C# Online Compiler | .NET Fiddle

using System;
using System.Linq;
using System.Threading.Tasks;

public class Program
{
	public static void Main()
	{
		var numbers = Enumerable.Range(0, 10);
		Parallel.ForEach(numbers, i =>
		{
			//Console.WriteLine("Task {0}:", i);
			var vm = VoteMachine.Instance;
			vm.RegisterVote();
		});
		Console.WriteLine("Total Votes: {0}", VoteMachine.Instance.TotalVote);
	}
}

public class VoteMachine
{
	private static VoteMachine _instance = null;
	private int _totalVote = 0;
	private static readonly object padlock = new object ();
	
	private VoteMachine()
	{
	}

	public static VoteMachine Instance
	{
		get
		{
			lock (padlock)
			{
				if (_instance == null)
				{
					_instance = new VoteMachine();
				}
			}

			return _instance;
		}
	}

	public void RegisterVote()
	{
		_totalVote += 1;
		Console.WriteLine("Registered Vote #" + _totalVote);
	}

	public int TotalVote
	{
		get
		{
			return _totalVote;
		}
	}
}

 
using System;
using System.Linq;
using System.Threading.Tasks;
​
public class Program
{
    public static void Main()
    {
        var numbers = Enumerable.Range(0, 10);
        Parallel.ForEach(numbers, i =>
        {
            //Console.WriteLine("Task {0}:", i);
            var vm = VoteMachine.Instance;
            vm.RegisterVote();
        });
        Console.WriteLine("Total Votes: {0}", VoteMachine.Instance.TotalVote);
    }
}
​
public class VoteMachine
{
    private static VoteMachine _instance = null;
    private int _totalVote = 0;
    private static readonly object padlock = new object ();