railroader-setons-special-sauce/mcp-tools/SparseHitchSampler.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using S3.Modules.Profiler;
using UnityEngine;

namespace S3.Mcp.Tools;

/// <summary>
/// Low-allocation manual sampler. It stores full probe detail only for hitch
/// frames and ignores sub-0.1ms samples, avoiding profiler-induced GC stalls.
/// </summary>
internal static class SparseHitchSampler
{
    static readonly Dictionary<string, HitchProbeSample> Current =
        new(StringComparer.Ordinal);
    static readonly List<HitchFrameRecord> Frames = new(4096);
    static GameObject? _driverObject;
    static float _threshold;
    static int _frame;
    static int _gc0;
    static int _gc1;
    static int _gc2;
    static long _mono;
    static bool _pending;

    public static bool Active { get; private set; }

    public static void Begin(float thresholdMs)
    {
        Cancel();
        Current.Clear();
        Frames.Clear();
        _threshold = thresholdMs;
        _frame = 0;
        _gc0 = GC.CollectionCount(0);
        _gc1 = GC.CollectionCount(1);
        _gc2 = GC.CollectionCount(2);
        _mono = UnityEngine.Profiling.Profiler.GetMonoUsedSizeLong();
        _pending = false;
        Active = true;
        _driverObject = new GameObject("S3 Sparse Hitch Sampler");
        _driverObject.hideFlags = HideFlags.HideAndDontSave;
        UnityEngine.Object.DontDestroyOnLoad(_driverObject);
        _driverObject.AddComponent<SparseHitchFrameDriver>();
    }

    public static List<HitchFrameRecord> End()
    {
        Active = false;
        DestroyDriver();
        Current.Clear();
        _pending = false;
        return new List<HitchFrameRecord>(Frames);
    }

    public static void Cancel()
    {
        Active = false;
        DestroyDriver();
        Current.Clear();
        Frames.Clear();
        _pending = false;
    }

    public static void Record(string id, long ticks, int calls = 1)
    {
        if (!Active || ticks <= Stopwatch.Frequency / 10_000) return;
        if (!Current.TryGetValue(id, out HitchProbeSample? sample))
        {
            sample = new HitchProbeSample();
            Current[id] = sample;
        }
        sample.Calls += calls;
        sample.Ticks += ticks;
        if (ticks > sample.MaxTicks) sample.MaxTicks = ticks;
    }

    public static void Advance(float frameMs)
    {
        if (!Active) return;
        int gc0 = GC.CollectionCount(0);
        int gc1 = GC.CollectionCount(1);
        int gc2 = GC.CollectionCount(2);
        long mono = UnityEngine.Profiling.Profiler.GetMonoUsedSizeLong();

        if (_pending && frameMs > 0f && frameMs < 2000f)
        {
            var frame = new HitchFrameRecord
            {
                Phase = "manual-sparse",
                Frame = _frame++,
                FrameMs = frameMs,
                Gc0 = gc0 - _gc0,
                Gc1 = gc1 - _gc1,
                Gc2 = gc2 - _gc2,
                MonoDelta = mono - _mono,
                CameraPosition = Camera.main != null
                    ? Camera.main.transform.position
                    : Vector3.zero,
            };
            if (frameMs >= _threshold)
            {
                foreach (var pair in Current)
                {
                    HitchProbeSample sample = pair.Value;
                    if (sample.Calls == 0) continue;
                    frame.Probes[pair.Key] = new HitchProbeSample
                    {
                        Calls = sample.Calls,
                        Ticks = sample.Ticks,
                        MaxTicks = sample.MaxTicks,
                    };
                }
            }
            Frames.Add(frame);
        }

        foreach (HitchProbeSample sample in Current.Values)
        {
            sample.Calls = 0;
            sample.Ticks = 0;
            sample.MaxTicks = 0;
        }
        _gc0 = gc0;
        _gc1 = gc1;
        _gc2 = gc2;
        _mono = mono;
        _pending = true;
    }

    static void DestroyDriver()
    {
        if (_driverObject == null) return;
        UnityEngine.Object.Destroy(_driverObject);
        _driverObject = null;
    }
}

[DefaultExecutionOrder(-31999)]
public sealed class SparseHitchFrameDriver : MonoBehaviour
{
    void Update() =>
        SparseHitchSampler.Advance(Time.unscaledDeltaTime * 1000f);
}