one signal(or slot) connect to multiple slot(or signal),will it lost data?

[QtTester]

Hi, guys.
I have multiple camera and a class wrapper for them.
Here is my architechture:

// a thread to capture camera and process data, use signal to notify manager
class Thread
{
signals:
    void camSignal(QList<int> result,QImage img);
}

// an interface managing cameras and his threads
class CamManager
{
public:
  Thread a,b,c,d,e;
  void bind(){
    connect(&a,&Thread::camSignal,this,onCamSignal);
    // ...
    // also connect for b,c,d,e
  }
slot:
   void onCamSignal(QList<int> result,QImage img){
    // display...and other things
    // to external caller
    emit camSignalExternal(result,img, otherParams);
  }

// an interface for external caller
signals:
  void camSignalExternal(QList<int> result,QImage img,int others);
}

For external callers:

class Caller1
{
public:
    CamManager *cm;
   void init(){
    connect(cm,&CamManager:camSignalExternal,this,onCamSignal);
  }
// receive all cameras' data
slot:
  void onCamSignal(QList<int> result,QImage img,int others);
}

class Caller2
{
public:
    // same instance to Caller1
    CamManager *cm;
   void init(){
    connect(cm,&CamManager:camSignalExternal,this,onCamSignal);
  }
// receive all cameras' data
slot:
  void onCamSignal(QList<int> result,QImage img,int others);
}

My question are:
1、data from 'class Thread' to 'class CamManager ',will the slot lost data? If it lost data, should I use connect parameter 'Qt::UniqueConnection' ?
2、data from 'class CamManager ' to 'class Caller'，Qt::UniqueConnection is the best choise？
3、In there multiple signals to one slot, or one signal to multiple slots situation,
signal's parameter use &(reference) or pass value directly ,which one is better and has no risk to lost data?

//Fast reference method:
void camSignalExternal(const QList<int> &result,cosnt QImage &img);
// .VS. copying method:
void camSignalExternal(QList<int> result,QImage img);

any reply will be appreciated.

[jsulm]

@QtTester said in one signal(or slot) connect to multiple slot(or signal),will it lost data?:

data from 'class Thread' to 'class CamManager ',will the slot lost data?

1. No. Why should it loose data?
2. Signals/slots across threads automatically use Qt::QueuedConnection and you should not try to change that
3. You will not loose any data, doesn't matter whether you pass by reference or by value

[QtTester]

@jsulm said in one signal(or slot) connect to multiple slot(or signal),will it lost data?:

@QtTester said in one signal(or slot) connect to multiple slot(or signal),will it lost data?:

data from 'class Thread' to 'class CamManager ',will the slot lost data?

1. No. Why should it loose data?
2. Signals/slots across threads automatically use Qt::QueuedConnection and you should not try to change that
3. You will not loose any data, doesn't matter whether you pass by reference or by value

Thanks for so quickly reply.
I mean Qt::QueuedConnection but type wrong :-(
So I think pass by reference will be better?

[jsulm]

@QtTester said in one signal(or slot) connect to multiple slot(or signal),will it lost data?:

So I think pass by reference will be better?

Yes, use reference. But keep in mind that signal parameters are copied in case of signals/slots across thread.

[QtTester]

@jsulm