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⚡ optimize EventBus to prevent array allocations on Publish #185

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Merged
johnstrand merged 1 commit into from
Sep 12, 2026
Merged

⚡ optimize EventBus to prevent array allocations on Publish #185

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51 changes: 27 additions & 24 deletions src/GameUtils/Entity/EventBus.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,6 @@ namespace GameUtils.Entity;
public class EventBus
{
private readonly Dictionary<Type, object> _handlers = [];
private readonly Dictionary<Type, object> _snapshots = [];

/// <summary>
/// Subscribes <paramref name="handler"/> to events of type <typeparamref name="TEvent"/>.
Expand All @@ -17,19 +16,18 @@ public void Subscribe<TEvent>(Action<TEvent> handler)
ArgumentNullException.ThrowIfNull(handler);
var type = typeof(TEvent);

ref var listObj = ref System.Runtime.InteropServices.CollectionsMarshal.GetValueRefOrAddDefault(_handlers, type, out bool exists);
List<Action<TEvent>> list;
if (!exists)
ref var obj = ref System.Runtime.InteropServices.CollectionsMarshal.GetValueRefOrAddDefault(_handlers, type, out bool exists);
if (!exists || obj is not Action<TEvent>[] oldArray)
{
list = new List<Action<TEvent>>();
listObj = list;
obj = new Action<TEvent>[] { handler };
}
else
{
list = (List<Action<TEvent>>)listObj!;
var newArray = new Action<TEvent>[oldArray.Length + 1];
Array.Copy(oldArray, newArray, oldArray.Length);
newArray[oldArray.Length] = handler;
obj = newArray;
}
list.Add(handler);
_snapshots.Remove(type);
}

/// <summary>
Expand All @@ -41,12 +39,24 @@ public void Unsubscribe<TEvent>(Action<TEvent> handler)
ArgumentNullException.ThrowIfNull(handler);
var type = typeof(TEvent);

if (_handlers.TryGetValue(type, out var listObj))
if (_handlers.TryGetValue(type, out var obj) && obj is Action<TEvent>[] oldArray)
{
var list = (List<Action<TEvent>>)listObj;
if (list.Remove(handler))
int index = Array.IndexOf(oldArray, handler);
if (index < 0)
{
_snapshots.Remove(type);
return;
}

if (oldArray.Length == 1)
{
_handlers.Remove(type);
}
else
{
var newArray = new Action<TEvent>[oldArray.Length - 1];
Array.Copy(oldArray, 0, newArray, 0, index);
Array.Copy(oldArray, index + 1, newArray, index, oldArray.Length - index - 1);
_handlers[type] = newArray;
}
}
}
Expand All @@ -59,18 +69,13 @@ public void Unsubscribe<TEvent>(Action<TEvent> handler)
public void Publish<TEvent>(TEvent eventData)
{
var type = typeof(TEvent);
if (!_snapshots.TryGetValue(type, out var snapshot))
if (!_handlers.TryGetValue(type, out var obj))
{
if (!_handlers.TryGetValue(type, out var listObj))
{
return;
}
snapshot = ((List<Action<TEvent>>)listObj).ToArray();
_snapshots[type] = snapshot;
return;
}

var typedSnapshot = (Action<TEvent>[])snapshot;
foreach (var handler in typedSnapshot)
var handlers = (Action<TEvent>[])obj;
foreach (var handler in handlers)
{
handler(eventData);
}
Expand All @@ -82,7 +87,6 @@ public void Publish<TEvent>(TEvent eventData)
public void Clear()
{
_handlers.Clear();
_snapshots.Clear();
}

/// <summary>
Expand All @@ -92,6 +96,5 @@ public void Clear<TEvent>()
{
var type = typeof(TEvent);
_handlers.Remove(type);
_snapshots.Remove(type);
}
}
12 changes: 12 additions & 0 deletions tests/GameUtils.Benchmarks/EventBusBenchmarks.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,12 +12,18 @@ private class TestEvent2 { }

private Action<TestEvent1> _handler1 = null!;
private Action<TestEvent2> _handler2 = null!;
private EventBus _busWithSubscribers = null!;
private TestEvent1 _event1 = null!;

[GlobalSetup]
public void Setup()
{
_handler1 = e => { };
_handler2 = e => { };
_event1 = new TestEvent1();
_busWithSubscribers = new EventBus();
_busWithSubscribers.Subscribe(_handler1);
_busWithSubscribers.Subscribe(_handler2);
}

[Benchmark]
Expand All @@ -38,5 +44,11 @@ public void SubscribeExistingEvent()
bus.Subscribe(_handler1);
}
}

[Benchmark]
public void Publish()
{
_busWithSubscribers.Publish(_event1);
}
}
}
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