Update Dispose pattern examples to use thread-safe implementation

[Copilot]

Summary

This PR updates selected Dispose pattern code examples in the documentation to use thread-safe implementations, addressing concerns raised in issue #44841 about thread safety in modern multi-threaded C# applications.

Problem

The original issue pointed out that today's C# code is typically multi-threaded and async, yet several of the Dispose pattern examples in the documentation were using simple boolean flags for disposal tracking, which is not thread-safe:

private bool _disposed;

protected virtual void Dispose(bool disposing)
{
    if (!_disposed)  // ⚠️ Not thread-safe - race condition possible
    {
        _disposed = true;
        // cleanup code...
    }
}

In a multi-threaded scenario, two threads could both evaluate !_disposed as true simultaneously, leading to double disposal attempts.

Solution

Updated specific Dispose pattern examples to use Interlocked.CompareExchange for atomic disposal detection:

private int _disposed;  // 0 = not disposed, 1 = disposed

protected virtual void Dispose(bool disposing)
{
    // Atomically set to 1 only if currently 0
    if (Interlocked.CompareExchange(ref _disposed, 1, 0) == 0)
    {
        // cleanup code - guaranteed to execute only once
    }
}

This approach ensures that even if multiple threads call Dispose() simultaneously, the cleanup code will execute exactly once in a thread-safe manner.

Files Changed

• Code Examples (C# and VB):

  • base1.cs / base1.vb - Base class with managed resources (updated to thread-safe)
  • safe.cs / safe.vb - SafeHandle implementation example (updated to thread-safe)

• Documentation:

  • implementing-dispose.md - Updated explanatory text to clarify the thread-safety approach

Note: The introductory Disposable.cs / Disposable.vb examples remain with the simpler, non-thread-safe pattern to provide an easier initial introduction. The thread-safe implementation is demonstrated in the more advanced examples later in the article (base1.cs, base2.cs, and safe.cs). The base2.cs / base2.vb examples (base class with unmanaged resources and finalizer) already used the thread-safe pattern and were not modified.

Testing

• ✅ All C# projects compile successfully
• ✅ All Visual Basic projects compile successfully
• ✅ CodeQL security analysis completed with no issues

Related Issue

Fixes #44841

Co-authored-by: IEvangelist [email protected]

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Thread Safety</issue_title>
<issue_description>Today's C# code is typically multi-threaded and async virtually everything. The Dispose pattern snippet that Visual Studio uses and you have copied for this blog post is not thread safe. Please update it with a version that is.

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 572ef6c6-5066-4a14-76a0-c3fb4b62e604
• Version Independent ID: 9c754da1-c234-fb12-580b-0fcf9ffe2c20
• Content: Implement a Dispose method
• Content Source: docs/standard/garbage-collection/implementing-dispose.md
• Product: dotnet-fundamentals
• GitHub Login: @gewarren
• Microsoft Alias: gewarren

---

Associated WorkItem - 44841</issue_description>

<agent_instructions>Please read through all comments, and take the appropriate action to address this issue.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@gewarren @IEvangelist do you want to take this one? Maybe you can make yourself the author of this article? @IEvangelist A piece of code is thread-safe if it functions correctly during simultaneous execution by multiple threads. The `Dispose` method should be idempotent, thus no matter what thread is calling it, or no matter how many times you execute them, you achieve the same result. This is a non-issue.

Fixes #26503

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Internal previews

📄 File	🔗 Preview link
docs/standard/garbage-collection/implementing-dispose.md	docs/standard/garbage-collection/implementing-dispose

[IEvangelist]

Hey @copilot - please revert the two changes to the first introduction to the pattern. We only need to show the thread-safe stuff later in the article, you can undo:

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

[Copilot]

Hey @copilot - please revert the two changes to the first introduction to the pattern. We only need to show the thread-safe stuff later in the article, you can undo:

• docs/standard/garbage-collectio...

Reverted both files to their original non-thread-safe pattern. The thread-safe examples remain in base1.cs, base2.cs, and safe.cs later in the article. (commit: a1b2c3d)

[Copilot]

Pull Request Overview

This PR updates the Dispose pattern examples in .NET documentation to use thread-safe implementations with Interlocked.CompareExchange, addressing concerns about race conditions in multi-threaded scenarios. The change replaces simple boolean flags with integer-based atomic operations to ensure disposal logic executes exactly once.

Key Changes:

• Updated disposal tracking from bool _isDisposed to int _isDisposed with atomic operations
• Added System.Threading namespace imports to all affected code files
• Enhanced comments to clarify the thread-safety approach and explain the integer field values

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

File	Description
base1.cs / base1.vb	Updated base class example to use Interlocked.CompareExchange for thread-safe disposal
safe.cs / safe.vb	Updated SafeHandle example to use Interlocked.CompareExchange for thread-safe disposal
implementing-dispose.md	Added documentation explaining the thread-safe implementation approach

[Copilot]

The updated bullet point removes important context about why synchronization is unnecessary when using SafeHandle. The original text explained that despite a race condition in the Dispose implementation, SafeHandle provides its own thread-safety guarantees. Consider revising to: '- The Dispose implementation uses xref:System.Threading.Interlocked.CompareExchange%2A?displayProperty=nameWithType to ensure thread-safe disposal. Additionally, 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.' This maintains the educational value by explaining both the explicit thread-safety in the Dispose pattern and the built-in SafeHandle protections.

Suggested change

	> - <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.
	> - The `Dispose` implementation uses <xref:System.Threading.Interlocked.CompareExchange%2A?displayProperty=nameWithType> to ensure thread-safe disposal. Additionally, <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.

[BillWagner]

I agree with this rewording. What do you think @gewarren ?

[BillWagner]

This LGTM. I like the suggested update from Copilot, but it is optional.

[BillWagner]

I agree with this rewording. What do you think @gewarren ?