Counting the number of messages in a Message Queue in .NET - unsafe version

MSMQCountUnsafe.cs

using System;
using System.Messaging;
using System.Runtime.InteropServices;

static class MessageQueueExtensions {
 
    [DllImport("mqrt.dll")]
    private unsafe static extern int MQMgmtGetInfo(char* computerName, char* objectName, MQMGMTPROPS* mgmtProps);
 
    private const byte VT_NULL = 1;
    private const byte VT_UI4 = 19;
    private const int PROPID_MGMT_QUEUE_MESSAGE_COUNT = 7;
 
    //size must be 16
    [StructLayout(LayoutKind.Sequential)]
    private struct MQPROPVariant {
        public byte vt;       //0
        public byte spacer;   //1
        public short spacer2; //2
        public int spacer3;   //4
        public uint ulVal;    //8
        public int spacer4;   //12
    }
 
    //size must be 16 in x86 and 28 in x64
    [StructLayout(LayoutKind.Sequential)]
    private unsafe struct MQMGMTPROPS {
        public uint cProp;
        public int* aPropID;
        public MQPROPVariant* aPropVar;
        public int* status;
    }   
    
    public static uint GetCount(this MessageQueue queue) {
        return GetCount(queue.Path);
    }
 
    private static unsafe uint GetCount(string path) {
        if (!MessageQueue.Exists(path)) {
            return 0;
        }
 
        MQMGMTPROPS props = new MQMGMTPROPS();
        props.cProp = 1;
 
        int aPropId = PROPID_MGMT_QUEUE_MESSAGE_COUNT;
        props.aPropID = &aPropId;
 
        MQPROPVariant aPropVar = new MQPROPVariant();
        aPropVar.vt = VT_NULL;
        props.aPropVar = &aPropVar;
 
        int status = 0;
        props.status = &status;
 
        IntPtr objectName = Marshal.StringToBSTR("queue=Direct=OS:" + path);
        try {
            int result = MQMgmtGetInfo(null, (char*)objectName, &props);
            if (result != 0 || *props.status != 0 || props.aPropVar->vt != VT_UI4) {
                return 0;
            } else {
                return props.aPropVar->ulVal;
            }
        } finally {
            Marshal.FreeBSTR(objectName);
        }
    }
}

public class MessageQueueExtensionsTest {

    public static void Main() {
     
        string queueName = @".\Private$\MyQueue";
     
        if (MessageQueue.Exists(queueName)) {
            MessageQueue.Delete(queueName);
        }
     
        MessageQueue queue = MessageQueue.Create(queueName);
        Console.WriteLine("Count should be 0: " + queue.GetCount());
     
        queue.Send("ping", "ping");
        Console.WriteLine("Count should be 1: " + queue.GetCount());
     
        queue.Send("ping2", "ping2");
        Console.WriteLine("Count should be 2: " + queue.GetCount());
     
        queue.Receive();
        Console.WriteLine("Count should be 1: " + queue.GetCount());
     
        queue.Send("ping3", "ping3");
        Console.WriteLine("Count should be 2: " + queue.GetCount());
     
        MessageQueue.Delete(queueName);
        Console.WriteLine("Count should be 0: " + queue.GetCount());
    }
}