_heapwalk reports _HEAPBADNODE, causes breakpoint or loops endlessly
- by Stefan Hubert
I use _heapwalk to gather statistics about the Process' standard heap.
Under certain circumstances i observe unexpected behaviours like:
_HEAPBADNODE is returned
some breakpoint is triggered inside _heapwalk, telling me the heap might got corrupted
access violation inside _heapWalk.
I saw different behaviours on different Computers. On one Windows XP 32 bit machine everything looked fine, whereas on two Windows XP 64 bit machines i saw the mentioned symptoms.
I saw this behaviour only if LowFragmentationHeap was enabled.
I played around a bit.
I walked the heap several times right one after another inside my program. First time doing nothing in between the subsequent calls to _heapWalk (everything fine). Then again, this time doing some stuff (for gathering statistics) in between two subsequent calls to _heapWalk. Depending upon what I did there, I sometimes got the described symptoms.
Here finally a question:
What exactly is safe and what is not safe to do in between two subsequent calls to _heapWalk during a complete heap walk run?
Naturally, i shall not manipulate the heap. Therefore i doublechecked that i don't call new and delete.
However, my observation is that function calls with some parameter passing causes my heap walk run to fail already. I subsequently added function calls and increasing number of parameters passed to these. My feeling was two function calls with two paramters being passed did not work anymore.
However I would like to know why.
Any ideas why this does not happen on some machines?
Any ideas why this only happens if LowFragmentationHeap is enabled?
Sample Code finally:
#include <malloc.h>
void staticMethodB( int a, int b )
{
}
void staticMethodA( int a, int b, int c)
{
staticMethodB( 3, 6);
return;
}
...
_HEAPINFO hinfo;
hinfo._pentry = NULL;
while( ( heapstatus = _heapwalk( &hinfo ) ) == _HEAPOK )
{
//doing nothing here works fine
//however if i call functions here with parameters, this causes
//_HEAPBADNODE or something else
staticMethodA( 3,4,5);
}
switch( heapstatus )
{
...
case _HEAPBADNODE:
assert( false );
/*ERROR - bad node in heap */
break;
...
