Benchmark Optimization

Introduction

C# Optimizations tips and tricks.

1. ReadOnlySpan() instead of Substring()

Instead of using .Substring() it is suggested of using .AsSpan() Click here for a detailed description and here and then hereand here.

Span<T> is a ref struct that is allocated on the stack rather than on the managed heap. 
Ref struct types have a number of restrictions to ensure that they cannot be promoted to the managed heap, 
including that they can't be boxed, they can't be assigned to variables of type Object, dynamic or to any interface type, 
they can't be fields in a reference type, and they can't be used across await and yield boundaries. In addition, calls to two methods, 
Equals(Object) and GetHashCode, throw a NotSupportedException.

Remarks:

No memory allocation. Looking at this code:

string s = "Hello world. This is a test!";
var a = s.AsSpan(0, 4);
var b = s.AsSpan(22);

In Visual Studio it is possible to show Memory allocation during Debug here:

By writing s it is possible to show the memory allocated for the string:

Insted by writing a or b we can see:

Benchmarks

We have used BenchmarkDotNet to test the performance of using AsSpan() comparing different ways of using a substring and a concat.

  [Benchmark]
  public void TestSubstring()
  {
      var res= string.Concat(test.Substring(0, 5), test.Substring(22));
  }

  [Benchmark]
  public void TestSpan()
  {
      var res = string.Concat(test.AsSpan(0, 4), test.AsSpan(22));
  }

  [Benchmark]
  public void TestSpanToString()
  {
      var res = test.AsSpan(0, 5).ToString() + test.AsSpan(22).ToString();
  }

  [Benchmark]
  public void TestSpanToStringConcat()
  {
      var res = string.Concat(test.AsSpan(0, 5).ToString(), test.AsSpan(22).ToString());
  }

As we can see the use of ReadOnlySpan has less memory allocation and then best performance.

Method	Mean	Error	StdDev	Gen0	Allocated
TestSpan	9.881 ns	0.1063 ns	0.1591 ns	0.0076	48 B
TestSubstring	26.882 ns	0.3570 ns	0.5343 ns	0.0191	120 B
TestSpanToString	27.900 ns	0.4150 ns	0.6083 ns	0.0191	120 B
TestSpanToStringConcat	28.036 ns	0.3850 ns	0.5762 ns	0.0191	120 B