Update Dispose pattern examples to use thread-safe implementation

Co-authored-by: IEvangelist <[email protected]>

Author: Copilot

docs/standard/garbage-collection/implementing-dispose.md

@@ -91,7 +91,7 @@ All non-sealed classes (or Visual Basic classes not modified as `NotInheritable`
 
 ### Base class with managed resources
 
-Here's a general example of implementing the dispose pattern for a base class that only owns managed resources.
+Here's a general example of implementing the dispose pattern for a base class that only owns managed resources. The example uses <xref:System.Threading.Interlocked.CompareExchange%2A?displayProperty=nameWithType> to ensure thread-safe disposal.
 
 :::code language="csharp" source="../../../samples/snippets/csharp/VS_Snippets_CLR_System/system.idisposable/cs/base1.cs":::
 :::code language="vb" source="../../../samples/snippets/visualbasic/VS_Snippets_CLR_System/system.idisposable/vb/base1.vb":::
@@ -153,7 +153,7 @@ The following code demonstrates how to handle unmanaged resources by implementin
 > The behavior of the `DisposableBaseWithSafeHandle` class is equivalent to the behavior of the [`DisposableBaseWithFinalizer` class in a previous example](#base-class-with-unmanaged-resources), however the approach demonstrated here is safer:
 >
 > - There is no need to implement a finalizer, because <xref:System.Runtime.InteropServices.SafeHandle> will take care of finalization.
-> - There is no need for synchronization to guarantee thread safety. Even though there is a race condition in the `Dispose` implementation of `DisposableBaseWithSafeHandle`, <xref:System.Runtime.InteropServices.SafeHandle> guarantees that <xref:System.Runtime.InteropServices.SafeHandle.ReleaseHandle%2A?displayProperty=nameWithType> will be called only once.
+> - <xref:System.Runtime.InteropServices.SafeHandle> guarantees that <xref:System.Runtime.InteropServices.SafeHandle.ReleaseHandle%2A?displayProperty=nameWithType> will be called only once, even in multi-threaded scenarios.
 
 ### Built-in safe handles in .NET
 

docs/standard/garbage-collection/snippets/dispose-pattern/csharp/Disposable.cs

@@ -1,8 +1,13 @@
 using System;
+using System.Threading;
 
 public class Disposable : IDisposable
 {
-    private bool _disposed;
+    // Detect redundant Dispose() calls in a thread-safe manner.
+    // _disposed == 0 means Dispose(bool) has not been called yet.
+    // _disposed == 1 means Dispose(bool) has been already called.
+    private int _disposed;
+
     // <SnippetDispose>
     public void Dispose()
     {
@@ -16,21 +21,19 @@ public void Dispose()
     // <SnippetDisposeBool>
     protected virtual void Dispose(bool disposing)
     {
-        if (_disposed)
+        // In case _disposed is 0, atomically set it to 1.
+        // Enter the branch only if the original value is 0.
+        if (Interlocked.CompareExchange(ref _disposed, 1, 0) == 0)
         {
-            return;
-        }
+            if (disposing)
+            {
+                // Dispose managed state (managed objects).
+                // ...
+            }
 
-        if (disposing)
-        {
-            // Dispose managed state (managed objects).
+            // Free unmanaged resources.
             // ...
         }
-
-        // Free unmanaged resources.
-        // ...
-
-        _disposed = true;
     }
     // </SnippetDisposeBool>
 }

docs/standard/garbage-collection/snippets/dispose-pattern/vb/Disposable.vb

@@ -1,6 +1,12 @@
-Public Class Disposable : Implements IDisposable
+Imports System.Threading
+
+Public Class Disposable : Implements IDisposable
+
+    ' Detect redundant Dispose() calls in a thread-safe manner.
+    ' _disposed = 0 means Dispose(bool) has not been called yet.
+    ' _disposed = 1 means Dispose(bool) has been already called.
+    Private _disposed As Integer
 
-    Dim disposed As Boolean
     ' <SnippetDispose>
     Public Sub Dispose() _
         Implements IDisposable.Dispose
@@ -13,19 +19,17 @@
 
     ' <SnippetDisposeBool>
    Protected Overridable Sub Dispose(disposing As Boolean)
-		If disposed Then Exit Sub
-
-		If disposing Then
-
-            ' Free managed resources.
+        ' In case _disposed is 0, atomically set it to 1.
+        ' Enter the branch only if the original value is 0.
+        If Interlocked.CompareExchange(_disposed, 1, 0) = 0 Then
+            If disposing Then
+                ' Free managed resources.
+                ' ...
+            End If
+
+            ' Free unmanaged resources.
             ' ...
-
         End If
-
-        ' Free unmanaged resources.
-        ' ...
-
-        disposed = True
    End Sub
     ' </SnippetDisposeBool>
 

samples/snippets/csharp/VS_Snippets_CLR_System/system.idisposable/cs/base1.cs

@@ -1,10 +1,13 @@
 using System;
 using System.IO;
+using System.Threading;
 
 public class DisposableBase : IDisposable
 {
-    // Detect redundant Dispose() calls.
-    private bool _isDisposed;
+    // Detect redundant Dispose() calls in a thread-safe manner.
+    // _isDisposed == 0 means Dispose(bool) has not been called yet.
+    // _isDisposed == 1 means Dispose(bool) has been already called.
+    private int _isDisposed;
 
     // Instantiate a disposable object owned by this class.
     private Stream? _managedResource = new MemoryStream();
@@ -19,10 +22,10 @@ public void Dispose()
     // Protected implementation of Dispose pattern.
     protected virtual void Dispose(bool disposing)
     {
-        if (!_isDisposed)
+        // In case _isDisposed is 0, atomically set it to 1.
+        // Enter the branch only if the original value is 0.
+        if (Interlocked.CompareExchange(ref _isDisposed, 1, 0) == 0)
         {
-            _isDisposed = true;
-
             if (disposing)
             {
                 // Dispose managed state.

samples/snippets/csharp/VS_Snippets_CLR_System/system.idisposable/cs/safe.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.Runtime.InteropServices;
+using System.Threading;
 using Microsoft.Win32.SafeHandles;
 
 // Wraps the IntPtr allocated by Marshal.AllocHGlobal() into a SafeHandle.
@@ -27,8 +28,10 @@ public static LocalAllocHandle Allocate(int numberOfBytes)
 
 public class DisposableBaseWithSafeHandle : IDisposable
 {
-    // Detect redundant Dispose() calls.
-    private bool _isDisposed;
+    // Detect redundant Dispose() calls in a thread-safe manner.
+    // _isDisposed == 0 means Dispose(bool) has not been called yet.
+    // _isDisposed == 1 means Dispose(bool) has been already called.
+    private int _isDisposed;
 
     // Managed disposable objects owned by this class
     private LocalAllocHandle? _safeHandle = LocalAllocHandle.Allocate(10);
@@ -44,10 +47,10 @@ public void Dispose()
     // Protected implementation of Dispose pattern.
     protected virtual void Dispose(bool disposing)
     {
-        if (!_isDisposed)
+        // In case _isDisposed is 0, atomically set it to 1.
+        // Enter the branch only if the original value is 0.
+        if (Interlocked.CompareExchange(ref _isDisposed, 1, 0) == 0)
         {
-            _isDisposed = true;
-
             if (disposing)
             {
                 // Dispose managed state.

samples/snippets/visualbasic/VS_Snippets_CLR_System/system.idisposable/vb/base1.vb

@@ -1,10 +1,13 @@
 Imports System.IO
+Imports System.Threading
 
 Public Class DisposableBase
     Implements IDisposable
 
-    ' Detect redundant Dispose() calls.
-    Private _isDisposed As Boolean
+    ' Detect redundant Dispose() calls in a thread-safe manner.
+    ' _isDisposed = 0 means Dispose(bool) has not been called yet.
+    ' _isDisposed = 1 means Dispose(bool) has been already called.
+    Private _isDisposed As Integer
 
     ' Instantiate a disposable object owned by this class.
     Private _managedResource As Stream = New MemoryStream()
@@ -17,9 +20,9 @@ Public Class DisposableBase
 
     ' Protected implementation of Dispose pattern.
     Protected Overridable Sub Dispose(disposing As Boolean)
-        If Not _isDisposed Then
-            _isDisposed = True
-
+        ' In case _isDisposed is 0, atomically set it to 1.
+        ' Enter the branch only if the original value is 0.
+        If Interlocked.CompareExchange(_isDisposed, 1, 0) = 0 Then
             If disposing Then
                 ' Dispose managed state.
                 _managedResource?.Dispose()

samples/snippets/visualbasic/VS_Snippets_CLR_System/system.idisposable/vb/safe.vb

@@ -1,6 +1,7 @@
 Imports System
 Imports System.IO
 Imports System.Runtime.InteropServices
+Imports System.Threading
 Imports Microsoft.Win32.SafeHandles
 
 ' Wraps the IntPtr allocated by Marshal.AllocHGlobal() into a SafeHandle.
@@ -29,8 +30,10 @@ End Class
 Public Class DisposableBaseWithSafeHandle
     Implements IDisposable
 
-    ' Detect redundant Dispose() calls.
-    Private _isDisposed As Boolean
+    ' Detect redundant Dispose() calls in a thread-safe manner.
+    ' _isDisposed = 0 means Dispose(bool) has not been called yet.
+    ' _isDisposed = 1 means Dispose(bool) has been already called.
+    Private _isDisposed As Integer
 
     ' Managed disposable objects owned by this class
     Private _safeHandle As LocalAllocHandle = LocalAllocHandle.Allocate(10)
@@ -44,9 +47,9 @@ Public Class DisposableBaseWithSafeHandle
 
     ' Protected implementation of Dispose pattern.
     Protected Overridable Sub Dispose(disposing As Boolean)
-        If Not _isDisposed Then
-            _isDisposed = True
-
+        ' In case _isDisposed is 0, atomically set it to 1.
+        ' Enter the branch only if the original value is 0.
+        If Interlocked.CompareExchange(_isDisposed, 1, 0) = 0 Then
             If disposing Then
                 ' Dispose managed state.
                 _otherUnmanagedResource?.Dispose()