segmentation fault when subscribing to events
avatar par défaut
JCM
Hi,

i wrote a Device Server that subscribe to events with many device attributes and different data types… I implements only one callback method which is triggered when the events are received (push model).
I have an segmentation fault when receiving an event with data type different from the subscription one…
The problem comes from the allocation of the array in the cb.

i simply tried with tangotest and i have the same error ;(

extract of example subscribe event (data type of the attribute is DevDouble):


		      try
			{
			  the_device = new Tango::DeviceProxy("sys/tg_test/1");
			  if (the_device->state() == Tango::FAULT)
			    {
			      set_state(Tango::FAULT);
			    }
			  else
			    {
			    
			      cb = new DoubleEventCallBack();
			      if (cb!=NULL)
				event_id=the_device->subscribe_event("long_scalar_w",Tango::CHANGE_EVENT,cb);
			    }
			}
		      catch(Tango::DevFailed &e)
			{
			  set_state(Tango::FAULT);
			}




extract of the callback (array declaration in DevLong):


  void DoubleEventCallBack::push_event(Tango::EventData *myevent)
  {

    Tango::DevVarLongArray *double_value;

    try
      {
	  if(!myevent->err)
	    {
	      *(myevent->attr_value) >> double_value;
	      delete double_value;
	    }
      }
    catch(int e)
      {
	cout << "DoubleEventCallBack::push_event(): could not extract data!\n";
      }
  }



Is it the good way to do this when i have to subsribe to events on dynamic attributes unknown in advance ?
Thanks for help
rbourtembourg avatar
Reynald
Hi,

In your callback, 
myevent->attr_value->data_type
gives you the type of the received event data (int corresponding to the index of the type in enum CmdArgType type declared in tango_const.h include file).

You can then adapt your code depending on the received type.
Rosenberg's Law: Software is easy to make, except when you want it to do something new.
Corollary: The only software that's worth making is software that does something new.
Edited 6 years ago
rbourtembourg avatar
Reynald
By the way, you should catch Tango::DevFailed exceptions (not int exceptions) in your callback when you try to extract the data.
Rosenberg's Law: Software is easy to make, except when you want it to do something new.
Corollary: The only software that's worth making is software that does something new.
avatar par défaut
JCM


JCM
thanks,
so i adapt my code depending on the received type :)

but still many problems:

1) impossible to compile with the type in enum CmdArgType type declared in tango_const.h include file.
not understood, so put the value smile

2) myevent->attr_value->data_type returns always the same value equal to 2 !
not understood, so passed the data_type at the callback call smile

3) as i have only one callback for all events, i protected with a mutex. However the events are blocked or slowed
down after a while ;( but that's another story … smile

extract of the push_event() method :)


	    try
      {
	  if(!myevent->err)
	    {
	      eventLock.lock();

	      switch(type)
		{
		case 2:
		  Tango::DevVarShortArray *short_value;
		  *(myevent->attr_value) >> short_value;
		  delete short_value;
		  break;
		case 6
		  Tango::DevVarUShortArray *ushort_value;
		  *(myevent->attr_value) >> ushort_value;
		  delete ushort_value;
		  break;
		case 3:
		  Tango::DevVarLongArray *long_value;
		  *(myevent->attr_value) >> long_value;
		  delete long_value;
		  break;
		case 7:
		  Tango::DevVarULongArray *ulong_value;
		  *(myevent->attr_value) >> ulong_value;
		  delete ulong_value;
		  break;
		case 4:
		  Tango::DevVarFloatArray *float_value;
		  *(myevent->attr_value) >> float_value;
		  delete float_value;
		  break;
		case 5:
		  Tango::DevVarDoubleArray *double_value;
		  *(myevent->attr_value) >> double_value;
		  delete double_value;
		  break;
		}	      

	      eventLock.unlock();
	    }
      }
    catch(Tango::DevFailed &e)
      {
	cout << "DoubleEventCallBack::push_event(): could not extract data\n" << endl;
	Tango::Except::print_exception(e);
      }
rbourtembourg avatar
Reynald
JCM
thanks,
so i adapt my code depending on the received type :)

but still many problems:

1) impossible to compile with the type in enum CmdArgType type declared in tango_const.h include file.
not understood, so put the value smile

Did you prefix it with the namespace Tango?
e.g.: Tango::DEV_SHORT ?

JCM
2) myevent->attr_value->data_type returns always the same value equal to 2 !
not understood, so passed the data_type at the callback call smile

The data type is transmitted on the network only since Tango 9 (IDL 5).
Are you subscribing to Tango 8 devices?
Maybe what you are observing is a consequence of the fix of https://github.com/tango-controls/cppTango/issues/248 ?
Rosenberg's Law: Software is easy to make, except when you want it to do something new.
Corollary: The only software that's worth making is software that does something new.
avatar par défaut
JCM
Late answer smile


Reynald
1) impossible to compile with the type in enum CmdArgType type declared in tango_const.h include file.
not understood, so put the value smile



Did you prefix it with the namespace Tango?
e.g.: Tango::DEV_SHORT ?

Not effectively. I'm going to try.



Reynald
2) myevent->attr_value->data_type returns always the same value equal to 2 !
not understood, so passed the data_type at the callback call smile


The data type is transmitted on the network only since Tango 9 (IDL 5).
Are you subscribing to Tango 8 devices?
Maybe what you are observing is a consequence of the fix of https://github.com/tango-controls/cppTango/issues/248 ?

All Tango 9 devices.



Thanks again.
 
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