Re: [tcljava-user] (no subject)

[Martin L. <mar...@gm...>]

Hi Dan,

the reason is, that you return an element from the just built list by
pushing it into the interpreter.

If the method is ending the list object is released and all its elements
will be released, too.
So the result list element won't be present anymore.

In my eyes even a "list.preserve" call wouldn't solve the problem
because it raises the question, when the list would be release again?
I would say ... never!

So I would duplicate the object I want to return!

In C(++) I would do:

    *Tcl_Obj** pList = *Tcl_NewObj*();

    // building the list

    *Tcl_Obj** pElement = NULL;
    *Tcl_ListObjIndex*(pInterp, pList, nIndex, &pElement);
    *Tcl_SetObjResult*(pInterp, *Tcl_DuplicateObj*(pElement));

By the way ... why do you build a tcl list to extract one element and to
forget it?
Why not using Java container objects, if container objects are really
needed?

Ok - I hope my suggestion helps.

Best regards,

Martin Lemburg

Dan Diolosa wrote:
>
> Hi,
>
>
> I am wondering why I need to "preserve" a TclList that I don't return
> to TCL, nor need/use after the function returns.
>
> I am trying to return just one sub-list from a list of sub-lists.   If
> I have just a list of normal TclObjects I can return one item without
> a problem.   What is wrong with this:
>
>  
>
> public void cmdProc(Interp interp, TclObject argv[]) throws TclException
>
>   {
>
>     TclObject list = TclList.newInstance();
>
>  
>
>     //Create the first sublist
>
>     TclObject list1 = TclList.newInstance();
>
>     TclList.append(interp, list1, TclString.newInstance("1.1"));
>
>     TclList.append(interp, list1, TclString.newInstance("1.2"));
>
>  
>
>     //Create the second sublist
>
>     TclObject list2 = TclList.newInstance();
>
>     TclList.append(interp, list2, TclString.newInstance("2.1"));
>
>     TclList.append(interp, list2, TclString.newInstance("2.2"));
>
>  
>
>     //Add to main list
>
>     TclList.append(interp, list, list1);
>
>     TclList.append(interp, list1, list2);
>
>   
>
>     //list.preserve();  
>
>  
>
>     //return just the second sublist list
>
>     interp.setResult(TclList.index(interp, list, 0));
>
>   }
>
>  
>
> When I run it (without the preserve()), I get this:
>
> % ls_test
>
> alloc: invalid block: 009B3DF0: f8 0 0
>
>  
>
> This application has requested the Runtime to terminate it in an
> unusual way.
>
> Please contact the application's support team for more information.
>
> D:\
>
>  
>
>  
>
> When I run a similar situation in my production code I get the error
> from JRE side, SIGSEGV on Linux and ACCESS_VIOLATION on Windows:
>
>  
>
> #
>
> # An unexpected error has been detected by HotSpot Virtual Machine:
>
> #
>
> #  SIGSEGV (0xb) at pc=0x4008eb78, pid=4098, tid=1074768448
>
> #
>
> # Java VM: Java HotSpot(TM) Client VM (1.5.0_06-b05 mixed mode, sharing)
>
> # Problematic frame:
>
> # C  [libtcl8.4.so+0x77b78]
>
> #
>
> # An error report file with more information is saved as
> hs_err_pid4098.log
>
> #
>
> # If you would like to submit a bug report, please visit:
>
> #   http://java.sun.com/webapps/bugreport/crash.jsp
>
> #
>
> Aborted (core dumped)
>
>
> Thanks,
>
> Dan
>
>
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