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PO_heapwalk reports _HEAPBADNODE, causes breakpoint or loops endlessly
 

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  1. PO_heapwalk reports _HEAPBADNODE, causes breakpoint or loops endlessly
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    <p>I use _heapwalk to gather statistics about the Process' standard heap.</p> <p>Under certain circumstances i observe unexpected behaviours like:</p> <ul> <li>_HEAPBADNODE is returned</li> <li>some breakpoint is triggered inside _heapwalk, telling me the heap might got corrupted</li> <li>access violation inside _heapWalk.</li> </ul> <p>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.</p> <p>I saw this behaviour only if LowFragmentationHeap was enabled.</p> <p>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.</p> <p>Here finally a question:</p> <p>What exactly is safe and what is not safe to do in between two subsequent calls to _heapWalk during a complete heap walk run?</p> <p>Naturally, i shall not manipulate the heap. Therefore i doublechecked that i don't call <code>new</code> and <code>delete</code>. 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.</p> <p>However I would like to know why. Any ideas why this does <em>not</em> happen on some machines? Any ideas why this only happens if LowFragmentationHeap is enabled?</p> <p>Sample Code finally:</p> <blockquote> <p><code>#include &lt;malloc.h&gt; </p> <p>void staticMethodB( int a, int b )<br> {<br> } </p> <p>void staticMethodA( int a, int b, int c)<br> {<br> staticMethodB( 3, 6);<br> return;<br> } </p> <p>... </p> <p>_HEAPINFO hinfo;<br> hinfo._pentry = NULL;<br> while( ( heapstatus = _heapwalk( &amp;hinfo ) ) == _HEAPOK )<br> { </p> <pre><code>//doing nothing here works fine //however if i call functions here with parameters, this causes //_HEAPBADNODE or something else staticMethodA( 3,4,5); </code></pre> <p>}<br> switch( heapstatus )<br> {<br> ...<br> case _HEAPBADNODE:<br> assert( false );<br> /*ERROR - bad node in heap */<br> break;<br> ... </code></p> </blockquote>
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