added benchmarks

ParadoxSaveParser.Benchmarks/JqBenchmarks.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Diagnostics;
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Engines;
+
+namespace ParadoxSaveParser.Benchmarks;
+
+/// <summary>
+///     jq runs as an external process on the JSON twin of the save.
+///     Numbers therefore include process start and reading the file from the OS page cache,
+///     which is exactly what you pay when you shell out to jq.
+///     <see cref="JqNoop" /> measures that fixed overhead so it can be subtracted.
+/// </summary>
+[SimpleJob(RunStrategy.Monitoring, launchCount: 1, warmupCount: 1, iterationCount: 5)]
+public class JqBenchmarks
+{
+    public static string JqPath { get; set; } = "jq";
+
+    [GlobalSetup]
+    public void Setup() => Run("--version", null);
+
+    [Benchmark(Description = "jq  .countries | map_values(.technology)")]
+    public int Jq() => Run("-c", BenchData.JqQuery);
+
+    [Benchmark(Description = "jq  empty (parse only)")]
+    public int JqParseOnly() => Run("-c", "empty");
+
+    [Benchmark(Description = "jq  --stream (no DOM)")]
+    public int JqStream() => Run("-c --stream", "empty");
+
+    [Benchmark(Description = "jq  process startup only (tiny input)")]
+    public int JqNoop()
+    {
+        var psi = new ProcessStartInfo(JqPath)
+        {
+            RedirectStandardOutput = true,
+            RedirectStandardInput = true,
+            UseShellExecute = false,
+        };
+        psi.ArgumentList.Add("-c");
+        psi.ArgumentList.Add("empty");
+        using var p = Process.Start(psi)!;
+        p.StandardInput.Write("{}");
+        p.StandardInput.Close();
+        p.StandardOutput.ReadToEnd();
+        p.WaitForExit();
+        return p.ExitCode;
+    }
+
+    private static int Run(string flags, string? program)
+    {
+        var psi = new ProcessStartInfo(JqPath)
+        {
+            RedirectStandardOutput = true,
+            RedirectStandardError = true,
+            UseShellExecute = false,
+        };
+        foreach (var f in flags.Split(' ', StringSplitOptions.RemoveEmptyEntries))
+            psi.ArgumentList.Add(f);
+        if (program != null)
+        {
+            psi.ArgumentList.Add(program);
+            psi.ArgumentList.Add(BenchData.JsonPath);
+        }
+
+        using var p = Process.Start(psi)!;
+        // output must be drained, otherwise jq blocks on a full pipe
+        long bytes = 0;
+        var buf = new char[1 << 16];
+        int read;
+        while ((read = p.StandardOutput.Read(buf, 0, buf.Length)) > 0)
+            bytes += read;
+        p.StandardError.ReadToEnd();
+        p.WaitForExit();
+        if (p.ExitCode != 0)
+            throw new Exception($"jq exited with {p.ExitCode}");
+        return (int)(bytes & int.MaxValue);
+    }
+}