gistfile1.txt

var dictionary = GetTheDictionary ();
IEnumerator e = dictionary.GetEnumerator ();
object current_dictionary_value;
while (true) {
    lock (dictionary) {
        try {
            if (!e.MoveNext ())
               break; // we're at the end of the dictionary
            current_dictionary_value = e.current;
        } catch {
            // An exception here means that the dictionary changed while we were iterating
            break;
        }
    }

    // Now we're outside of the lock, do our complex thing
    PerformTask (current_dictionary_value);
}


// When adding items to the dictionary, or modifying it in any way, lock it first and you sohuld be safe
lock (dictionary)
    dictionary.Add ("key", new object ());