comtest.cs

using System;
using System.Runtime.InteropServices;

[Guid("00000002-0000-0000-C000-000000000046")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMalloc
{
    [PreserveSig]
    IntPtr Alloc(IntPtr cb);
    [PreserveSig]
    IntPtr Realloc(IntPtr pv, IntPtr cb);
    [PreserveSig]
    void Free(IntPtr pv);
    [PreserveSig]
    IntPtr GetSize(IntPtr pv);
    [PreserveSig]
    int DidAlloc(IntPtr pv);
    [PreserveSig]
    void HeapMinimize();
}

class Program
{
    [DllImport("ole32.dll")]
    static extern int CoGetMalloc(int context, out IMalloc ppMalloc);

    static void Main()
    {
        Marshal.ThrowExceptionForHR(CoGetMalloc(1, out IMalloc pMalloc));
        IntPtr p = pMalloc.Alloc(new IntPtr(4));
        p = pMalloc.Realloc(p, new IntPtr(100));
        pMalloc.DidAlloc(p);
        pMalloc.Free(p);
        pMalloc.HeapMinimize();
    }
}

test.cs

using System;
using System.Reflection;
using System.IO;
using System.Runtime.Loader;

class UnloadableAssemblyLoadContext : AssemblyLoadContext
{
    public UnloadableAssemblyLoadContext() : base(true)
    {
    }

    protected override Assembly Load(AssemblyName assemblyName)
    {
        return null;
    }
}

class My
{
    static void Work()
    {
        var alc = new UnloadableAssemblyLoadContext();
        alc.LoadFromAssemblyPath(Path.GetFullPath(@"comtest\comtest.exe")).EntryPoint.Invoke(null, null);
    }

    static void Main()
    {
        for (; ; )
        {
            Work();
        }
    }
}