# GetOrCreateSystemsAndLogException(NativeList<SystemTypeIndex>, AllocatorHandle)

> Creates systems from the list of types which aren't already created in the current world.

## Definition

* **Type:** Method
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

```csharp
public NativeList<SystemHandle> GetOrCreateSystemsAndLogException(NativeList<SystemTypeIndex> types, AllocatorManager.AllocatorHandle allocator)
```

### Parameters

**** (\[NativeList\<SystemTypeIndex>]\(/engine/7000.0/script-reference/unity/collections/nativelist1)): The system types to create, in the order in which they should be created.**** (\[AllocatorHandle]\(/engine/7000.0/script-reference/unity/collections/allocatormanager/allocatorhandle)): The allocator to use to allocate the output system list

### Returns

| Type                                                                                          | Description                |
| --------------------------------------------------------------------------------------------- | -------------------------- |
| [NativeList\<SystemHandle>](/engine/7000.0/script-reference/unity/collections/nativelist1.md) | A list of system instances |

### Remarks

This function creates systems in the order they are passed in, and ignores [CreateBeforeAttribute](/engine/7000.0/script-reference/unity/entities/createbeforeattribute.md) and [CreateAfterAttribute](/engine/7000.0/script-reference/unity/entities/createafterattribute.md) validity. If errors are encountered either when creating the system or when calling OnCreate, a default [SystemHandle](/engine/7000.0/script-reference/unity/entities/systemhandle.md) will be returned for that system.

**Important:** This function creates a sync point if any systems are created, which means that the EntityManager waits for all currently running Jobs to complete before creating the systems, and no additional Jobs can start before the function is finished. A sync point can cause a drop in performance because the ECS framework may not be able to make use of the processing power of all available cores.