I need to pass a managed callback to an unmanaged TCP receiver. Since its a thread that needs to exist for the lifetime of the application, I need to prevent it from getting garbage collected. I have read everywhere that pinning function pointers is not required and the GCHandle.Alloc will do the job of preventing garbage collection. But is this a given? I have seen that the AppPool hosting this code crashes with an access violation. Why should I not suspect the fact that this error occurs because the function pointer was garbage collected? Why does pinning the pointer as below reduce the number of crashes?

typedef void (__cdecl *ProcMessageFunc)(void* param, void* paramBuf, ULONG bufSize);
FuncDelegate^ fp = gcnew MessageFuncDelegate(this, &Handler);
pin_ptr<MessageFuncDelegate^> pinnedFunctionPointer = &fp;
ret = Receiver ((ProcMessageFunc)pinnedFunctionPointer);