generate random keys.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Jobs;
using System.Buffers;
using System.Text;

public class Program
{
    public static async Task Main(string[] args)
    {
#if DEBUG
        await new VariableLengthReaderBenchmark().Generate();
#else
        var summary = BenchmarkRunner.Run(typeof(Program).Assembly);
#endif

    }
}

// ``` ini
// 
// BenchmarkDotNet=v0.13.1, OS=Windows 10.0.18363.1440 (1909/November2019Update/19H2)
// Intel Core i7-8650U CPU 1.90GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
// .NET SDK=6.0.100
//   [Host]   : .NET 6.0.0 (6.0.21.52210), X64 RyuJIT
//   .NET 6.0 : .NET 6.0.0 (6.0.21.52210), X64 RyuJIT
// 
// Job=.NET 6.0  Runtime=.NET 6.0  
// 
// ```
// |          Method |    Count | KeySize |       Mean |    Error |   StdDev |     Gen 0 |     Gen 1 |     Gen 2 |  Allocated |
// |---------------- |--------- |-------- |-----------:|---------:|---------:|----------:|----------:|----------:|-----------:|
// |        Generate |  1000000 |       7 |   241.3 ms |  3.75 ms |  3.68 ms |         - |         - |         - |     250 KB |
// | Generate_unique |  1000000 |       7 |   408.0 ms |  8.00 ms | 12.22 ms | 1000.0000 | 1000.0000 | 1000.0000 |  18,426 KB |
// |        Generate | 10000000 |       7 | 2,450.7 ms | 27.99 ms | 26.18 ms |         - |         - |         - |   1,004 KB |
// | Generate_unique | 10000000 |       7 | 4,609.6 ms | 42.15 ms | 39.43 ms | 1000.0000 | 1000.0000 | 1000.0000 | 157,255 KB |


[MemoryDiagnoser]
[SimpleJob(RuntimeMoniker.Net60)]
public class VariableLengthReaderBenchmark
{
    [Params(1_000_000, 10_000_000)]
    public int Count { get; set; }

    [Params(7)]
    public int KeySize { get; set; }

    [Benchmark]
    public async Task Generate()
    {
        var fullFileName = GetFileName();
        await using var streamWriter = new StreamWriter(path: fullFileName, append: false, Encoding.UTF8, bufferSize: (int)Math.Pow(2, 15));

        var i = 0;
        foreach (var key in GenerateKeys(KeySize))
        {
            if (i++ == Count)
                break;

            await streamWriter.WriteLineAsync(key);
        }
    }

    [Benchmark]
    public async Task Generate_unique()
    {
        var fullFileName = GetFileName();
        await using var streamWriter = new StreamWriter(path: fullFileName, append: false, Encoding.UTF8, bufferSize: (int)Math.Pow(2, 15));

        var i = 0;
        var uniques = new HashSet<int>(Count);
        foreach (var key in GenerateKeys(KeySize))
        {
            if (uniques.Add(string.GetHashCode(key.Span)) is false)
                continue;

            if (i++ == Count)
                break;

            await streamWriter.WriteLineAsync(key);
        }
    }

    string GetFileName() => Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "keys.txt");

    IEnumerable<ReadOnlyMemory<char>> GenerateKeys(int keySize)
    {
        const int min = 'A';
        const int max = 'Z';

        var buffer = ArrayPool<char>.Shared.Rent(keySize);
        var memory = buffer.AsMemory().Slice(0, keySize);

        var random = new Random();
        var hashSet = new HashSet<char>(keySize);

        try
        {
            for (int line = 0, written = 0; ; line++, written = 0)
            {
                while (written < keySize)
                {
                    var c = (char)random.Next(min, max);

                    if (hashSet.Add(c))
                    {
                        buffer[written++] = c;
                    }
                }

                yield return memory;

                hashSet.Clear();
            }
        }
        finally
        {
            ArrayPool<char>.Shared.Return(buffer);
        }
    }
}