Improve adding container to the container factory

[fuhlig1]

Add a function to add a container to the factory that also checks if the
container already exist. If the container already exist it is not added
again and kFALSE is returned. Otherwise it is added and kTRUE is returned.
The "normal" way to add containers is to use the TList data member directly
which will not report any errors when adding the container. Only when the
destructor of the runtime database is called one will see an error message

Error in TList::Delete: A list is accessing an object (0x55d2e2220550)
already deleted (list name = TList)

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Checklist:

• Rebased against dev branch
• My name is in the resp. CONTRIBUTORS/AUTHORS file
• Followed the seven rules of great commit messages

[fuhlig1]

Could you please check and merge.

[dennisklein]

The need for this kind of checking add function is very worrisome. What does a return value kFALSE mean? It tells the caller that he is not the owner of the object (because the FairContFact instance is). But how can this be in the first place? The caller should already know this.

[fuhlig1]

The need for this kind of checking add function is very worrisome. What does a return value kFALSE mean? It tells the caller that he is not the owner of the object (because the FairContFact instance is). But how can this be in the first place? The caller should already know this.

This only tells the caller that the framework could not add the object to the internal TList because an object with the same name already exist in the list. This is completely independent from the question who is the owner.

The current way which is used all over the place in FairRoot and any derrived project is directly access the Internal TList (which is public) and call TList->Add directly. This works since years until you do a stupid copy and paste error. To use internal data members is a very bad idea but since the code is heavily used we can' change it without breaking all existing code.

I agree that passing the raw pointer is not the desired way. Since the function is not used anywhere yet I will try to implement a proper interface.

[dennisklein]

This only tells the caller that the framework could not add the object to the internal TList because an object with the same name already exist in the list.

True. Still, if it is possible that your calling code tries to add the same object (not by name but by reference) twice to the TList (doesn't matter whether it is through FairContFact or directly on the TList member), it means that the calling code seems to have lost track whether it is the owner of the added object.

root [0] TList* l = new TList; // non-owning container
root [1] TObject* obj = new TObject; // caller owns obj
root [2] l->Add(obj); // caller owns obj
root [3] l->Add(obj); // caller owns obj
root [4] delete l; // fine
root [5]
root [5] l = new TList;
root [6] l->SetOwner(kTRUE); // l now owning container
root [7] l->Add(obj); // caller does not own obj any more
root [8] l->Add(obj); // caller knows it should not call Add any more, because obj holds a non-owning pointer
root [9] delete l;
Error in <TList::Delete>: A list is accessing an object (0x5632af764490) already deleted (list name = TList)

I do not object this PR, especially if you intend to have a TList that actually represents a unique set of TObjects by name. From your issue description I got the impression you wanted to fix a double add of the same object (by reference), which would indicate a problem in the calling code.

[dennisklein]

I added the comment to the new interface.