ObservableInstrument.cs

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using System.Collections.Generic;
using System.Runtime.CompilerServices;
 
namespace System.Diagnostics.Metrics;
 
public abstract class ObservableInstrument<T> : Instrument where T : struct
{
    public override bool IsObservable => true;
 
    protected ObservableInstrument(Meter meter, string name, string? unit, string? description)
        : base(meter, name, unit, description)
    {
        Instrument.ValidateTypeParameter<T>();
    }
 
    protected abstract IEnumerable<Measurement<T>> Observe();
 
    internal override void Observe(MeterListener listener)
    {
        object subscriptionState = GetSubscriptionState(listener);
        IEnumerable<Measurement<T>> enumerable = Observe();
        if (enumerable == null)
        {
            return;
        }
        foreach (Measurement<T> item in enumerable)
        {
            listener.NotifyMeasurement(this, item.Value, item.Tags, subscriptionState);
        }
    }
 
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    internal IEnumerable<Measurement<T>> Observe(object callback)
    {
        if (callback is Func<T> func)
        {
            return new Measurement<T>[1]
            {
                new Measurement<T>(func())
            };
        }
        if (callback is Func<Measurement<T>> func2)
        {
            return new Measurement<T>[1] { func2() };
        }
        if (callback is Func<IEnumerable<Measurement<T>>> func3)
        {
            return func3();
        }
        return null;
    }
}