.. If you decide one day to have several AudioDevices :->

HIH

Johannes

In this case commanddata1 and commanddata2 are not the user data ( fmod callbacks ). In this case they are 0. User data are sent by another routine setUserdata and I got it from inside the callback by getUserdData() .

Thank you

[JohannesMunk]

All right, I give up :->

So your solution is to just emit the signal through the singleton?

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
 
   public:
     static AudioDevice* singleton()
     {
      if (!instance)
        instance = new AudioDevice();
      return instance;
     }
   signals:
     void soundStopped();
 
   protected:
     AudioDevice() {}
 
   private:
     static AudioDevice *instance;
};
 
AudioDevice* AudioDevice::instance = 0;
 
FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
  ..
  emit AudioDevice::singleton()->soundStopped();
  ..
}

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);

   public:
     static AudioDevice* singleton()
     {
      if (!instance)
        instance = new AudioDevice();
      return instance;
     }
   signals:
     void soundStopped();

   protected:
     AudioDevice() {}

   private:
     static AudioDevice *instance;
};

AudioDevice* AudioDevice::instance = 0;

FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
  ..
  emit AudioDevice::singleton()->soundStopped();
  ..
}

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HIH

Johannes

[franco.amato]

All right, I give up :->

So your solution is to just emit the signal through the singleton?

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);
 
   public:
     static AudioDevice* singleton()
     {
      if (!instance)
        instance = new AudioDevice();
      return instance;
     }
   signals:
     void soundStopped();
 
   protected:
     AudioDevice() {}
 
   private:
     static AudioDevice *instance;
};
 
AudioDevice* AudioDevice::instance = 0;
 
FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
  ..
  emit AudioDevice::singleton()->soundStopped();
  ..
}

class AudioDevice : public QObject
{ Q_OBJECT
  friend FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2);

   public:
     static AudioDevice* singleton()
     {
      if (!instance)
        instance = new AudioDevice();
      return instance;
     }
   signals:
     void soundStopped();

   protected:
     AudioDevice() {}

   private:
     static AudioDevice *instance;
};

AudioDevice* AudioDevice::instance = 0;

FMOD_RESULT F_CALLBACK endCallback(FMOD_CHANNEL *channel, FMOD_CHANNEL_CALLBACKTYPE type, 
                                       unsigned int commanddata1, unsigned int commanddata2)
{
  ..
  emit AudioDevice::singleton()->soundStopped();
  ..
}

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HIH

Johannes

Hi I didn't well understand the difference between your last code and the code you suggested to me before.
Can you explain to me?
Best Regards