TimedDestroySystem.cs

using Unity.Entities;
using Unity.Jobs;

namespace ECS.Systems
{
	[UpdateAfter(typeof(MoveForwardSystem))]
	public class TimedDestroySystem : JobComponentSystem
	{
		EndSimulationEntityCommandBufferSystem buffer;

		protected override void OnCreate()
		{
			buffer = World.DefaultGameObjectInjectionWorld.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
		}

		struct CullingJob : IJobForEachWithEntity<TimeToLive>
		{
			public EntityCommandBuffer.Concurrent commands;
			public float dt;

			public void Execute(Entity entity, int jobIndex, ref TimeToLive timeToLive)
			{
				timeToLive.Value -= dt;
				if (timeToLive.Value <= 0f)
					commands.DestroyEntity(jobIndex, entity);
			}
		}

		protected override JobHandle OnUpdate(JobHandle inputDeps)
		{
			var job = new CullingJob
			{
				commands = buffer.CreateCommandBuffer().ToConcurrent(),
				dt = UnityEngine.Time.deltaTime
			};

			var handle = job.Schedule(this, inputDeps);
			buffer.AddJobHandleForProducer(handle);

			return handle;
		}
	}
}