Count local-thread allocations across arbitrary spans of code in Unity

AllocCounter.cs

using System;
using UnityEngine.Profiling;

// Borrowed directly from UnityEngine.TestTools.Constraints.AllocatingGCMemoryConstraint
public class AllocCounter {
    private Recorder _rec;

    public AllocCounter() {
        _rec = Recorder.Get("GC.Alloc");

        // The recorder was created enabled, which means it captured the creation of the
        // Recorder object itself, etc. Disabling it flushes its data, so that we can retrieve
        // the sample block count and have it correctly account for these initial allocations.
        _rec.enabled = false;

#if !UNITY_WEBGL
        _rec.FilterToCurrentThread();
#endif

        _rec.enabled = true;
    }

    public int Stop() {
        if (_rec == null) {
            throw new Exception("AllocCounter already stopped");
        }

        _rec.enabled = false;

#if !UNITY_WEBGL
        _rec.CollectFromAllThreads();
#endif

        var res = _rec.sampleBlockCount;
        _rec = null;
        return res;
    }

    public static int Instrument(Action action) {
        var counter = new AllocCounter();
        int allocs;
        try {
            action();
        } finally {
            allocs = counter.Stop();
        }

        return allocs;
    }
}

Usage example:

var ac = new AllocCounter();

// code that may or may not do allocations

var allocCount = ac.Stop();

Or use a lambda helper:

var allocCount = AllocCounter.Instrument(() => {
  // code that may or may not allocate
});

I wrote a little blog post that provides more context.