Lock Counter

using System;
using System.Threading;

class Program
{
    static readonly object Gate = new object();
    static int counter;
    static int rounds;

    static void Increment()
    {
        for (int step = 0; step < rounds; step++)
        {
            lock (Gate)
            {
                int next = counter + 1;
                counter = next;
            }
        }
    }

    static void Main()
    {
        int increments = 123;
        rounds = increments;
        counter = 0;

        Thread first = new Thread(Increment);
        Thread second = new Thread(Increment);

        first.Start();
        second.Start();

        first.Join();
        second.Join();

        Console.WriteLine($"increments={increments}");
        Console.WriteLine($"counter={counter}");
    }
}

using System;
using System.Threading;

class Program
{
    static readonly object Gate = new object();
    static int counter;
    static int rounds;

    static void Increment()
    {
        for (int step = 0; step < rounds; step++)
        {
            lock (Gate)
            {
                int next = counter + 1;
                counter = next;
            }
        }
    }

    static void Main()
    {
        int increments = 123;
        rounds = increments;
        counter = 0;

        Thread first = new Thread(Increment);
        Thread second = new Thread(Increment);

        first.Start();
        second.Start();

        first.Join();
        second.Join();

        Console.WriteLine($"increments={increments}");
        Console.WriteLine($"counter={counter}");
    }
}

using System;
using System.Threading;

class Program
{
    static readonly object Gate = new object();
    static int counter;
    static int rounds;

    static void Increment()
    {
        for (int step = 0; step < rounds; step++)
        {
            lock (Gate)
            {
                int next = counter + 1;
                counter = next;
            }
        }
    }

    static void Main()
    {
        int increments = 123;
        rounds = increments;
        counter = 0;

        Thread first = new Thread(Increment);
        Thread second = new Thread(Increment);

        first.Start();
        second.Start();

        first.Join();
        second.Join();

        Console.WriteLine($"increments={increments}");
        Console.WriteLine($"counter={counter}");
    }
}