Invalidation Listener needed #3
Description
When an iterator is created, the underlying data structure cannot be modified outside of the iterator. In order to handle potential hard to debug problems this could cause in a multi-threaded context, it is necessary to inform each structure when it has an iterator utilizing it. If the structure knows it has an iterator active, and then it receives a function call to edit itself, it should then throw an assertion error.
This would also imply that each of the iterator constructors would need to seize the writing mutex.