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Question

In the following bit of code I’m using C# function pointers to omit using a delegate type, for faster performance. The code works fine when I use a delegate type marshalled as a function pointer, no exception no issues. However when changing it from a delegate to a function pointer it sometimes throws an access violation.

Code is modified to remove namespaces and prefixes not relevant to the question

public static class Engine
{
    // Causing issues with sometimes throwing access violation
    [DllImport("engine", CallingConvention = CallingConvention.Cdecl)]
    public static unsafe extern UInt32 EventScheduler_ScheduleLocalEvent(
        int priority, UInt64 delay, delegate* unmanaged[Cdecl]<nint, void> callback, nint obj);

    // Works fine every time, but is much slower seems due to delegate instatiations
    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
    public delegate void EventScheduler_ScheduleLocalEvent_callbackDelegate(IntPtr obj);
    [DllImport("engine", CallingConvention = CallingConvention.Cdecl)]
    public static unsafe extern UInt32 EventScheduler_ScheduleLocalEvent(
        int priority,
        UInt64 delay,
        [MarshalAs(UnmanagedType.FunctionPtr)] EventScheduler_ScheduleLocalEvent_callbackDelegate callback,
        IntPtr obj);

}

public static class EventScheduler
{
    public delegate void EventCallback();

    // attribute is only present in the function pointer senario
    [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvCdecl ) }, EntryPoint = "ScheduleLocalEvent_EventCallbackFunction")]
    private static void ScheduleLocalEvent_EventCallbackFunction(nint handlePtr)
    {
        Thread.BeginThreadAffinity();
        GCHandle handle = GCHandle.FromIntPtr(handlePtr);
        var cb          = (EventScheduler.EventCallback)handle.Target!;
        cb();
        handle.Free();
        Thread.EndThreadAffinity();
    }
    public static UInt32 ScheduleLocalEvent(int priority, SimulationTime delayTime, EventCallback eventCallback)
    {
        GCHandle handle  = GCHandle.Alloc(eventCallback, GCHandleType.Normal);
        IntPtr handlePtr = GCHandle.ToIntPtr(handle);
        unsafe
        {
            return Engine.EventScheduler_ScheduleLocalEvent(
                priority, delayTime, &ScheduleLocalEvent_EventCallbackFunction, handlePtr);
        }
    }

}

On the C++ side

#define API extern "C" __declspec(dllexport)

API uint32_t EventScheduler_ScheduleLocalEvent(int priority, uint64_t delay, void(__cdecl* callback)(void* obj), void* obj)
{
    ERSAssert(Ers::Core::InsideSubModel());
    Core::SyncManagerBase& syncManager = Ers::Core::GetSyncManagerBase();
    return syncManager.ScheduleEvent(priority, delay, [callback, obj]() { callback(obj); });
}

The folowing output is given when the program is ran.

AWealthOfRows.exe (process 39016) exited with code -1073741819.

With the following output

' AWealthOfRows.exe' (Win32): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0AWealthOfRows.exe'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32ntdll.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32kernel32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32KernelBase.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32user32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32win32u.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32gdi32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32gdi32full.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32msvcp_win.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32ucrtbase.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32shell32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32advapi32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32msvcrt.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32sechost.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32bcrypt.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32rpcrt4.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32imm32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program Filesdotnethostfxr9.0.0-preview.3.24172.9hostfxr.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5hostpolicy.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5coreclr.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32ole32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32combase.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32oleaut32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32bcryptprimitives.dll'. The thread 41728 has exited with code 0 (0x0). 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Private.CoreLib.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5clrjit.dll'. 'AWealthOfRows.exe' (CoreCLR: DefaultDomain): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Private.CoreLib.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32kernel.appcore.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0AWealthOfRows.dll'. The thread 41464 has exited with code 0 (0x0). 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0AWealthOfRows.dll'. Symbols loaded. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32icu.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesMicrosoft Visual Studio2022CommunityCommon7IDECommonExtensionsMicrosoftHotReloadMicrosoft.Extensions.DotNetDeltaApplier.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'c:program filesmicrosoft visual studio2022communitycommon7idecommonextensionsmicrosofthotreloadMicrosoft.Extensions.DotNetDeltaApplier.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.IO.Pipes.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.IO.Pipes.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Linq.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Linq.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Collections.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Collections.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Console.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Console.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.InteropServices.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.InteropServices.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.Overlapped.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.Overlapped.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.AccessControl.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.AccessControl.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.Principal.Windows.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.Principal.Windows.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32ntmarta.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.Claims.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Security.Claims.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.Loader.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Runtime.Loader.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0Ers.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Collections.Concurrent.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0Ers.dll'. Symbols loaded. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Collections.Concurrent.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:ProjectsTestingEnterprise_Resource_SimulatorbindingsCSharpAWealthOfRowsbinDebugnet8.0ers-engine.dll'. Symbols loaded. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32setupapi.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32winmm.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32version.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32vcruntime140d.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32msvcp140d.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32vcruntime140_1d.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32ucrtbased.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:WindowsSystem32cfgmgr32.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Diagnostics.Process.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Diagnostics.Process.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.ComponentModel.Primitives.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.ComponentModel.Primitives.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Memory.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Memory.dll'. 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Text.Encoding.Extensions.dll'. The thread 20540 has exited with code 0 (0x0). The thread 23312 has exited with code 0 (0x0). 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Text.Encoding.Extensions.dll'. The thread 9224 has exited with code 0 (0x0). 'AWealthOfRows.exe' (Win32): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.Thread.dll'. 'AWealthOfRows.exe' (CoreCLR: clrhost): Loaded 'C:Program FilesdotnetsharedMicrosoft.NETCore.App8.0.5System.Threading.Thread.dll'. Exception thrown at 0x000001F303570860 in AWealthOfRows.exe: 0xC0000005: Access violation reading location 0x000001F30385FB32. The Common Language Runtime cannot stop at this exception. Common causes include: incorrect COM interop marshalling and memory corruption. To investigate further use native-only debugging. Unhandled exception at 0x000001F303570860 in AWealthOfRows.exe: 0xC0000005: Access violation reading location 0x000001F30385FB32. The Common Language Runtime cannot stop at this exception. Common causes include: incorrect COM interop marshalling and memory corruption. To investigate further use native-only debugging. The thread '.NET Counter Poller' (35516) has exited with code 3221225477 (0xc0000005). The thread '.NET TP Gate' (24688) has exited with code 3221225477 (0xc0000005). The thread 33416 has exited with code 3221225477 (0xc0000005). The thread '.NET Finalizer' (38504) has exited with code 3221225477 (0xc0000005). The thread '.NET EventPipe' (23352) has exited with code 3221225477 (0xc0000005). The thread 36944 has exited with code 3221225477 (0xc0000005). The thread 30968 has exited with code 3221225477 (0xc0000005). The thread 3560 has exited with code 3221225477 (0xc0000005). The thread 41012 has exited with code 3221225477 (0xc0000005). The thread 13568 has exited with code 3221225477 (0xc0000005). The thread 22992 has exited with code 3221225477 (0xc0000005). The thread '.NET TP Worker' (38436) has exited with code 3221225477 (0xc0000005). The thread 41284 has exited with code 3221225477 (0xc0000005). The thread 40972 has exited with code 3221225477 (0xc0000005). The thread 40980 has exited with code 3221225477 (0xc0000005). The thread 41972 has exited with code 3221225477 (0xc0000005). The thread 39600 has exited with code 3221225477 (0xc0000005). The thread 41096 has exited with code 3221225477 (0xc0000005). The thread 41968 has exited with code 3221225477 (0xc0000005). The thread 7472 has exited with code 3221225477 (0xc0000005). The thread '.NET ThreadPool IO' (36056) has exited with code 3221225477 (0xc0000005). The thread 16184 has exited with code 3221225477 (0xc0000005). The thread 11736 has exited with code 3221225477 (0xc0000005). The thread '.NET TP Worker' (33156) has exited with code 3221225477 (0xc0000005). The thread '.NET TP Worker' (5368) has exited with code 3221225477 (0xc0000005). The thread '.NET ThreadPool IO' (22304) has exited with code 3221225477 (0xc0000005). The thread '.NET TP Worker' (42112) has exited with code 3221225477 (0xc0000005). The thread 40516 has exited with code 3221225477 (0xc0000005). The thread '.NET Tiered Compilation Worker' (2424) has exited with code 3221225477 (0xc0000005). The program '[39016] AWealthOfRows.exe' has exited with code 3221225477 (0xc0000005) 'Access violation'.

I have tried debugging, but when the issue occurs. In which case C++ calls the callback, but before it entering the function’s scope the exception is thrown, but immediately returns with an error code.

For sake of debugging I’ve tried switching the calling convention from cdecl to stdcall to see if it has to do with stack corruption.

My assumptions are that:

static functions marked with [UnmanagedCallersOnly] have a static address, especially when an entrypoint is defined.
Thread.BeginThreadAffinity() followed by Thread.EndThreadAffinity() ensure that an unmanaged thread can sucessfully start excuting managed code.

Good to know:

The function is being invoked by a thread not created in C#, there are many threads calling this function

Looking at the documentation for function pointers here I can’t seem to figure out if I am not following the standard or if there is just an issue with C#’s implementation.

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Danh mục

C# function pointers causes access violation upon calling from C++