C# 多线程测试中的空引用

我一直在通过NHibernate网站来实现UnitOfWork模式，但我遇到了一个无法解决的问题。在第3节中，实现是线程安全的，有一个测试抛出空引用异常。我没有多线程方面的经验，所以我不知道如何在这里继续

你能告诉我是什么问题吗

测试代码

private ManualResetEvent _event;

[Test]
public void Local_data_is_thread_local()
{
    Console.WriteLine("Starting in main thread {0}", Thread.CurrentThread.ManagedThreadId);
    Local.Data["one"] = "This is a string";
    Assert.AreEqual(1, Local.Data.Count);

    _event = new ManualResetEvent(false);
    var backgroundThread = new Thread(RunInOtherThread);
    backgroundThread.Start();

    // give the background thread some time to do its job
    Thread.Sleep(100); <<<<<<< ######## EXCEPTION AFTER THIS LINE #########
    // we still have only one entry (in this thread)
    Assert.AreEqual(1, Local.Data.Count);

    Console.WriteLine("Signaling background thread from main thread {0}", Thread.CurrentThread.ManagedThreadId);
    _event.Set();
    backgroundThread.Join();
}

private void RunInOtherThread()
{
    Console.WriteLine("Starting (background-) thread {0}", Thread.CurrentThread.ManagedThreadId);
    // initially the local data must be empty for this NEW thread!
    Assert.AreEqual(0, Local.Data.Count);
    Local.Data["one"] = "This is another string";
    Assert.AreEqual(1, Local.Data.Count);

    Console.WriteLine("Waiting on (background-) thread {0}", Thread.CurrentThread.ManagedThreadId);
    _event.WaitOne();
    Console.WriteLine("Ending (background-) thread {0}", Thread.CurrentThread.ManagedThreadId);
}

问题在于：

[ThreadStatic]
private static Hashtable _localData = new Hashtable();

指示每个线程的

\u localData

字段的值是唯一的。但是，初始化只在类型构造函数中执行一次，因此只有在其上执行类型构造函数的线程具有非null的

\u localData

。所有其他线程都将具有

null

从上面链接的MSDN站点：

不要为标记有ThreadStaticAttribute的字段指定初始值，因为此类初始化仅在类构造函数执行时发生一次，因此只影响一个线程。如果未指定初始值，则如果字段是值类型，则可以将其初始化为默认值；如果字段是引用类型，则可以将其初始化为null

---

我懂了。谢谢所以改为这样做：

[ThreadStatic]私有静态哈希表\u localData；私有静态哈希表localData{get{if（_localData==null）{u localData=new Hashtable（）；}返回_localData；}}

@brainbolt是的，那会有用的。

Run started: C:\Users\brainbolt\Documents\GitHub\NHibernateUnitOfWork\NHinbernateUnitOfWork.Testing\bin\Debug\NHinbernateUnitOfWork.Testing.dll
Starting in main thread 18
Starting (background-) thread 19
System.NullReferenceException: Object reference not set to an instance of an object.
   at NHibernateUnitOfWork.NHibernateUnitOfWork.Local.LocalData.get_Count() in c:\Users\brainbolt\Documents\GitHub\NHibernateUnitOfWork\NHibernateUnitOfWork\Local.cs:line 37
   at NHinbernateUnitOfWork.Testing.LocalData_Fixture.RunInOtherThread() in c:\Users\brainbolt\Documents\GitHub\NHibernateUnitOfWork\NHinbernateUnitOfWork.Testing\LocalData_Fixture.cs:line 73
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()
   at NHibernateUnitOfWork.NHibernateUnitOfWork.Local.LocalData.get_Count() in c:\Users\brainbolt\Documents\GitHub\NHibernateUnitOfWork\NHibernateUnitOfWork\Local.cs:line 37
   at NHinbernateUnitOfWork.Testing.LocalData_Fixture.RunInOtherThread() in c:\Users\brainbolt\Documents\GitHub\NHibernateUnitOfWork\NHinbernateUnitOfWork.Testing\LocalData_Fixture.cs:line 73
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()
Signaling background thread from main thread 18
NUnit VS Adapter 2.0.0.0 executing tests is finished

[ThreadStatic]
private static Hashtable _localData = new Hashtable();