Question

After asking this question , I still have a question.

I got both excellent answers but I’m still having a trouble finding how could this actually be occur: ( how could a fault situation can occur) :

I will start with an example :

public void Do(string [] g)
{
   g=null;     //<========
}

void Main()
{
    var t=new string[3];
    t[0]="1";   t[1]="1";   t[2]="1";
    Do( t);
    Console.WriteLine ( t.Length);
}

the notated line can be execute in a different thread but each thread has its own g variable !
(and please remember that I can’t add items to an arrray. cause array length is created at creation)

No matter what will I do with the function Do – (no matter in what thread) , the Console.Writeline result will always be 3 ( unless using ref).

so lets see the real code :

    public static string Concat(params string[] values)
  #1  {
  #2      if (values == null)
  #3       {
  #4            throw new ArgumentNullException("values");
  #5       }
  #6        int totalLength = 0;
  #7        string[] strArray = new string[values.Length];
  #8        for (int i = 0; i < values.Length; i++)
  #9          {
  #10            string str = values[i];
  #11            strArray[i] = (str == null) ? Empty : str;
  #12            totalLength += strArray[i].Length;
  #13            if (totalLength < 0)
  #14            {
  #15                throw new OutOfMemoryException();
  #16            }
  #17         }
  #18        return ConcatArray(strArray, totalLength);
  #19   }

My saying is : once I’m on #1 , in thread X , this thread will forever will have array with length 3.

If another thread wants to destroy/change the array length ( which I cant understand how , cause the array has fixed length , all he can do is making it null) – it will have a different copy of pointer address.

I must be missing something here.

• What am I missing ?

• what is the code which other thread could execute which will cause an error ?(assuming we don’t copy the array).

Answer 1

what is the code which other thread could execute which will cause an error ?

string[] data = { "1", "2", "3" };
ThreadPool.QueueUserWorkItem( () => { data[0] = "one"; } );
string total = String.Concat(data);

Without the intermediate array there would be a race condition, the Thread could change data[0] after its length was added to totalLength but before the (presumably unsafe) call to ConcatArray(). The low-level method would then copy 5 chars to a buffer of size 3.