Using Locks using attribute in Async Await Scenario

AsyncLock.cs

 [Serializable]
    public class MethodLockedAttribute : MethodInterceptionAspect
    {
        private int maximum_concurrency_number;
        private static ConcurrentDictionary<int,SemaphoreSlim> SemaphoreSlimRepo=new ConcurrentDictionary<int, SemaphoreSlim>(); 
        public MethodLockedAttribute(int maximumConcurrencyNumber)
        {
            maximum_concurrency_number = maximumConcurrencyNumber;
        }

        public override async Task OnInvokeAsync(MethodInterceptionArgs args)
        {
            SemaphoreSlim semaphore=new SemaphoreSlim(maximum_concurrency_number);
            semaphore=SemaphoreSlimRepo.GetOrAdd(args.Method.GetMetadataToken(),  semaphore);
            await semaphore.WaitAsync();
            try
            {
            await args.ProceedAsync();
            }
            finally
            {
            semaphore.Release();
            }
        }
        
        
        
        
        
        [MethodLocked(3)]
        public async Task AddUser(string username)
        {
           await _users.AddAsync(username);
       }

        
    }