Span and Benchmarking in Csharp

Span instead of String in Csharp

By using Span (in combination with fitting methods like Slice()) we can remove expensive Allocation on the heap alltogether.

namespace span;

class Program
{
    private static readonly string _dateAsText = "20.07.2022";
    static void Main(string[] args)
    {
        Console.WriteLine(DateFromString());
        Console.WriteLine(DateFromSpan());
    }

    public static (int day, int month, int year) DateFromString(){
        var dayTxt = _dateAsText.Substring(0,2);    // here we allocate "20",
        var monthTxt = _dateAsText.Substring(3,2);  // here "07",
        var yearTxt = _dateAsText.Substring(6);     // and here "2022" on the heap.
        var day = int.Parse(dayTxt);
        var month = int.Parse(monthTxt);
        var year = int.Parse(yearTxt);
        return (day, month, year);                  // they get cleaned when leaving scope.
    }

    public static (int day, int month, int year) DateFromSpan(){
        ReadOnlySpan<char> dateAsSpan = _dateAsText;
        var dayTxt = dateAsSpan.Slice(0,2);
        var monthTxt = dateAsSpan.Slice(3,2);
        var yearTxt = dateAsSpan.Slice(6);
        var day = int.Parse(dayTxt);
        var month = int.Parse(monthTxt);
        var year = int.Parse(yearTxt);
        return (day, month, year);
    }
}

• Span will only need to store a pointer and some data about the length of the slice. this can all stay on the Stack. So it will always outperform heap allocations by a ton.

Benchmarking Class in Csharp

1. Add the BenchmarkDotNet Nu Get package. dotnet add package BenchmarkDotNet
2. create a class having one more more methods decorated with the Benchmark attribute.
3. Run your benchmark project in Release mode using the Run method of the BenchmarkRunner

Example of Benchmarking the above code:

• run it with: dotnet run -c Release

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
namespace span;

class Program
{
    static void Main(string[] args)
    {
        BenchmarkRunner.Run<BenchmarkDemo>();
    }
}

[MemoryDiagnoser]
public class BenchmarkDemo{
    private static readonly string _dateAsText = "20.07.2022";
    
    [Benchmark]
    public (int day, int month, int year) DateFromString(){
        var dayTxt = _dateAsText.Substring(0,2);
        var monthTxt = _dateAsText.Substring(3,2);
        var yearTxt = _dateAsText.Substring(6);
        var day = int.Parse(dayTxt);
        var month = int.Parse(monthTxt);
        var year = int.Parse(yearTxt);
        return (day, month, year);
    }

    [Benchmark]
    public (int day, int month, int year) DateFromSpan(){
        ReadOnlySpan<char> dateAsSpan = _dateAsText;
        var dayTxt = dateAsSpan.Slice(0,2);
        var monthTxt = dateAsSpan.Slice(3,2);
        var yearTxt = dateAsSpan.Slice(6);
        var day = int.Parse(dayTxt);
        var month = int.Parse(monthTxt);
        var year = int.Parse(yearTxt);
        return (day, month, year);
    }
}

Results:

|         Method |     Mean |    Error |   StdDev |   Gen0 | Allocated |
|--------------- |---------:|---------:|---------:|-------:|----------:|
| DateFromString | 48.34 ns | 0.070 ns | 0.062 ns | 0.0459 |      96 B |
|   DateFromSpan | 34.75 ns | 0.254 ns | 0.238 ns |      - |         - |