Benchmark test for Append and Prepend

Rx.NET/Source/benchmarks/Benchmarks.System.Reactive/AppendPrependBenchmark.cs

@@ -0,0 +1,88 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Linq;
+using System.Threading;
+using BenchmarkDotNet.Attributes;
+
+namespace Benchmarks.System.Reactive
+{
+    [MemoryDiagnoser]
+    public class AppendPrependBenchmark
+    {
+        [Params(1, 10, 100, 1000, 10000)]
+        public int N;
+
+        int _store;
+
+        [Benchmark(Baseline = true)]
+        public void StartWithArray()
+        {
+            var array = new int[2 * N];
+            var max = 2 * N - 1;
+
+            for (var i = 0; i < N; i++)
+            {
+                array[i] = i;
+                array[max - i] = i;
+            }
+
+            Observable
+                .Empty<int>()
+                .StartWith(array)
+                .Subscribe(v => Volatile.Write(ref _store, v));
+        }
+
+        [Benchmark]
+        public void StartWithList()
+        {
+            var list = new List<int>();
+
+            for (var i = 0; i < N; i++)
+            {
+                list.Insert(i, 0);
+                list.Add(i);
+            }
+
+            Observable
+                .Empty<int>()
+                .StartWith(list)
+                .Subscribe(v => Volatile.Write(ref _store, v));
+        }
+
+        [Benchmark]
+        public void StartWithLinkedList()
+        {
+            var list = new LinkedList<int>();
+
+            for (var i = 0; i < N; i++)
+            {
+                list.AddFirst(i);
+                list.AddLast(i);
+            }
+
+            Observable
+                .Empty<int>()
+                .StartWith(list)
+                .Subscribe(v => Volatile.Write(ref _store, v));
+        }
+
+        [Benchmark]
+        public void AppendPrepend()
+        {
+            var obs = Observable.Empty<int>();
+
+            for (var i = 0; i < N; i++)
+            {
+                obs = obs.Prepend(0);
+                obs = obs.Append(0);
+            }
+
+            obs.Subscribe(v => Volatile.Write(ref _store, v));
+        }
+    }
+}

Rx.NET/Source/benchmarks/Benchmarks.System.Reactive/Program.cs

@@ -16,7 +16,8 @@ namespace Benchmarks.System.Reactive
                 typeof(CombineLatestBenchmark),
                 typeof(SwitchBenchmark),
                 typeof(BufferCountBenchmark),
-                typeof(RangeBenchmark)
+                typeof(RangeBenchmark),
+                typeof(AppendPrependBenchmark)
             });
 
             switcher.Run();