Unable to add records to list passed as object to method

Question

I have this class :

Public class Error
{
     public string ErrorMessage { get; set; }
}

public class Test
    {
        public int Id { get; set; }
        public Import ImportResult { get; set; }
        public List<Error> Errors { get; set; }
        public void Start(object data)
        {
            object[] obj = data as object[];
            string[] importList = { "Item1", "Item2", "Item3", "Item4" };
            foreach (var item in importList)
            {
                object[] obj1 = new object[2];
                obj1[0] = item;
                obj1[1] = Errors;
                this.ImportResult = new Import(); 
                this.ImportResult.StartLongRunningProcess(obj1);//pass each import record to this method
            }
        }
    }

public class Import
    {
        public int Id { get; set; }
        public List<Error> Errors { get; set; }
        public void StartLongRunningProcess(object data) 
        {
            object[] datas = data as object[];
            string import = datas[0].ToString();
            try
            {
              // here I have along running process
            }
           // Here I store my error result in above list in long running process
            catch (Exception ex)
            {
               datas[1]. // Here I would like to add record to error list of Test class.
               Errors.Add(new Error
                 {
                    ErrorMessage =  ex.message
                 });
            }
        }
    }

Now what I am trying to do is I want to pass Error list of class Test as a parameter to StartLongRunningProcess method and from there I would like to store all error records in Error Variable of Test class.

The reason for doing this is because I have 1 method getCurrentData which is called every 5 second to get errors record currently running import item.So at the end of all import items I would have list of errors ready for all import item.

public string getCurrentData() //called every 5 seconds to get latest data
        {
           var data = TestList.FirstOrDefault(x => x.Key == 100).Value;
           response = new
           {
              errors = data.Errors.Select
                       (er => new
                       {
                            //error properties
                       }).ToList()   
           }

Parameter of StartLongRunningProcess is object because this method is running on threadpool from my another page that is why I have kept datatype as object for parameter data.

I also cannot make list of import like below :

  public List<Import> ImportResults = new List<Import>(); 

Answer 1

Question:

Start method of test class is running on thread pool.still Test.errors should be threadsafe??

Given your line:

this.ImportResult.StartLongRunningProcess(obj1);//pass each import record to this method

you just syncronously call method StartLongRunningProcess. In this particular case there's no need to worry about thread-safety because both Start and StartLongRunningProcess are executing in the same thread.

But then there's also no need to have StartLongRunningProcess with object parameter ;) Just let it take string importData, List<Error> errors.

But if StartLongRunningProcess is starting in another thread (than Start) and your start many of them in foreach loop then obviously you should be concerned about thread-safety. Because more than one StartLongRunningProcess running on different thread may call Errors.Add(error) of the same Test object.

...and now I just noticed your last note in the original question. Why you cannot do that? What compiler says?

---

First of all. There's no Errors initialization for both classes. Do it in constructor.

Second, change datas[1]. // Here i would like to add record to error list of Test class. to:

(data[1] as List<Error>).Add(new Error ...);

Does it work?

Btw, Test.Errors should be of thread-safe type against Add operation. For example, you can use ConcurrentQueue<T>.