Function initialize_entity_index 

pub fn initialize_entity_index(plugin_index: &AtomicUsize) -> usize

Encapsulates the synchronization logic for initializing an entity’s index.

Acquires a global lock on the next available item index, but only increments it if we successfully initialize the provided index. The index of a registered item is assigned at runtime but only once per type. It’s possible for a single type to attempt to initialize its index multiple times from different threads, which is why all this synchronization is required. However, the overhead is negligible, as this initialization only happens once upon first access.

In fact, for our use case we know we are calling this function once for each type in each Entity’s ctor function, which should be the only time this method is ever called for the type.