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PODebug Win32 application hang
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  1. PODebug Win32 application hang
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    copied!<p>I'm having trouble finding the cause for a hang in a Win32 application. The software renders some data to an OpenGL visual in a tight loop:</p> <pre><code>std::vector&lt;uint8_t&gt; indices; glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(2, GL_DOUBLE, 0, vertexDataBuffer); while (...) { // get index type (1, 2, 4) and index count indices.resize(indexType * count); // get indices into "indices" buffer getIndices(indices.data(), indices.size()); //&lt; seems to hang here! // draw (I'm using the correct parameters) glDrawElements(GL_TRIANGLES_*, count, GL_UNSIGNED_*); } glDisableClientState(GL_VERTEX_ARRAY); </code></pre> <p>The code is compiled using VC11 Update 1 (CTP 3). When running the optimized binary, it hangs inside the call to <code>getIndices()</code> (more about this below) after a few of those loops. I already have...</p> <ul> <li>triple validated all buffers, even appended CRCs to make sure I'm not having any buffer overruns</li> <li>Added a call to <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366708%28v=vs.85%29.aspx" rel="nofollow">HeapValidate()</a> inside the loop to ensure the heap is not corrupt</li> <li>used ApplicationVerifier</li> <li>Enabled heap allocation monitoring using <a href="http://msdn.microsoft.com/en-us/library/ff549561.aspx" rel="nofollow">GFlags and PageHeap</a>.</li> <li>broke into WinDbg when the application locks up</li> </ul> <p>I did <strong>not</strong> find any problems with the code accessing the allocated buffer, nor any heap corruption. However, if I disable the <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366750%28v=vs.85%29.aspx" rel="nofollow">low-fragmentation heap</a>, the issue vanishes. It also vanishes, if I use a separate (low-fragmentation) heap for the <code>indices</code> buffer.</p> <p>Anyway, here is the stack trace leading to the dead-lock:</p> <pre><code>0:000&gt; kb ChildEBP RetAddr Args to Child 0034e328 77b039c3 00000000 0034e350 00000000 ntdll!ZwWaitForKeyedEvent+0x15 0034e394 77b062bc 77b94724 080d36a8 0034e464 ntdll!RtlAcquireSRWLockExclusive+0x12e 0034e3c0 77aeb652 0034e464 0034e4b4 00000000 ntdll!RtlpCallVectoredHandlers+0x58 0034e3d4 77aeb314 0034e464 0034e4b4 77b94724 ntdll!RtlCallVectoredExceptionHandlers+0x12 0034e44c 77aa0133 0034e464 0034e4b4 0034e464 ntdll!RtlDispatchException+0x19 0034e44c 77b062c5 0034e464 0034e4b4 0034e464 ntdll!KiUserExceptionDispatcher+0xf 0034e7bc 77aeb652 0034e860 0034e8b0 00000000 ntdll!RtlpCallVectoredHandlers+0x61 0034e7d0 77aeb314 0034e860 0034e8b0 0034ec28 ntdll!RtlCallVectoredExceptionHandlers+0x12 0034e848 77aa0133 0034e860 0034e8b0 0034e860 ntdll!RtlDispatchException+0x19 0034e848 1c43c666 0034e860 0034e8b0 0034e860 ntdll!KiUserExceptionDispatcher+0xf 0034ebe8 1c43c4e5 0034ec28 080d35d0 080d35d6 lcdb4!lc::db::PackedIndices::unpackIndices&lt;unsigned char&gt;+0x86 0034ec14 1c45922d 0034ec28 080d35d0 00000006 lcdb4!lc::db::PackedIndices::unpack+0xb5 ... xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx xxxxxxxx getIndices </code></pre> <p>For completeness, I posted the code of <code>lc::db::PackedIndices::unpackIndices()</code>, including all code added for debugging, to <a href="http://ideone.com/sVVXX7" rel="nofollow">http://ideone.com/sVVXX7</a>.</p> <p>The code triggering the call to <code>KiUserExceptionDispatcher</code> is <code>(*p++) = static_cast&lt;T&gt;(index);</code> (<code>mov dword ptr [esp+10h],eax</code>).</p> <p>I just can't seem to figure out what's going on. An exception seems to have been thrown, but none of my exception handlers are called. The application just hangs. I checked for any deadlocked critical sections (<code>!lock</code>) but found none. Furthermore, I don't see why an exception should be raised, as the memory locations are all valid. Could anyone give me some hints?</p> <h2>Update</h2> <p>I tried to find the type of exception being thrown:</p> <pre><code>0:000&gt; s -d esp L1000 1003f 0028ebdc 0001003f 00000000 00000000 00000000 ?............... 0028efd8 0001003f 00000000 00000000 00000000 ?............... 0:000&gt; .cxr 0028ebdc eax=77b94724 ebx=0804be30 ecx=00000002 edx=00000004 esi=77b94724 edi=0804be28 eip=77b062c5 esp=0028eec4 ebp=0028eee4 iopl=0 nv up ei ng nz na pe cy cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010287 ntdll!RtlpCallVectoredHandlers+0x61: 77b062c5 ff03 inc dword ptr [ebx] ds:002b:0804be30=00000001 0:000&gt; .cxr 0028efd8 eax=0000003b ebx=00000001 ecx=0804bd98 edx=0028f340 esi=0028f340 edi=04b77580 eip=1c43c296 esp=0028f2c0 ebp=0028f2fc iopl=0 nv up ei pl nz na po nc cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202 lcdb4!lc::db::PackedIndices::unpackIndices&lt;unsigned char&gt;+0x36: 1c43c296 8801 mov byte ptr [ecx],al ds:002b:0804bd98=3e </code></pre>
 

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