jobjectpool

JObjectPool - Thread-Safe Object Pooling

Thread-safe, lock-free generic object pooling for Unity using CAS operations. Works with job system and async operations.

When to Use

• Frequently instantiated objects (bullets, enemies, effects)
• Reducing GC during gameplay
• Multi-threaded object reuse (safe from any thread)
• High-frequency object lifecycle operations

Core API

Constructor

new JObjectPool<T>(
    int maxSize = 64,           // Maximum pooled objects (excess discarded)
    Action<T> onRent = null,    // Called when renting (for initialization)
    Action<T> onReturn = null   // Called when returning (for cleanup)
)

Note: T must be a reference type with a parameterless constructor (where T : class, new()).

Methods

• .Rent() - Get object from pool or create new
• .Return(T obj) - Return object to pool (null values ignored)
• .Clear() - Remove all pooled objects
• .Prewarm(int count) - Pre-allocate objects (won't exceed maxSize)
• .Count - Current available count (approximate, thread-safe)

Static Access

• JObjectPool.Shared<T>() - Global shared pool per type (default config: maxSize=64)

Patterns

Basic Pool

var pool = new JObjectPool<Bullet>(maxSize: 100);
var bullet = pool.Rent();
// ... use bullet ...
pool.Return(bullet);

With Initialization on Rent

var pool = new JObjectPool<Enemy>(
    maxSize: 50,
    onRent: static enemy => enemy.Reset()
);

Reset State on Return (RECOMMENDED)

var pool = new JObjectPool<List<int>>(
    maxSize: 32,
    onReturn: static list => list.Clear()
);

Prewarm During Loading

var pool = new JObjectPool<Effect>();
pool.Prewarm(50);  // Pre-create during loading screen

Shared Pool (Simple Objects)

// Good for simple reusable objects without custom callbacks
var sb = JObjectPool.Shared<StringBuilder>().Rent();
sb.Append("Hello");
sb.Clear();  // Clean up before returning
JObjectPool.Shared<StringBuilder>().Return(sb);

Game Patterns (Zero-GC)

Bullet Pool with Struct Config

public sealed class Bullet
{
    public Vector3 Position;
    public Vector3 Velocity;
    public float Damage;
    public float Lifetime;

    public void Reset()
    {
        Position = default;
        Velocity = default;
        Damage = 0;
        Lifetime = 0;
    }
}

public sealed class BulletManager
{
    private readonly JObjectPool<Bullet> _pool = new(
        maxSize: 200,
        onReturn: static b => b.Reset());

    public void Initialize() => _pool.Prewarm(100);

    public Bullet Fire(in Vector3 pos, in Vector3 dir, float speed, float damage)
    {
        var bullet = _pool.Rent();
        bullet.Position = pos;
        bullet.Velocity = dir * speed;
        bullet.Damage = damage;
        return bullet;
    }

    public void Return(Bullet b) => _pool.Return(b);
}

Enemy Spawner (Zero-GC State)

public sealed class Enemy : IPoolable
{
    public float Health { get; set; }
    public Vector3 Position { get; set; }
    public event Action OnDeath;

    public void OnSpawn()
    {
        Health = 100f;
    }

    public void OnDespawn()
    {
        OnDeath = null;  // Clear delegates to prevent leaks
    }
}

public sealed class EnemySpawner
{
    private readonly JObjectPool<Enemy> _pool;

    public EnemySpawner(int maxSize = 50)
    {
        _pool = new(
            maxSize,
            onRent: static e => e.OnSpawn(),
            onReturn: static e => e.OnDespawn());
    }

    public Enemy Spawn(in Vector3 position)
    {
        var enemy = _pool.Rent();
        enemy.Position = position;
        return enemy;
    }

    public void Despawn(Enemy e) => _pool.Return(e);
}

Temporary Collection (Zero-GC in Update)

// Use in hot paths to avoid List<T> allocations
public void ProcessNearbyEnemies(in Vector3 center, float radius)
{
    var list = JObjectPool.Shared<List<Enemy>>().Rent();
    try
    {
        FindEnemiesNonAlloc(center, radius, list);
        foreach (var enemy in list)
        {
            ProcessEnemy(enemy);
        }
    }
    finally
    {
        list.Clear();
        JObjectPool.Shared<List<Enemy>>().Return(list);
    }
}

StringBuilder Pool (Zero-GC String Building)

public static string FormatDamage(float damage, string targetName)
{
    var sb = JObjectPool.Shared<StringBuilder>().Rent();
    try
    {
        sb.Append(targetName);
        sb.Append(" took ");
        sb.Append(damage.ToString("F1"));
        sb.Append(" damage");
        return sb.ToString();
    }
    finally
    {
        sb.Clear();
        JObjectPool.Shared<StringBuilder>().Return(sb);
    }
}

Best Practices

1. Pre-allocate during loading to prevent in-game allocation spikes
2. Reset state on return to prevent data leaks between reuses
3. Set appropriate maxSize based on expected concurrent usage
4. Use shared pools for simple objects without custom callbacks
5. Monitor pool Count to optimize sizing

Troubleshooting

Objects Not Reused

• Forgot to Return: Always call pool.Return(obj) when done
• Pool at capacity: Increase maxSize if concurrent usage exceeds limit
• Returning null: Null values are silently ignored

Stale Data / Memory Leaks

• Not resetting state: Clear all fields in onReturn callback
• Event delegates: Unsubscribe all events in onReturn to prevent leaks
• References to disposed objects: Null out references in onReturn

Performance Issues

• Not pre-warming: Call Prewarm() during loading screens
• maxSize too low: Causes allocations when pool empties
• maxSize too high: Wastes memory

Thread Safety

• JObjectPool IS thread-safe (lock-free CAS)
• Safe to Rent/Return from any thread
• onRent/onReturn run on calling thread

Common Mistakes

• Returning null to pool (ignored, but wasteful)
• Not clearing object state on return (causes bugs from stale data)
• Forgetting to return objects (pool becomes ineffective)
• Setting maxSize too low (causes frequent allocations)
• Setting maxSize too high (wastes memory)