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;
...