objectPool.cs

public class PoolItem<T> : IDisposable
  {
      private readonly Action<PoolItem<T>> _onRelease;
      public T Value { get; }

      public PoolItem(T value, Action<PoolItem<T>> onRelease)
      {
          _onRelease = onRelease;
          Value = value;
      }

      public void Dispose()
      {
          _onRelease(this);
      }
  }


  public class ObjectPool<T>
  {
      private readonly object _root = new();
      private readonly Func<T> _fabric;
      private readonly ConcurrentQueue<T> _pool = new();

      public ObjectPool(Func<T> fabric)
      {
          _fabric = fabric;
      }

      public PoolItem<T> Take()
      {
          var item = _pool.TryDequeue(out var x) ? x : _fabric();

          return new PoolItem<T>(item, Release);
      }

      public void Release(PoolItem<T> item)
      {
          _pool.Enqueue(item.Value);
      }
  }

  public static class Test 
  {
      public static async Task Run()
      {
          var httpPool = new ObjectPool<HttpClient>(() => new HttpClient());

          using (var http = httpPool.Take())
          {
              await http.Value.GetAsync("asdasd");
          }

          Console.WriteLine("обьект вернулся в пул");
      }
  }