Using VC++ 6.0 COM DLL from Threads C# - c++

Question

BackGround:
We have DLL created using VC++6.0. This DLL in interface have functions that send message to our server. So external applications call function of our DLL by passing input parameter and our DLL send this message to a server using TCP/IP and return back a output for caller.
DLL is compiled with following settings
Main of DLL looks like this
I have created a samll application in C# (framework 2.0) that creates thread to call function of DLL. What happens is that second thread gets blocked until first thread has not finished the job.
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using PAGAMENTOLib;
using log4net;
using log4net.Config;
using System.Configuration;
namespace ThreadTestAPI
{
class Program
{
public static ILog log = LogManager.GetLogger(typeof(Program));
argpayClass apiFunctions = new argpayClass();
static void Main(string[] args)
{
XmlConfigurator.Configure();
List<string> Ip_List = new List<string>();
List<string> Ip_port = new List<string>();
int MAX_THREAD = Convert.ToInt32(ConfigurationManager.AppSettings["MAX_THREAD"].ToString());
string ReplacePattern = string.Empty;
string IP = ConfigurationManager.AppSettings["IP"].ToString();
string PORT = ConfigurationManager.AppSettings["PORT"].ToString();
Program call = new Program();
//int LastPart = Convert.ToInt32(IP.Split('*')[1]);
//string PatterntoReplase = "*" + LastPart;
log.Info("-------------------------------------------------------------------------");
log.Info(" Started Program ");
log.Info("-------------------------------------------------------------------------");
List<Thread> ThreadList = new List<Thread>(); //Added by Asif Iqbal
WaitAllThreads waitThreads = new WaitAllThreads();
List<Thread> myPOSthread = new List<Thread>();
ParamIn param = new ParamIn();
for (int i = 0; i < MAX_THREAD; i++)
{
Thread thread = new Thread(new ParameterizedThreadStart(call.CallApiFunction));
thread.Name = "Thread " + i;
param.Ped_ip = IP;
log.Info("Thread Name is : " + thread.Name);
log.Info("IP is " + param.Ped_ip);
param.PedPort = PORT.Replace("*",i.ToString());
log.Info("Port is " + param.PedPort);
param.Amount = i;
param.port_listener = "0";
param.DatiAgg = "Thread " + i;
ThreadList.Add(thread);
thread.IsBackground = true;
thread.TrySetApartmentState(ApartmentState.MTA);
thread.Start(param);
myPOSthread.Add(thread);
Console.WriteLine("***********************************************************");
Console.WriteLine("Thread Name: " + thread.Name);
System.Threading.Thread.Sleep(250);
}
}
[MTAThread]
public void CallApiFunction(object param)
{
log.Info("Calling Api function");
ParamIn members = (ParamIn)param;
//argpayClass apiFunctions = new argpayClass();
string Response = string.Empty;
apiFunctions.PagamentoTCP(0,500,ref members.Ped_ip,Convert.ToInt32(members.PedPort),ref members.DatiAgg,ref Response);
log.Info("IP is " + members.PedPort + ".Response Received from Api is: " + Response);
}
}
public class ParamIn
{
public int Amount;
public string DatiAgg;
public string PedPort;
public string Ped_ip;
public string ip_listener;
public string port_listener;
public int tmo;
public int PrintTicket;
public int Advance;
public ParamIn()
{
Amount = 0;
DatiAgg = "";
Ped_ip = "";
PedPort ="";
port_listener = "";
ip_listener = "";
tmo = 0;
PrintTicket = 0;
}
}
}
I tried to use
CoInitializeEx(NULL, COINIT_MULTITHREADED);
in DLL main but no success. I also changed this but still same behavior
public CComObjectRootEx<CComSingleThreadModel>
to public CComObjectRootEx<CComMultiThreadModel>
Does anyone know why Function of dll doesn't get called until first thread is in progress?
Whereas in c# threads were created correctly. Each thread finish job but not in pralall of others. It has to wait.

Answer 1

If you know your object’s implementation is thread safe and you want to tell .NET about that, implement IMarshal interface in your COM object.
Use CoCreateFreeThreadedMarshaler to create the marshaler, return the marshaler when .NET asks for IMarshal interface through QueryInterface call.
If you’re using ATL to implement your object, look at my answer for more info.