Implementing Debounce Method

[kenofori]

Hi there,

Could you please advise on how to implement a debounce method without any allocations?
https://angular.io/guide/http-optimize-server-interaction

I'm using it for an autocomplete feature, so I need only the last event after a specified delay to trigger the listener. I tried using UniTask but wasn't successful, and unfortunately, I haven't received any responses there, and even AI-generated code didn't work correctly.
Cysharp/UniTask#583

Thanks

[timcassell]

Assuming you are using Unity, you could implement your own IAwaitInstruction.

public class Debouncer : IAwaitInstruction
{
    private float _remainingSeconds;

    public Debouncer(float seconds)
        => Reset(_remainingSeconds);

    public void Reset(float seconds)
        => _remainingSeconds = seconds;

    bool IAwaitInstruction.IsCompleted()
        => (_remainingSeconds -= Time.unscaledDeltaTime) <= 0;
}

You can reset it for each keystroke, and pool it if you want to avoid allocations.

_debouncer = new Debouncer(0.5f);
await _debouncer;

_debouncer.Reset(0.5f);

[timcassell]

Or you could use a system timer. https://learn.microsoft.com/en-us/dotnet/api/system.timers.timer

[kenofori]

Thank you very much @timcassell , I tried with System Timer but it depends on https://github.com/PimDeWitte/UnityMainThreadDispatcher because i listen the event in a MonoBehaviour and further dispatch it.

Performance wise, in unity which would you recommend? Timer+MainThreadDispatcher Or IAwaitInstruction?

[timcassell]

I would just use IAwaitInstruction in Unity, especially since system timers are not supported in WebGL.

[kenofori]

Thanks, im confused when to await?
do i add flag that first check if its running (on first keystroke) and then start awaiting it? and if its already running it then i simply deduct the time as you are doing?

from api point of view, i simply want to call debounce whenever user hits a keystroke, and when i create intput field for the first time there wont be any awaiting happening, it will only happen when user first start typing

here is rough code

`

    private float _remainingSeconds;
    private bool isRunning;

    bool IAwaitInstruction.IsCompleted()
    {

        _remainingSeconds -= Time.unscaledDeltaTime;

        if (_remainingSeconds <= 0)
        {
            onDefaultEvent(this);

            isRunning = false;
            
            return false;
        }
        
        return true;
        
    }
    
    public override void SetDebounceTimeInSeconds(float debounceTimeInSeconds)
    {
        base.SetDebounceTimeInSeconds(debounceTimeInSeconds);
        _remainingSeconds = debounceTimeInSeconds;
    }



    public override void DebounceMethod()
    {
        _remainingSeconds = delayInSeconds;
        
        if (isRunning == false)
        {
            isRunning = true;
            await this; // confused here

        }
    }
    `

[timcassell]

- public override void DebounceMethod()
+ public override async void DebounceMethod()

[Edit]

To avoid allocations, you can do it like this:

public override void DebounceMethod()
{
    _remainingSeconds = delayInSeconds;
    
    if (isRunning == false)
    {
        isRunning = true;
        this.ToPromise().Forget();
    }
}