DispatchOperationRuntime.cs

class DispatchOperationRuntime
{
        //...
        void UninitializeCallContextCore(ref MessageRpc rpc)
        {
            IClientChannel channel = rpc.Channel.Proxy as IClientChannel;
            int offset = this.Parent.CallContextCorrelationOffset;
 
            try
            {
                for (int i = this.CallContextInitializers.Length - 1; i >= 0; i--)
                {
                    ICallContextInitializer initializer = this.CallContextInitializers[i];
                    initializer.AfterInvoke(rpc.Correlation[offset + i]);
                }
            }
            catch (Exception e)
            {
                // thread-local storage may be corrupt
                DiagnosticUtility.FailFast(string.Format(CultureInfo.InvariantCulture, "ICallContextInitializer.BeforeInvoke threw an exception of type {0}: {1}", e.GetType(), e.Message));
            }
        }
        //....
}

NhSessionPerCallContext.cs

public class NhSessionPerCallContext:ICallContextInitializer
{
        //...
        public void AfterInvoke(object correlationState)
        {
            var session = CurrentSessionContext.Unbind(_sessionFactory);
            if (session != null)
            {
                try
                {
                    session.Flush();
                    if (session.Transaction.IsActive)
                    {
                        session.Transaction.Commit();
                    }
                }
                catch (Exception e)
                {
                    if (session.Transaction.IsActive)
                    {
                        session.Transaction.Rollback();
                    }
                    throw;
                }
                finally
                {
                    session.Close();
                    session.Dispose();
                }
            }
        }
        //...
 }