Preventing a class method from executing more than once at a time

Question

I have a asp.net mvc controller that when executed calls a method in a service class to open a file and start the import of records into a database. I'd somehow like to restrict this method or class so that another instance can't be created and prevent the method from being invoked again until it is done running. I've read about the singleton pattern but I'm not sure if it can be implemented because the class is instantiated by dependency injection.

Dependency injection is handled by Autofac

Service Class:

namespace Nop.Plugin.Misc.CAImport.Services
{    
    public class CAImportService: ICAImportService
    {
        #region Fields
        private IProductService _productService;
        private ICategoryService _categoryService;
        private IManufacturerService _manufacturerService;

        #endregion

        #region Constructor
        public CAImportService(IProductService productService, 
            ICategoryService categoryService,
            IManufacturerService manufacturerService)
        {
            this._productService = productService;
            this._categoryService = categoryService;
            this._manufacturerService = manufacturerService;
        }
        #endregion

        #region Methods
        /// <summary>
        /// Import products from tab delimited file
        /// </summary>
        /// <param name="fileName">String</param>
        public virtual void ImportProducts(string fileName, bool deleteProducts)
        {
            //Do stuff to import products

        }

        #endregion
    }
}

Controller Class:

namespace Nop.Plugin.Misc.CAImport.Controllers
{
    public class MiscCAImportController: BasePluginController
    {
        private ICAImportService _caImportService;

        public MiscCAImportController(ICAImportService caImportService)
        {
            this._caImportService = caImportService;
        }

        [AdminAuthorize]
        public ActionResult ImportProducts()
        {
            return View("~/plugins/misc.caimport/views/misccaimport/ImportProducts.cshtml");
        }

        [HttpPost]
        [AdminAuthorize]
        public ActionResult ImportProducts(ImportProductsModel model)
        {
            string fileName = Server.MapPath(model.Location);

            _caImportService.ImportProducts(fileName, model.DeleteProducts);                    

            return View("~/plugins/misc.caimport/views/misccaimport/ImportProducts.cshtml", model);
        }
    }
}

Answer 1

The code below adds a lock into your service to keep other threads from executing the enclosed statements concurrently.

public class CAImportService: ICAImportService
{

    // OTHER METHODS AND SECTIONS REMOVED FOR CLARITY

    // Define static object for the lock
    public static readonly object _lock = new object();

    /// <summary>
    /// Import products from tab delimited file
    /// </summary>
    /// <param name="fileName">String</param>
    public virtual void ImportProducts(string fileName, bool deleteProducts)
    {
        lock (_lock)
        {
            //Do stuff to import products
        }
    }
}