Question

I know that I can’t modify a collection while iterating over it.

Normally I make a copy of the collection I want to iterate over, then iterate over the copy to avoid errors.

My program; however, makes lots of fast modifications to the collection I’m trying to make a copy of.

Could the error be occurring because I am making a copy while the parent collection is being modified?

I know ConcurrentDictionary provides some sort of locking mechanism for cross threading. Is there something similar I can use to prevent this error?

    // Original collection:
    Dictionary<string, Enemy> Dict_Enemies = new Dictionary<string, Enemy>();

    // Copy of original collection: (this line throws the exception)
    Dictionary<string, Enemy> Dict_Enemies_Copy = new Dictionary<string, Enemy>(Dict_Enemies);

Answer 1

Try using a ConcurrentDictionary for Dict_Enemies to allow it to be modified from multiple threads. Then make a copy of it in a thread-safe operation using the ToArray() method:

// Original collection:
var Dict_Enemies = new ConcurrentDictionary<string, Enemy>();

// Thread-safe copy:
ICollection<KeyValuePair<string, Enemy>> Dict_Enemies_Copy = Dict_Enemies.ToArray();