From 3d7d2f543e792fd79f2c5cd6e99cf0174d22ff75 Mon Sep 17 00:00:00 2001
From: Martin Strecker <martin.strecker@sonarsource.com>
Date: Wed, 8 Jan 2025 11:19:45 +0100
Subject: [PATCH] Add benchmark

---
 rules/S1215/csharp/rule.adoc | 80 ++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)

diff --git a/rules/S1215/csharp/rule.adoc b/rules/S1215/csharp/rule.adoc
index ff4480ba20a..6afbb8fbddd 100644
--- a/rules/S1215/csharp/rule.adoc
+++ b/rules/S1215/csharp/rule.adoc
@@ -29,4 +29,84 @@ There may be exceptions to this rule: for example, you've just triggered some ev
 * https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/latency[Garbage collection latency modes]
 * https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/performance#troubleshoot-performance-issues[Garbage collection troubleshoot performance issues]
 
+=== Benchmarks
+
+Each .NET runtime features distinct implementations, modes, and configurations for its garbage collector. 
+The benchmark below illustrates how invoking `GC.Collect()` can have opposite effects across different runtimes.
+
+[options="header"]
+|===
+| Runtime              | Collect | Mean     | StdDev   | Gen1       | Gen2      | Allocated
+| .NET 9.0             | False   | 659.2 ms | 15.69 ms | 21000.0000 | 6000.0000 | 205.95 MB
+| .NET 9.0             | True    | 888.8 ms | 15.34 ms | 21000.0000 | 7000.0000 | 205.95 MB
+|                      |         |          |          |            |           |          
+| .NET Framework 4.8.1 | False   | 545.7 ms | 19.49 ms | 19000.0000 | 7000.0000 |  228.8 MB
+| .NET Framework 4.8.1 | True    | 484.8 ms | 11.79 ms | 19000.0000 | 7000.0000 |  228.8 MB
+|===
+
+==== Glossary
+
+* **Mean** Arithmetic mean of all measurements
+* **StdDev** Standard deviation of all measurements
+* **Gen1** GC Generation 1 collects per 1000 operations
+* **Gen2** GC Generation 2 collects per 1000 operations
+* **Allocated** Allocated memory per single operation (managed only, inclusive, 1KB = 1024B)
+* **1 ms** 1 Millisecond (0.001 sec)
+
+The results were generated by running the following snippet with https://github.com/dotnet/BenchmarkDotNet[BenchmarkDotNet]:
+
+[source,csharp]
+----
+class Tree
+{
+    public List<Tree> Children = new();
+}
+
+private void AppendToTree(Tree tree, int childsPerTree, int depth)
+{
+    if (depth == 0)
+    {
+        return;
+    }
+    for (int i = 0; i < childsPerTree; i++)
+    {
+        var child = new Tree();
+        tree.Children.Add(child);
+        AppendToTree(child, childsPerTree, depth - 1);
+    }
+}
+
+[Benchmark]
+[Arguments(true)]
+[Arguments(false)]
+public void Benchmark(bool collect)
+{
+    var tree = new Tree();
+    AppendToTree(tree, 8, 7);        // Create 8^7 Tree objects (2.097.152 objects) linked via List<Tree> Children
+    GC.Collect();
+    GC.Collect();                    // Move the objects to generation 2
+    AppendToTree(new Tree(), 8, 6);  // Add some more memory preasure (8^6 262.144 objects) which can be collected right after this call
+    tree = null;                     // Remove all references to the tree and its content. This freees up 8^7 Tree objects (2.097.152 objects)
+    if (collect)
+    {
+        GC.Collect();                // Force GC to run and block until it finishes
+    }
+    AppendToTree(new Tree(), 3, 10); // Do some more allocations (3^10 = 59.049)
+    AppendToTree(new Tree(), 4, 7);  // 4^10 = 1.048.576
+    AppendToTree(new Tree(), 5, 7);  // 5^7 = 78.125
+    GC.Collect(); // Collect all the memory allocated in this method
+}
+----
+
+Hardware configuration:
+
+[source]
+----
+BenchmarkDotNet v0.14.0, Windows 10 (10.0.19045.5247/22H2/2022Update)
+Intel Core Ultra 7 165H, 1 CPU, 22 logical and 16 physical cores
+  [Host]               : .NET Framework 4.8.1 (4.8.9282.0), X64 RyuJIT VectorSize=256
+  .NET 9.0             : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX2
+  .NET Framework 4.8.1 : .NET Framework 4.8.1 (4.8.9282.0), X64 RyuJIT VectorSize=256
+----
+
 include::rspecator.adoc[]
\ No newline at end of file