.NET 8中ChangeToken.OnChange引发栈溢出异常问题排查

在Ubuntu 24.04环境下使用.NET 8编写的文件变更监听测试，执行dotnet test时触发栈溢出异常，但相同代码在其他项目中可正常运行；注释掉ChangeToken.OnChange代码块后，测试仅因断言失败不通过，但不会崩溃。

测试代码 #

using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Primitives;
using Shouldly;

[TestFixture]
public class PhysicalFileProviderOnChangeTests
{
  private string _tempDirectory;
  private string _testFilePath;

  [SetUp]
  public void SetUp()
  {
    _tempDirectory = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
    Directory.CreateDirectory(_tempDirectory);

    _testFilePath = Path.Combine(_tempDirectory, "testfile.txt");
    File.WriteAllText(_testFilePath, "Hello, World!");

    var provider = new PhysicalFileProvider(_tempDirectory);
  }


  [Test]
  public async Task TestOnChange_Handler()
  {
    var provider = new PhysicalFileProvider(_tempDirectory);
    var changeToken = provider.Watch("testfile.txt");

    var changeDetected = false;

    ChangeToken.OnChange(
      () => changeToken,
      () => changeDetected = true
    );

    File.WriteAllText(_testFilePath, "New Content");

    await Task.Delay(100);

    changeDetected.ShouldBeTrue();
  }

  [TearDown]
  public void TearDown()
  {
    if (Directory.Exists(_tempDirectory))
    {
      Directory.Delete(_tempDirectory, true);
    }
  }
}

栈溢出异常信息 #

The active test run was aborted. Reason: Test host process crashed : Stack overflow.
Repeat 10915 times: #

at System.Threading.CancellationTokenSource.Register(System.Delegate, System.Object, System.Threading.SynchronizationContext, System.Threading.ExecutionContext)
at System.Threading.CancellationToken.Register(System.Delegate, System.Object, Boolean, Boolean)
at Microsoft.Extensions.Internal.ChangeCallbackRegistrar.UnsafeRegisterChangeCallback[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.Action1<System.Object>, System.Object, System.Threading.CancellationToken, System.Action1<System.__Canon>, System.__Canon)
at Microsoft.Extensions.Primitives.CancellationChangeToken.RegisterChangeCallback(System.Action1<System.Object>, System.Object) at Microsoft.Extensions.Primitives.ChangeToken+ChangeTokenRegistration1[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].RegisterChangeTokenCallback(Microsoft.Extensions.Primitives.IChangeToken)
at Microsoft.Extensions.Primitives.ChangeToken+ChangeTokenRegistration1[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].OnChangeTokenFired() at Microsoft.Extensions.Primitives.ChangeToken+ChangeTokenRegistration1+<>c[[System.__Canon, System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].b__7_0(System.Object)
at System.Threading.CancellationTokenSource.Invoke(System.Delegate, System.Object, System.Threading.CancellationTokenSource) #

at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean)
at Microsoft.Extensions.FileProviders.Physical.PhysicalFilesWatcher+<>c.<.cctor>b__43_0(System.Object)
at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(System.Threading.Thread, System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(System.Threading.Tasks.Task ByRef, System.Threading.Thread)
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading.PortableThreadPool+WorkerThread.WorkerThreadStart()

异常触发特征 #

• 执行dotnet test直接触发栈溢出，导致测试进程崩溃
• 相同代码在其他项目中可正常执行
• 注释掉以下代码块后，测试仅断言失败但无崩溃：

ChangeToken.OnChange(
  () => changeToken,  
  () => changeDetected = true
);

问题原因与修复方案 #

核心原因 #

ChangeToken.OnChange的第一个参数是返回新变更令牌的工厂委托，当前代码直接返回同一个changeToken实例。当文件变更触发回调后，ChangeToken.OnChange会尝试通过工厂委托获取新令牌重新注册监听，但因始终复用旧令牌，导致无限循环注册回调，最终引发栈溢出。

修复方案 #

修改工厂委托，每次调用时从PhysicalFileProvider重新获取新的变更令牌：

ChangeToken.OnChange(
  () => provider.Watch("testfile.txt"), // 每次重新获取新令牌
  () => changeDetected = true
);

额外优化点 #

1. 删除SetUp方法中未使用的PhysicalFileProvider实例，清理冗余代码
2. 使用using语句确保PhysicalFileProvider被正确释放，避免资源泄漏

修改后的完整测试代码：

using Microsoft.Extensions.FileProviders;
using Microsoft.Extensions.Primitives;
using Shouldly;

[TestFixture]
public class PhysicalFileProviderOnChangeTests
{
  private string _tempDirectory;
  private string _testFilePath;

  [SetUp]
  public void SetUp()
  {
    _tempDirectory = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
    Directory.CreateDirectory(_tempDirectory);

    _testFilePath = Path.Combine(_tempDirectory, "testfile.txt");
    File.WriteAllText(_testFilePath, "Hello, World!");
  }


  [Test]
  public async Task TestOnChange_Handler()
  {
    using var provider = new PhysicalFileProvider(_tempDirectory);
    var changeDetected = false;

    ChangeToken.OnChange(
      () => provider.Watch("testfile.txt"),
      () => changeDetected = true
    );

    File.WriteAllText(_testFilePath, "New Content");

    await Task.Delay(100);

    changeDetected.ShouldBeTrue();
  }

  [TearDown]
  public void TearDown()
  {
    if (Directory.Exists(_tempDirectory))
    {
      Directory.Delete(_tempDirectory, true);
    }
  }
}

内容的提问来源于stack exchange，提问作者Alexander Zeitler