Re: reference counting

[James W. W. <ja...@wr...>]

Joseph J. Strout" <jo...@st...> wrote:

>Please check my text on reference counting (below)... I want to make 
>sure I don't lead anyone astray.
>

>When that reference is about to disappear -- for example, because
>it's in a local variable that is about to go out of scope or be
>assigned a different value, or in an object that is being destroyed
>-- then you must call Q3Object_Dispose to let Quesa know that there
>is one less reference to that object.

The first use of the word "object" here refers, I assume, to 
something like a C++ object, while the last use refer to a Quesa 
object.  This may cause confusion.  If a reference is held by a Quesa 
object, such as a group, then it is Quesa's responsibility to dispose 
the reference when the object is destroyed.

>Assuming this is all correct, the reader will be wondering: Why do
>Dispose a Q3Object, but I can only GetReference to a Q3SharedObject?
>It doesn't seem very parallel.

This does not bother me, though maybe I'm just used to it.  For 
shared objects, "dispose" has a special meaning.

>  And, is it safe to call Q3SharedObject

You mean Q3Shared_GetReference?

>  on something that is not, in fact, a Q3SharedObject

If we look at the source code in Quesa, we see that 
Q3Shared_GetReference will have an assertion failure and then return 
NULL.

>(and what's an example of a Q3Object like that)?

Look at the typedefs of TQ3SharedObject etc. in Quesa.h, and you see 
that views and picks are examples of non-shared Quesa objects.
-- 
   James W. Walker, ScriptPerfection Enterprises, Inc.
   <http://www.write-brain.com/>