<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
    <system.serviceModel>
      <bindings>
        <wsHttpBinding>
          <binding name="SessionRel">
            <reliableSession enabled="true"/>
          <security mode="Message">
          </security>
          </binding>
        </wsHttpBinding>
      </bindings>
      <services>
        <service name="ServiceDefaultInstanceConcurrency.StockService">
           <host>
             <baseAddresses>
                <add baseAddress="http://localhost:8082/StockService"/>
             </baseAddresses>
           </host>
           <endpoint address="" bindingConfiguration="SessionRel" binding="wsHttpBinding" contract="ServiceDefaultInstanceConcurrency.IStockService"></endpoint>
          </service>
      </services>
    </system.serviceModel>
</configuration>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.ServiceModel;
using System.Threading;
using System.Runtime.Serialization;

namespace ServiceDefaultInstanceConcurrency
{
    [DataContract]
    public class StockPrice
    {
        [DataMember]
        public double price;
        [DataMember]
        public int calls;
    }
    [ServiceContract(SessionMode = SessionMode.Required)]
    public interface IStockService
    {
        [OperationContract]
        StockPrice GetPrice(string ticker);
    }
    [ServiceBehavior(InstanceContextMode = InstanceContextMode.PerSession, ConcurrencyMode = ConcurrencyMode.Multiple)]
    public class StockService : IStockService
    {
        object lockthis = new object();
        private int n_Calls = 0;
        StockService()
        {
            Console.WriteLine("{0} В потоке создан новый экземпляр StockService", DateTime.Now);

        }
        public StockPrice GetPrice(string ticker)
        {
            StockPrice p = new StockPrice();
            Console.WriteLine("{0}: GetPrice вызван в потоке {1}", DateTime.Now, Thread.CurrentThread.ManagedThreadId);
            Thread.Sleep(5000);
            p.price = 9.48;
            lock (lockthis)
            {
                p.calls = ++n_Calls;
            }
            return p;
        }
    }
   public class Program
    {

       public static void Main(string[] args)
        {
            ServiceHost host = new ServiceHost(typeof(StockService));
            host.Open();
            Console.WriteLine("Нажмите ENTER, чтобы завершить");
            Console.ReadLine();
            host.Close();
        }
    }
}