如何使 .NET COM 对象成为单元线程？

Question

.NET 对象默认是自由线程的。如果通过 COM 编组到另一个线程，它们总是被编组到自己，无论创建者线程是否是 STA，也不管它们的 ThreadingModel 注册表值。我怀疑，他们汇总了 Free Threaded Marshaler (more details about COM threading could be found here).

我想让我的 .NET COM 对象在编组到另一个线程时使用标准的 COM 编组器代理。问题：

using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Threading;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            var apt1 = new WpfApartment();
            var apt2 = new WpfApartment();

            apt1.Invoke(() =>
            {
                var comObj = new ComObject();
                comObj.Test();

                IntPtr pStm;
                NativeMethods.CoMarshalInterThreadInterfaceInStream(NativeMethods.IID_IUnknown, comObj, out pStm);

                apt2.Invoke(() =>
                {
                    object unk;
                    NativeMethods.CoGetInterfaceAndReleaseStream(pStm, NativeMethods.IID_IUnknown, out unk);

                    Console.WriteLine(new { equal = Object.ReferenceEquals(comObj, unk) });

                    var marshaledComObj = (IComObject)unk;
                    marshaledComObj.Test();
                });
            });

            Console.ReadLine();
        }
    }

    // ComObject
    [ComVisible(true)]
    [Guid("00020400-0000-0000-C000-000000000046")] // IID_IDispatch
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    public interface IComObject
    {
        void Test();
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    [ComDefaultInterface(typeof(IComObject))]
    public class ComObject : IComObject
    {
        // IComObject methods
        public void Test()
        {
            Console.WriteLine(new { Environment.CurrentManagedThreadId });
        }
    }


    // WpfApartment - a WPF Dispatcher Thread 
    internal class WpfApartment : IDisposable
    {
        Thread _thread; // the STA thread
        public System.Threading.Tasks.TaskScheduler TaskScheduler { get; private set; }

        public WpfApartment()
        {
            var tcs = new TaskCompletionSource<System.Threading.Tasks.TaskScheduler>();

            // start the STA thread with WPF Dispatcher
            _thread = new Thread(_ =>
            {
                NativeMethods.OleInitialize(IntPtr.Zero);
                try
                {
                    // post a callback to get the TaskScheduler
                    Dispatcher.CurrentDispatcher.InvokeAsync(
                        () => tcs.SetResult(System.Threading.Tasks.TaskScheduler.FromCurrentSynchronizationContext()),
                        DispatcherPriority.ApplicationIdle);

                    // run the WPF Dispatcher message loop
                    Dispatcher.Run();
                }
                finally
                {
                    NativeMethods.OleUninitialize();
                }
            });

            _thread.SetApartmentState(ApartmentState.STA);
            _thread.IsBackground = true;
            _thread.Start();
            this.TaskScheduler = tcs.Task.Result;
        }

        // shutdown the STA thread
        public void Dispose()
        {
            if (_thread != null && _thread.IsAlive)
            {
                InvokeAsync(() => System.Windows.Threading.Dispatcher.ExitAllFrames());
                _thread.Join();
                _thread = null;
            }
        }

        // Task.Factory.StartNew wrappers
        public Task InvokeAsync(Action action)
        {
            return Task.Factory.StartNew(action,
                CancellationToken.None, TaskCreationOptions.None, this.TaskScheduler);
        }

        public void Invoke(Action action)
        {
            InvokeAsync(action).Wait();
        }
    }

    public static class NativeMethods
    {
        public static readonly Guid IID_IUnknown = new Guid("00000000-0000-0000-C000-000000000046");
        public static readonly Guid IID_IDispatch = new Guid("00020400-0000-0000-C000-000000000046");

        [DllImport("ole32.dll", PreserveSig = false)]
        public static extern void CoMarshalInterThreadInterfaceInStream(
            [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid,
            [MarshalAs(UnmanagedType.IUnknown)] object pUnk,
            out IntPtr ppStm);

        [DllImport("ole32.dll", PreserveSig = false)]
        public static extern void CoGetInterfaceAndReleaseStream(
            IntPtr pStm,
            [In, MarshalAs(UnmanagedType.LPStruct)] Guid riid,
            [MarshalAs(UnmanagedType.IUnknown)] out object ppv);

        [DllImport("ole32.dll", PreserveSig = false)]
        public static extern void OleInitialize(IntPtr pvReserved);

        [DllImport("ole32.dll", PreserveSig = true)]
        public static extern void OleUninitialize();
    }
}

输出：

{ CurrentManagedThreadId = 11 }
{ 等于 = 真 }
{ CurrentManagedThreadId = 12 }

注意我使用 CoMarshalInterThreadInterfaceInStream/CoGetInterfaceAndReleaseStream 将 ComObject 从一个 STA 线程编组到另一个。 我希望在同一个原始线程上调用两个 Test() 调用，例如11，因为用 C++ 实现的典型 STA COM 对象就是这种情况。

一种可能的解决方案是禁用 .NET COM 对象上的 IMarshal 接口：

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
[ComDefaultInterface(typeof(IComObject))]
public class ComObject : IComObject, ICustomQueryInterface
{
    // IComObject methods
    public void Test()
    {
        Console.WriteLine(new { Environment.CurrentManagedThreadId });
    }

    public static readonly Guid IID_IMarshal = new Guid("00000003-0000-0000-C000-000000000046");

    public CustomQueryInterfaceResult GetInterface(ref Guid iid, out IntPtr ppv)
    {
        ppv = IntPtr.Zero;
        if (iid == IID_IMarshal)
        {
            return CustomQueryInterfaceResult.Failed;
        }
        return CustomQueryInterfaceResult.NotHandled;
    }
}

输出（根据需要）：

{ CurrentManagedThreadId = 11 }
{ 等于 = 假 }
{ CurrentManagedThreadId = 11 }

这可行，但感觉像是特定于实现的 hack。有没有更体面的方法来完成这项工作，比如我可能忽略的一些特殊互操作属性？请注意，在现实生活中，ComObject 由遗留的非托管应用程序使用（并被编组）。

Answer 1

您可以从 StandardOleMarshalObject or ServicedComponent 继承该效果：

Managed objects that are exposed to COM behave as if they had aggregated the free-threaded marshaler. In other words, they can be called from any COM apartment in a free-threaded manner. The only managed objects that do not exhibit this free-threaded behavior are those objects that derive from ServicedComponent or StandardOleMarshalObject.

Answer 2

为公开给 COM 的托管 class 可以派生自 StandardOleMarshalObject 提供了一个很好的解决方案。

虽然这让我开始思考，如何处理已经有基数 class 的情况，比如 System.Windows.Forms.Control，其继承中没有 StandardOleMarshalObject链?

事实证明，可以聚合标准 COM 封送拆收器。类似于自由线程封送拆收器的 CoCreateFreeThreadedMarshaler，有一个 API：CoGetStdMarshalEx。方法如下：

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
[ComDefaultInterface(typeof(IComObject))]
public class ComObject : IComObject, ICustomQueryInterface
{
    IntPtr _unkMarshal;

    public ComObject()
    {
        NativeMethods.CoGetStdMarshalEx(this, NativeMethods.SMEXF_SERVER, out _unkMarshal);
    }

    ~ComObject()
    {
        if (_unkMarshal != IntPtr.Zero)
        {
            Marshal.Release(_unkMarshal);
            _unkMarshal = IntPtr.Zero;
        }
    }

    // IComObject methods
    public void Test()
    {
        Console.WriteLine(new { Environment.CurrentManagedThreadId });
    }

    // ICustomQueryInterface
    public CustomQueryInterfaceResult GetInterface(ref Guid iid, out IntPtr ppv)
    {
        ppv = IntPtr.Zero;
        if (iid == NativeMethods.IID_IMarshal)
        {
            if (Marshal.QueryInterface(_unkMarshal, ref NativeMethods.IID_IMarshal, out ppv) != 0)
                return CustomQueryInterfaceResult.Failed;
            return CustomQueryInterfaceResult.Handled;
        }
        return CustomQueryInterfaceResult.NotHandled;
    }

    static class NativeMethods
    {
        public static Guid IID_IMarshal = new Guid("00000003-0000-0000-C000-000000000046");

        public const UInt32 SMEXF_SERVER = 1;

        [DllImport("ole32.dll", PreserveSig = false)]
        public static extern void CoGetStdMarshalEx(
            [MarshalAs(UnmanagedType.IUnknown)] object pUnkOuter,
            UInt32 smexflags,
            out IntPtr ppUnkInner);
    }
}

如何使 .NET COM 对象成为单元线程？

How to make make a .NET COM object apartment-threaded?

.net

c#

com

multithreading

com-interop