SemaphoreLocker.cs

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

namespace AdventOfCodePuzzles
{
    public class SemaphoreLocker
    {
        private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);

        public async Task LockAsync(Func<Task> worker)
        {
            await _semaphore.WaitAsync();
            try
            {
                await worker();
            }
            finally
            {
                _semaphore.Release();
            }
        }

        // overloading variant for non-void methods with return type (generic T)
        public async Task<T> LockAsync<T>(Func<Task<T>> worker)
        {
            await _semaphore.WaitAsync();
            try
            {
                return await worker();
            }
            finally
            {
                _semaphore.Release();
            }
        }
    }

}