Re: Memory Leak in Array<T> class

[David Bateman]

According to John W. Eaton <address@hidden> (on 11/01/04):
> If this code caused a memory leak, then running the above in a loop
> like this:
> 
>   page_screen_output = 0;
>   while (1)
>     foo;
>   endwhile
> 
> or, to speed things up a bit, modifying it to be
> 
>   #include <octave/config.h>
>   #include <octave/oct.h>
> 
>   DEFUN_DLD (xxx, args, , " ")
>   {
>     NDArray a;
>     return octave_value ();
>   }
> 
> and running the same loop would cause Octave to grow without bound
> (even if the growth was slow).  But that is not what I see.
> 
> The key is the definition of the nil_rep function:
> 
>   typename Array<T>::ArrayRep *nil_rep (void) const
>     {
>       static typename Array<T>::ArrayRep *nr
>       = new typename Array<T>::ArrayRep ();
> 
>       return nr;
>     }
> 
> Note that the returned value is static within the function, so it is
> constructed just once, when NR is initialized.  Each time nil_rep is
> called, we return the same empty ArrayRep object.  It is correct to
> increment the reference count for this object in the constructors,
> because we never want the static NR object to be destroyed.  Defining
> nil_rep this way is an attempt to speed things up by avoiding
> unnecessary calls to new and delete to repeatedly create an empty
> ArrayRep object.  Since all empty ArrayRep objects have the same
> representation, we should only have to create it once.


Amazing what a difference a single "static" keyword makes in this
case. I'd missed that...

Cheers
David

-- 
David Bateman                                address@hidden
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