从 Web API (2.1) 控制器运行 STA（单线程单元）线程

Question

我正在尝试从 Web API (2.1) 控制器运行 STA（单线程单元）线程。

为此，我使用StaTaskScheduler：

/// <summary>Provides a scheduler that uses STA threads.</summary>
public sealed class StaTaskScheduler : TaskScheduler, IDisposable
{
    /// <summary>Stores the queued tasks to be executed by our pool of STA threads.</summary>
    private BlockingCollection<Task> _tasks;
    /// <summary>The STA threads used by the scheduler.</summary>
    private readonly List<Thread> _threads;

    /// <summary>Initializes a new instance of the StaTaskScheduler class with the specified concurrency level.</summary>
    /// <param name="numberOfThreads">The number of threads that should be created and used by this scheduler.</param>
    public StaTaskScheduler(int numberOfThreads)
    {
        // Validate arguments
        if (numberOfThreads < 1) throw new ArgumentOutOfRangeException("concurrencyLevel");

        // Initialize the tasks collection
        _tasks = new BlockingCollection<Task>();

        // Create the threads to be used by this scheduler
        _threads = Enumerable.Range(0, numberOfThreads).Select(i =>
        {
            var thread = new Thread(() =>
            {
                // Continually get the next task and try to execute it.
                // This will continue until the scheduler is disposed and no more tasks remain.
                foreach (var t in _tasks.GetConsumingEnumerable())
                {
                    TryExecuteTask(t);
                }
            });
            thread.IsBackground = true;
            thread.SetApartmentState(ApartmentState.STA);
            return thread;
        }).ToList();

        // Start all of the threads
        _threads.ForEach(t => t.Start());
    }
}

一种选择是从CustomHttpControllerDispatcher 运行 STA 线程：

public static void Register(HttpConfiguration config)
{
    config.Routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }      
        //constraints: null,        
        // - Trying to avoid this
        //handler: new Controllers.CustomHttpControllerDispatcher(config)
    );
}

public class CustomHttpControllerDispatcher : System.Web.Http.Dispatcher.HttpControllerDispatcher
{
    public CustomHttpControllerDispatcher(HttpConfiguration configuration) : base(configuration)
    {
    }
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // My stuff here
    }
}

但是，这需要手动构建 http 响应，这涉及到 json 序列化，这是我宁愿避免的。

这让我有了当前的选择，即从控制器调用的库中运行 STA 线程（以生成自定义表单）。

如果使用带有Main 装饰有[STAThread] 的“Windows 应用程序”类型的测试应用程序调用该库，则一切正常。但是，当从 Web 服务控制器调用时，当以下任务返回时会出现“吞咽”异常：

注意：我没有渲染任何对话框，所以不应该有任何 “当应用程序未在 UserInteractive 模式下运行时显示模式对话框或表单不是一个有效的操作。” 异常，在从 CustomHttpControllerDispatcher 中启动的 STA 线程生成自定义表单时根本不会发生。

private Task<AClass> SendAsync1()
{
    var staTaskScheduler = new StaTaskScheduler(1);

    return Task.Factory.StartNew<CustomForm>(() =>
        {
            // - execution causes "swallowed exception"
            return new AClass();
        }, 
        CancellationToken.None,
        TaskCreationOptions.None,
        staTaskScheduler
    );
}

即单步调试时，单步调试后堆栈跟踪消失：

return new AClass(); 

我通常通过缩小一些断点来解决这个问题，但对于这种情况，我认为这是不可能的，因为 Task.cs（以及大量相关文件）没有调试符号或源代码。

注意：我现在可以逐步完成 System.Threading.Tasks 的反汇编，但是调试过程可能会很长，因为这些库不是微不足道的，因此非常感谢任何见解。

我怀疑可能是 b/c 我正在尝试从 MTA 线程（控制器）调度 STA 线程，但不是肯定的？

---

用法

GetCustomForm().Wait();


private FixedDocumentSequence _sequence;

private async Task GetCustomForm()
{
    // - will be slapped with a "calling thread cannot access...", next issue
    _sequence = await SendAsync1b();
}


private readonly StaTaskScheduler _staTaskScheduler = new StaTaskScheduler(1);

private Task<FixedDocumentSequence> SendAsync1b()
{
    //var staTaskScheduler = new StaTaskScheduler(100);
    //var staTaskScheduler = new StaTaskScheduler(1);

    return Task.Factory.StartNew<FixedDocumentSequence>(() =>
    {
        FixedDocumentSequence sequence;
        CustomForm view = new CustomForm();

        view.ViewModel = new ComplaintCustomFormViewModel(BuildingEntity.form_id, (int)Record);     
        sequence = view.ViewModel.XpsDocument.GetFixedDocumentSequence();

        return sequence;
    },
    CancellationToken.None,
    TaskCreationOptions.None,
    _staTaskScheduler);
}

参考文献

• ASP.Net WebApi STA Mode
• Custom route handlers in ASP.Net WebAPI
• https://www.c-sharpcorner.com/article/global-and-per-route-message-handlers-in-webapi/
• https://docs.microsoft.com/en-us/aspnet/web-api/overview/advanced/http-message-handlers
• https://weblog.west-wind.com/posts/2012/Sep/18/Creating-STA-COM-compatible-ASPNET-Applications

Answer 1

直接在 STA 线程中运行 WPF/Entity 代码似乎可以正常工作：

Thread thread = GetCustomFormPreviewView4();
thread.Start();
thread.Join();


private Thread GetCustomFormPreviewView4()
{
    var thread = new Thread(() =>
        {
            FixedDocumentSequence sequence;
            CustomForm view = new CustomForm();

            view.ViewModel = new ComplaintCustomFormViewModel(BuildingEntity.form_id, (int)Record);     
            sequence = view.ViewModel.XpsDocument.GetFixedDocumentSequence();

            //view.ShowDialog();
            //...
        }
    );

    thread.IsBackground = true;
    thread.SetApartmentState(ApartmentState.STA);

    return thread;
}