C# Corrupt Memory Error

Question

I cant post the code (proprietary issues) but does anyone know what types of things would cause the following error in C#. It is being thrown by a VOIP client that I wrote (using counterpath api) when the call is ended by the other client. The error is:

System.AccessViolationException was unhandled
  Message="Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
  Source="System.Windows.Forms"
  StackTrace:
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at CollabAnalysisSF.Edge.GUI.Forms.Program.Main() in d:\data\beyerss\Desktop\client\GUI\ARGui\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

UPDATE:
Turns out one of the libraries we were using was sending off an event that we didnt know about, and the problem was in there somewhere. Fixed now.

Answer 1

List of some possibilities:

• An object is being used after it has been disposed. This can happen a lot if you are disposing managed object in a finalizer (you should not do that).
• An unmannaged implementation of one of the object you are using is bugged and it corrupted the process memory heap. Happens a lot with DirectX, GDI and others.
• Mashaling on managed-unmanaged boundary is flawed. Make sure you pin a managed pointer before you use it on an unmanaged part of code.
• You are using unsafe block and doing funny stuff with it.

---

In you case it could be a problem with Windows Forms. But the problem is not that it is happening, but rather that it is not being reported correctly; you possibly still have done something wrong.

Are you able to determine what control is causing the error using the HWND? Is it always the same? Is this control doing something funny just before the application crashes? Is the unmannaged part of the control a custom window or a standard control?

Answer 2

This kind of prolem can occur if you are calling unmanaged code e.g. a dll. It can occur when Marshalling goes horribly wrong.

Can you tell us if you are calling unmanaged code? If so are you using default Marshalling or more specific stuff? From the looks of the stack trace are you using unsafe code e.g. Pointers and the like? This could be your problem.

Answer 3

Here is a more detailed stacktrace. It looks to me like it has something to do with the System.Windows.Form.dll

the TargetSite is listed as {IntPtr DispatchMessageW(MSG ByRef)}
and under module it has System.windows.forms.dll