Key not found when calling world.Destroy about arch HOT 4 CLOSED

One thing that instantly comes into my mind is that you never should query and create/destroy entities at the same time.

Destroyed entities will be replaced with the last entity from the last used chunk, this is a mechanism used to always ensure dense packed arrays.

When we query entities and remove them at the same time, the query will not be notified about this. This may result in undefined behaviour, like that a lot of entities will not be queried since they were already moved to memory locations which the query already passed by. Or that the query probably runs too far since the underlaying chunks were modified. Its basically like you would do the following...

foreach(var myItem in myList){ 
   myList.Remove(myItem); // Throws exception since we iterate and remove at the same time, a big no go even for standard lists
 }

Future Solution

This behaviour will also NOT be altered, since such a notification mechanism would harm the query performance. However theres a feature planned called "CommandBuffer" which will allow you to record such entity modifications to push them to the world after the query finished.

Current Solution

Add entities you wanna remove to a list, iterate over the list AFTER the query to destroy the entities.

from arch.

Investigating :)

from arch.

         struct T { };
         struct K { };

          var arch = new Type[] { typeof(T), typeof(K) };

            for (int i = 0; i< 100; ++i)
                _world.Create(arch);

            var rng = new Random();
            while (true)
            {
                _world.Query(new QueryDescription() { All = arch }, (in Entity e, ref T t, ref K k) =>
                {
                    if (rng.Next() % 2 == 0)
                    {
                        _world.Destroy(in e);
                    }
                });
            }

At the exception throwing the _world.Size is > 0

A feature called CommandBuffer #17 is now in development and will make such behaviour possible :)

from arch.

Solved with #24 :) which adds multiple command buffers to record and playback structural changes.

         struct T { };
         struct K { };

          var arch = new Type[] { typeof(T), typeof(K) };
          var destructionBuffer = new DestructionBuffer(world);          

            for (int i = 0; i< 100; ++i)
                _world.Create(arch);

            var rng = new Random();
            while (true)
            {
                _world.Query(new QueryDescription() { All = arch }, (in Entity e, ref T t, ref K k) =>
                {
                    if (rng.Next() % 2 == 0)
                    {
                       destructionBuffer.Destroy(in e);
                    }
                });
                destructionBuffer.Playback();
            }

from arch.