Re: [gobo-eiffel-develop] Memory leak with cursors and data structures

[Paul B. [ES] <pa...@ei...>]

I did subscribe but I didn't search the entire newsgroup, my apologies. 

The reason I do not code a loop as suggested is because with heavy
loaded list this would be inefficient because the whole loop has to be
processed.

Paul.

On Tue, 2008-08-12 at 08:40 +0200, Eric Bezault wrote:
> Paul Bates wrote:
> > We've detected a memory leak when using gobo data structure cursors that 
> > do not run to the end, and currently there is no way to clean them up 
> > nicely.
> > 
> > Take the following code
> > 
> > f (a_list: !DS_LINEAR [?ANY])
> >    local
> >      l_cursor: DS_LINEAR_CURSOR [?ANY]
> >      l_stop: BOOLEAN
> >    do
> >      l_cursor := a_list.cursor
> >      from l_cursor.start until l_cursor.after or l_stop loop
> >        l_stop := l_cursor.item = Void
> >        if not l_stop then
> >          l_cursor.forth
> >        end
> >      end
> >    end
> > 
> > Passing a linear structure to 'f' where any item is Void will cause the 
> > leak because the list never goes 'off'. We cannot call 
> > DS_TRAVERSABLE.remove_traversing_cursor and it is not a good idea to do 
> > so because it may have not been added the the managed list or cursors, 
> > given the current lazy-eval implementation.
> > 
> > The current solution is to run out the cursor in another loop or run out 
> > the cursor in the original loop but conditionally process the loop's 
> > functional body. Neither of which look that nice.
> 
> You "discovered" something that is not new:
> 
>    http://www.gobosoft.com/eiffel/gobo/structure/traversal.html
> 
> Look at the red comment. Why don't you write your code like this:
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> f (a_list: !DS_LINEAR [?ANY])
>     local
>       l_cursor: DS_LINEAR_CURSOR [?ANY]
>     do
>       l_cursor := a_list.cursor
>       from l_cursor.start until l_cursor.after loop
>         if l_cursor.item = Void then
>           ... do something interesting here ...
>           l_cursor.go_after
>         else
>           l_cursor.forth
>         end
>       end
>     end
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> as suggested in the doc? Note that `go_after' is a routine that
> I miss very much in the EiffelBase containers.
> 
> 
> PS: Please subscribe to the mailing list before posting.
> 
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