From 851e6cbcb4a72f8b0e4dc77d17d723bf7510fc59 Mon Sep 17 00:00:00 2001
From: Vladimir Pecanac <vladimir.pecanac@gmail.com>
Date: Sun, 25 Oct 2026 13:17:17 +0100
Subject: [PATCH] ReaderWriterLockSlim sample: .NET 10, Lock field, async
 pitfall demo, recursion tests

---
 .../ReaderWriterLockSlimReadWriteTests.cs     | 35 +++++++++++++++++++
 .../Tests/Tests.csproj                        | 10 +++---
 .../AsyncPitfall.cs                           | 26 ++++++++++++++
 .../LockReadWrite.cs                          |  2 +-
 .../Program.cs                                |  4 ++-
 .../ReaderWriterLockSlimReadWrite.cs          |  4 +--
 ...eaderWriterLockSlimOverLockInCSharp.csproj |  2 +-
 7 files changed, 73 insertions(+), 10 deletions(-)
 create mode 100644 csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/AsyncPitfall.cs

diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/ReaderWriterLockSlimReadWriteTests.cs b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/ReaderWriterLockSlimReadWriteTests.cs
index 4ccc2bd5f8..5d404cd87a 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/ReaderWriterLockSlimReadWriteTests.cs
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/ReaderWriterLockSlimReadWriteTests.cs
@@ -48,4 +48,39 @@ public void WhenReadOrAdd_ListCountIsEqualOne()
 
         Assert.AreEqual(1, readerWriterLockSlimReadWrite.ListOfNumbers.Count);
     }
+
+    [TestMethod]
+    public void WhenReadLockIsEnteredTwiceWithDefaultPolicy_ThrowsLockRecursionException()
+    {
+        using var readerWriterLockSlim = new ReaderWriterLockSlim();
+        readerWriterLockSlim.EnterReadLock();
+
+        Assert.ThrowsExactly<LockRecursionException>(() => readerWriterLockSlim.EnterReadLock());
+
+        readerWriterLockSlim.ExitReadLock();
+    }
+
+    [TestMethod]
+    public void WhenReadLockIsEnteredTwiceWithSupportsRecursion_RecursiveReadCountIsTwo()
+    {
+        using var readerWriterLockSlim = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
+        readerWriterLockSlim.EnterReadLock();
+        readerWriterLockSlim.EnterReadLock();
+
+        Assert.AreEqual(2, readerWriterLockSlim.RecursiveReadCount);
+
+        readerWriterLockSlim.ExitReadLock();
+        readerWriterLockSlim.ExitReadLock();
+    }
+
+    [TestMethod]
+    public void WhenReadLockHolderEntersWriteLock_ThrowsLockRecursionException()
+    {
+        using var readerWriterLockSlim = new ReaderWriterLockSlim();
+        readerWriterLockSlim.EnterReadLock();
+
+        Assert.ThrowsExactly<LockRecursionException>(() => readerWriterLockSlim.EnterWriteLock());
+
+        readerWriterLockSlim.ExitReadLock();
+    }
 }
\ No newline at end of file
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/Tests.csproj b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/Tests.csproj
index 9cf18106a8..adeebb80fb 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/Tests.csproj
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/Tests/Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -10,10 +10,10 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.6.0" />
-    <PackageReference Include="MSTest.TestAdapter" Version="2.2.10" />
-    <PackageReference Include="MSTest.TestFramework" Version="2.2.10" />
-    <PackageReference Include="coverlet.collector" Version="3.2.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
+    <PackageReference Include="MSTest.TestAdapter" Version="4.5.1" />
+    <PackageReference Include="MSTest.TestFramework" Version="4.5.1" />
+    <PackageReference Include="coverlet.collector" Version="10.1.0" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/AsyncPitfall.cs b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/AsyncPitfall.cs
new file mode 100644
index 0000000000..211c8347ac
--- /dev/null
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/AsyncPitfall.cs
@@ -0,0 +1,26 @@
+namespace WhenToUseReaderWriterLockSlimOverLockInCSharp;
+
+public static class AsyncPitfall
+{
+    public static async Task<string> ExitWriteLockAfterAwait()
+    {
+        var readerWriterLockSlim = new ReaderWriterLockSlim();
+        var threadBefore = Environment.CurrentManagedThreadId;
+
+        readerWriterLockSlim.EnterWriteLock();
+        await Task.Delay(50);
+        var threadAfter = Environment.CurrentManagedThreadId;
+
+        try
+        {
+            readerWriterLockSlim.ExitWriteLock();
+
+            return $"Exited on the same thread ({threadBefore}).";
+        }
+        catch (SynchronizationLockException ex)
+        {
+            return $"{ex.GetType().Name} on thread {threadAfter} " +
+                $"(entered on thread {threadBefore}): {ex.Message}";
+        }
+    }
+}
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/LockReadWrite.cs b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/LockReadWrite.cs
index 703bb54604..27a0f651e1 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/LockReadWrite.cs
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/LockReadWrite.cs
@@ -2,7 +2,7 @@
 
 public class LockReadWrite : BaseReaderWriter
 {
-    private static readonly object LockObject = new();
+    private static readonly Lock LockObject = new();
 
     public override void AddNumbersToList(int writerExecutionsCount, int writerExecutionDelay)
     {
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/Program.cs b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/Program.cs
index 1c0575bb46..c5aa167508 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/Program.cs
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/Program.cs
@@ -18,4 +18,6 @@
 
 var readerWriterLockSlimReadWrite = new ReaderWriterLockSlimReadWrite();
 Console.WriteLine($"ReaderWriterLockSlim execution time: " +
-    $"{readerWriterLockSlimReadWrite.Execute(config)} milliseconds.");
\ No newline at end of file
+    $"{readerWriterLockSlimReadWrite.Execute(config)} milliseconds.");
+
+Console.WriteLine(await AsyncPitfall.ExitWriteLockAfterAwait());
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/ReaderWriterLockSlimReadWrite.cs b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/ReaderWriterLockSlimReadWrite.cs
index e32378f0a8..51d5d111b6 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/ReaderWriterLockSlimReadWrite.cs
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/ReaderWriterLockSlimReadWrite.cs
@@ -45,12 +45,12 @@ public override void ReadListCount(int readerExecutionsCount, int readerExecutio
 
     public void ReadOrAdd(int writerExecutionDelay)
     {
-        var random = Random.Shared.Next(0, NumbersList.Count);
-
         ReaderWriterLockSlim.EnterUpgradeableReadLock();
 
         try
         {
+            var random = Random.Shared.Next(0, NumbersList.Count);
+
             if (!NumbersList.Contains(random))
             {
                 ReaderWriterLockSlim.EnterWriteLock();
diff --git a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp.csproj b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp.csproj
index f02677bf64..dfb40caafc 100644
--- a/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp.csproj
+++ b/csharp-intermediate-topics/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp/WhenToUseReaderWriterLockSlimOverLockInCSharp.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>