Experimental Physics and
Industrial Control System

Hello,

 

I am considering the Channel Access Portable Server for supporting the C++ middle layer servers.

The associated PVs will maintain one-dimensional arrays of characters. Their lengths can be

significant.  So, passing by pointer in read/write methods would be a preferable way. The ‘write’ case

looks straightforward (as described in the tutorial, p.35):

 

class my PV : public casPV {

….

gdd* pValue;

};

 

caStatus myPV::write(const casCtx& ctx, gdd &value){

…

pValue->unreference();

pValue = &value;

pValue->reference();

…

}

 

The ‘read’ case looks trickier (Probably, because it is not explained).

 

In short, CORBA addresses such case by using the additional wrappers, e.g. gdd_var objects,

in the ‘read’ method. However, the signature of this method is already defined by the basis

class casPV. Fortunately, it seems we can still  use the gdd-based approach using another

mechanism, the pv-associated destructor, e.g. myPVReadDestructor:

 

caStatus myPV::read(const casCtx& ctx, gdd &value){

…

value.putRef(pValue->dataPointer(), new myPVReadDestructor(pValue));

pValue->reference();

}

 

where :

 

myPVReadDestructor::run(…){

pValue->unreference();

}

 

Any comments and suggestions about a better solution.

 

Thank you,

Nikolay