Question

I have a small application that using BackgroundWorker to process the IEnumerator<T> list at all time.

The code basically like this:

while(true){
    foreach(T item in list){
       // Process each item and send process
       // Add an object in child List ( List<T1> item.Result )
    }
    Thread.Sleep(500);
}

Now I have a button and a textbox, which will add directly to the IEnumerator.

The problem is that after I add button, the backgroundworker continue to process it’s currently processing Item, but will stop after finish that item. It does not continue.

How can I safely add an Item to the list without affect the backgroundworker? Beside the background worker also do adding objects to the item. What should be the solution for this?

Thank you

Answer 1

Have the background worker iterate over a copy of the original list, not the list itself.

 while (true)
 {
       foreach (T item in new List<T>( list ))
       {
          ....
       }
       Thread.Sleep(500);
 }

If you attempt to modify a collection while enumerating over it, the enumerator will throw an exception. From the docs:

An enumerator remains valid as long as the collection remains
unchanged. If changes are made to the collection, such as adding,
modifying, or deleting elements, the enumerator is irrecoverably
invalidated and the next call to MoveNext or Reset throws an
InvalidOperationException. If the collection is modified between
MoveNext and Current, Current returns the element that it is set to,
even if the enumerator is already invalidated.