[Harbour] Error(2) BASE/1301 Object destructor failure: Reference to freed block

[Szakáts Viktor]

Thanks Przemek. I'll keep an open eye, my C code is
now really bare bones (and only 100K) and reviewed
to death, but maybe there's something in it still.
Will try to collect more info and review along your
suggestions.

Brgds,
Viktor

On 2009.05.11., at 20:52, Przemyslaw Czerpak wrote:

> On Mon, 11 May 2009, Szak�ts Viktor wrote:
>
> Hi,
>
>> I just received this error in my otherwise stable app:
>> Error(2) BASE/1301 Object destructor failure: Reference to freed  
>> block
>> Then it gave an MSVC RTL error message, finally a
>> regular app crash (but without logs).
>> This happened with an MSVC 2005 build, rev 10222, in
>> an hb_idleSleep() call, after leaving the app running for
>> hours, most of the time idling with a screen saver and
>> playing with it for a few minutes. The error happened
>> when trying to exit to idle app. This also means I cannot
>> create a small example to replicate the error.
>> Is there anything I can do to track this down, or other
>> ideas why could this happen?
>> [ The app uses some private C code, but only simple
>> function calls and it also does some GC collected
>> allocations in gauge/file viewer functionality. ]
>
> hb_idleSleep() can activate the GC so it can be shown in call stack
> but the problem is not in this function but somewhere else, probably
> in your local code but I can only guess. Harbour counts all GC  
> allocations
> and deallocations and if they are not equal or when destructor  
> reattach
> destroyed block to known item which is not destroyed in the same pass
> then above RT error message is generated.
> It can be caused by stupid typo like dummy hb_gcAlloc() call without
> attaching the result to know for HVM HB_ITEM, f.e.:
>
>   proc main()
>      f()
>      hb_idleReset(); hb_idleSleep(1)
>   return
>   #pragma begindump
>   #include "hbapi.h"
>   HB_FUNC_STATIC( F ) { hb_gcAlloc( 10, NULL ); }
>   #pragma enddump
>
> or it can be sth more serious like result of some memory corruption,  
> f.e.:
>
>   proc main()
>      f( {} )
>      hb_idleReset(); hb_idleSleep(1)
>   return
>   #pragma begindump
>   #include "hbapi.h"
>   HB_FUNC_STATIC( F )
>   {
>      PHB_ITEM pItem = hb_param( 1, HB_IT_ANY );
>      /* simulate memory corruption */
>      memset( pItem, 0, 4 );
>   }
>   #pragma enddump
>
>
> What exactly happen in you case I do not know. I can only tell you  
> that
> one memory blocks allocated by hb_gcAlloc():
>   1. was not attached to know item at all
> or:
>   2. it was reused and attached to new item after destroy  
> (hb_gcFree())
> or:
>   3. the reference counter to such memory block (or item which kept  
> such
>      reference counter) had been corrupted (overwritten) by some  
> buggy code.
>
> best regards,
> Przemek
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