using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    class Program
    {
        static SemaphoreSlim s = new SemaphoreSlim(1, 1);

        const int operations = 10000;
        static int balace = 0;

        static async Task Main(string[] args)
        {
            var tasks = new List<Task>();
            for (int index = 0; index < 10; index++)
            {
                balace = 0;
                for (int i = 0; i < operations; i++)
                {
                    tasks.Add(Task.Factory.StartNew(add));
                }
                for (int i = 0; i < operations; i++)
                {
                    tasks.Add(Task.Factory.StartNew(remove));
                }

                await Task.WhenAll(tasks);
                Console.WriteLine(balace);
            }
            Console.ReadLine();
        }

        static async Task add()
        {
            await s.WaitAsync();
            try
            {
                balace++;
                await Task.Yield();
            }
            finally
            {
                s.Release();
            }
        }
        static async Task remove()
        {
            await s.WaitAsync();
            try
            {
                balace--;
                await Task.Yield();
            }
            finally
            {
                s.Release();
            }
        }

    }
}

tasks.Add(await Task.Factory.StartNew(add));

tasks.Add(Task.Factory.StartNew(add).Unwrap());

tasks.Add(Task.Run(add));

G>>tasks.Add(await Task.Factory.StartNew(add));
G>>

G>>tasks.Add(Task.Factory.StartNew(add).Unwrap());
G>>

G>>tasks.Add(Task.Run(add));
G>>

Does not understand async delegates. This is actually the same as point 1 in the reasons why you would want to use StartNew. The problem is that when you pass an async delegate to StartNew, it’s natural to assume that the returned task represents that delegate. However, since StartNew does not understand async delegates, what that task actually represents is just the beginning of that delegate. This is one of the first pitfalls that coders encounter when using StartNew in async code.