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POAccess violation in code that is not mine
 

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    <p>I'm not sure how to go about debugging this. I have a C# program consisting entirely of managed code, running in .NET 4.5. After running it for a while, at some seemingly random time, I get a an error "An unhandled exception of type 'System.AccessViolationException' occurred in mscorlib.dll". Since I'm running it from Visual Studio (2012) I click "break" and am presented with the following call stack:</p> <pre><code>mscorlib.dll!System.Threading._IOCompletionCallback.PerformIOCompletionCallback(uint errorCode, uint numBytes, System.Threading.NativeOverlapped* pOVERLAP) + 0x47 bytes [Native to Managed Transition] ntdll.dll!_NtRequestWaitReplyPort@12() + 0xc bytes kernel32.dll!_ConsoleClientCallServer@16() + 0x4f bytes kernel32.dll!_GetConsoleLangId@4() + 0x2b bytes kernel32.dll!_SetTEBLangID@0() + 0xf bytes KernelBase.dll!_GetModuleHandleForUnicodeString@4() + 0x22 bytes mdnsNSP.dll!7177aa48() [Frames below may be incorrect and/or missing, no symbols loaded for mdnsNSP.dll] mdnsNSP.dll!71775b06() mdnsNSP.dll!71774ded() mdnsNSP.dll!71774e8c() bcryptprimitives.dll!746d1159() bcryptprimitives.dll!746d1137() ntdll.dll!_LdrpCallInitRoutine@16() + 0x14 bytes ntdll.dll!_NtTestAlert@0() + 0xc bytes ntdll.dll!_NtContinue@8() + 0xc bytes ntdll.dll!_LdrInitializeThunk@8() + 0x1a bytes </code></pre> <p>An interesting thing I notice is that nothing in the call stack is my code. </p> <p>What strategy would you advise I use to find the route of the problem? Or have you seen a problem similar to this and have any tips?</p> <p>Since the exception doesn't seem to include my code, I don't know what information to include that would be helpful in answering the question, but ask me if there is anything else that I should include. </p> <p>Since the error may be IO related (since PerformIOCompletionCallback is at the top of the stack), this is a list of typical IO tasks that this application performs:</p> <ul> <li>TcpListener.AcceptTcpClientAsync </li> <li>NetworkStream.Write/BeginRead/EndRead</li> <li>SqlCommand.BeginExecuteReader/EndExecuteReader</li> <li>StreamWriter.WriteLine</li> </ul> <p>Other notes:</p> <ul> <li>It seems to be roughly repeatable - I get the same error in the same place (PerformIOCompletionCallback), but have to wait a different length of time to get it (in the order of minutes). </li> <li>I don't think I can manufacture a small program that reliably highlights the problem. My program handles many thousands of similar IO operations before it hits this error.</li> </ul> <p><strong>Edit:</strong></p> <p>Based on the suggestion by @Kevin that Mdnsnsp.dll is from Bonjour, I uninstalled Bonjour and tried again. The exception persists, but the call stack is much cleaner:</p> <pre><code>mscorlib.dll!System.Threading._IOCompletionCallback.PerformIOCompletionCallback(uint errorCode, uint numBytes, System.Threading.NativeOverlapped* pOVERLAP) + 0x47 bytes [Native to Managed Transition] kernel32.dll!@BaseThreadInitThunk@12() + 0x12 bytes ntdll.dll!___RtlUserThreadStart@8() + 0x27 bytes ntdll.dll!__RtlUserThreadStart@8() + 0x1b bytes </code></pre> <p>I'm assuming the Bonjour installer installed some benign hook DLL for network traffic, but uninstalling it did not fix the problem.</p> <p><strong>Edit:</strong></p> <p>I have temporarily re-coded all my <code>unsafe</code> functions using slower "safe" equivalents to eliminate that as a suspect. Now none of the assemblies in the application are compiled using unsafe switch. The problem still persists. To reiterate, I now have no unsafe code, no native code and no P/Invoke calls (in user code) in this application, but I am still experiencing the <code>AccessViolationException</code> as described above.</p>
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    1. CODo you happen to have the /3GB switch enabled in the boot.ini? I remember getting strange errors like this on a system I worked upon. I came to the conclusion the process was running out of resources handling I/O because of the reduced memory available to it.
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    2. COAre you using any `unsafe` code or P/Invoke? | Such an error would fit with the GC moving some buffer the native code still needs.
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    3. COThe exception might be thrown by unmanaged code that your managed code is calling. [Enable unmanaged code debugging](http://msdn.microsoft.com/en-us/library/vstudio/tdw0c6sf%28v=vs.100%29.aspx) in your solution and then trying debugging your program.
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