Reduce allocation in Activity.{Parent}Id

[stephentoub]

When activities are enabled, we end up allocating Activity.Id eg once per HTTP request, and in addition to the result string, Id is allocating both a two-char string from a span as well as a string[6], both of which can be avoided.

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
Test	\main\corerun.exe	7.814 ms	1.00	22.89 MB	1.00
Test	\pr\corerun.exe	4.240 ms	0.54	12.97 MB	0.57

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Reflection;

[MemoryDiagnoser(false)]
[HideColumns("Error", "StdDev", "Median")]
public class Program
{
    public static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private Action<Activity, string> _setter;

    [GlobalSetup]
    public void Setup()
    {
        Activity.DefaultIdFormat = ActivityIdFormat.W3C;
        _setter = BuildSetter<Activity, string>(typeof(Activity).GetField("_id", BindingFlags.NonPublic | BindingFlags.Instance));
    }

    [Benchmark]
    public void Test()
    {
        using Activity activity = new Activity("Test");
        activity.Start();
        Action<Activity, string> setter = _setter;
        for (int i = 0; i < 100_000; i++)
        {
            _ = activity.Id;
            setter(activity, null);
        }
        activity.Stop();
    }

    private static Action<TSource, TArg> BuildSetter<TSource, TArg>(FieldInfo field)
    {
        ParameterExpression target = Expression.Parameter(typeof(TSource));
        ParameterExpression value = Expression.Parameter(typeof(TArg));
        return Expression.Lambda<Action<TSource, TArg>>(
            Expression.Assign(Expression.Field(target, field), value),
            target,
            value).Compile();
    }
}

[ghost]

Tagging subscribers to this area: @tarekgh, @tommcdon, @pjanotti
See info in area-owners.md if you want to be subscribed.

Issue Details

---

When activities are enabled, we end up allocating Activity.Id eg once per HTTP request, and in addition to the result string, Id is allocating both a two-char string from a span as well as a string[6], both of which can be avoided.

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
Test	\main\corerun.exe	7.814 ms	1.00	22.89 MB	1.00
Test	\pr\corerun.exe	4.240 ms	0.54	12.97 MB	0.57

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Reflection;

[MemoryDiagnoser(false)]
[HideColumns("Error", "StdDev", "Median")]
public class Program
{
    public static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private Action<Activity, string> _setter;

    [GlobalSetup]
    public void Setup()
    {
        Activity.DefaultIdFormat = ActivityIdFormat.W3C;
        _setter = BuildSetter<Activity, string>(typeof(Activity).GetField("_id", BindingFlags.NonPublic | BindingFlags.Instance));
    }

    [Benchmark]
    public void Test()
    {
        using Activity activity = new Activity("Test");
        activity.Start();
        Action<Activity, string> setter = _setter;
        for (int i = 0; i < 100_000; i++)
        {
            _ = activity.Id;
            setter(activity, null);
        }
        activity.Stop();
    }

    private static Action<TSource, TArg> BuildSetter<TSource, TArg>(FieldInfo field)
    {
        ParameterExpression target = Expression.Parameter(typeof(TSource));
        ParameterExpression value = Expression.Parameter(typeof(TArg));
        return Expression.Lambda<Action<TSource, TArg>>(
            Expression.Assign(Expression.Field(target, field), value),
            target,
            value).Compile();
    }
}

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.Diagnostics.Tracing
Milestone:	-