Connection Pooling in multithreaded applications

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Common;
using ConnLibrary;

namespace ProjectBusiness
{
    public class Project
    {
        public List<Employee> Employees { get; set; }
        public string Name { get; set; }

        private object updateStatusLock = new object();

        /// <summary>
        /// Updates the status of Project
        /// </summary>
        /// <exception cref="System.Data.SqlClient.SqlException">System.Data.SqlClient.SqlException</exception>
        /// <exception cref="System.InvalidOperationException">System.InvalidOperationException</exception>
        public void UpdateStatus()
        {
            lock (updateStatusLock)
            {
                DBConnectionManager connManager = new DBConnectionManager();
                DbTransaction transaction = null;          
                try
                {
                    connManager.Connection.Open();
                    //It is Project objects responsibility to commit multiple Database updates in one transaction. 
                    transaction = connManager.Connection.BeginTransaction();
                    //some checks for project status..
                    string cmdString = "INSERT INTO PROJECTS VALUES('" + Name + "','Hello')";
                    connManager.Connection.ExecuteScalar(cmdString, transaction);
                    if (Employees != null)
                        foreach (Employee employee in Employees)
                            employee.UpdateStatus(this, transaction,connManager);
                    transaction.Commit();
                    transaction = null;
                }
                catch (System.InvalidOperationException invalidOperatioExcpetion)
                {
                    throw;
                }
                catch (System.Data.SqlClient.SqlException sqlException)
                {
                    throw;
                }
                catch
                {
                    throw;
                }
                finally
                {
                    if (connManager.Connection.IsOpen())
                    {
                       connManager.Connection.Close();
                    }
                    if (transaction != null)
                    {
                        transaction.Rollback();
                    }
                    transaction = null;
                    connManager = null;
                }
            }

        }


        /// <summary>
        /// Updates the status of Project
        /// </summary>
        /// <exception cref="System.Data.SqlClient.SqlException">System.Data.SqlClient.SqlException</exception>
        /// <exception cref="System.InvalidOperationException">System.InvalidOperationException</exception>
        public void UpdateStatusSingleton()
        {
            lock (updateStatusLock)
            {
                DbTransaction transaction = null;
                try
                {
                    SharedConnectionManager.Connection.Open();
                    //It is Project objects responsibility to commit multiple Database updates in one transaction. 
                    transaction = SharedConnectionManager.Connection.BeginTransaction();
                    //some checks for project status..
                    string cmdString = "INSERT INTO PROJECTS VALUES('" + Name + "','Hello')";
                    SharedConnectionManager.Connection.ExecuteScalar(cmdString, transaction);
                    if (Employees != null)
                        foreach (Employee employee in Employees)
                            employee.UpdateStatus(this, transaction);
                    transaction.Commit();
                    transaction = null;
                    SharedConnectionManager.Connection.Close();
                }
                catch (System.InvalidOperationException invalidOperatioExcpetion)
                {
                    throw;
                }
                catch (System.Data.SqlClient.SqlException sqlException)
                {
                    throw;
                }
                catch
                {
                    throw;
                }
                finally
                {
                    if (SharedConnectionManager.Connection.IsOpen())
                    {
                        SharedConnectionManager.Connection.Close();
                    }
                    if (transaction != null)
                    {
                        transaction.Rollback();
                    }
                    transaction = null;
                }
            }

        }
    }
}