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Design Pattern / Game Programming

[Game Programming] Event Queue Pattern

A pattern that lowers coupling between systems by separating event publishing and consuming through a queue.

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  • Design Pattern
  • Game Programming
Contents

One-line pattern summary

A pattern that lowers coupling between systems by separating event publishing and consuming through a queue.

Typical Unity use cases

  • When combat events need to be delivered to UI, audio, and rewards at the same time.
  • When you want to reduce tight coupling caused by immediate direct calls.

Parts (roles)

  • Publisher: event producer
  • Queue: event storage
  • Consumer: frame-based processor

Unity example (C#)

The code below is a simplified Unity example based on the scenario described above.

using System.Collections.Generic;
using UnityEngine;

public readonly struct CombatEvent
{
    public readonly string EventType;
    public readonly int Value;

    public CombatEvent(string eventType, int value)
    {
        EventType = eventType;
        Value = value;
    }
}

public sealed class CombatEventQueue : MonoBehaviour
{
    private readonly Queue<CombatEvent> pendingEvents = new();

    public void Publish(CombatEvent combatEvent)
    {
        pendingEvents.Enqueue(combatEvent);
    }

    private void Update()
    {
        while (pendingEvents.Count > 0)
        {
            CombatEvent combatEvent = pendingEvents.Dequeue();
            Debug.Log($"${combatEvent.EventType}: ${combatEvent.Value}");
        }
    }
}

Advantages

  • It separates producer and consumer timing, reducing direct dependencies between systems.
  • It makes extensions such as event logging, replay, and batch processing easier.

Things to watch out for

  • If the queue backs up, responsiveness can drop because of added latency.
  • If ordering and duplication rules are not defined clearly, hard-to-reproduce bugs can appear.

Interaction diagram

This shows the asynchronous flow where producers and consumers are separated by a queue.

flowchart LR

  queue["Event Queue"]

  subgraph producers["Producers"]
    combat["CombatSystem"]
    ai["AISystem"]
    loot["LootSystem"]
  end

  subgraph consumers["Consumers"]
    ui["UISystem"]
    audio["AudioSystem"]
    analytics["AnalyticsSystem"]
  end

  combat -->|enqueue| queue
  ai -->|enqueue| queue
  loot -->|enqueue| queue
  queue -->|dequeue| ui
  queue -->|dequeue| audio
  queue -->|dequeue| analytics

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