如何在 ASP.NET Web API 中使用非线程安全的 async/await API 和模式?

Here's how a non-thread-safe API from the linked question might be used with such ThreadAffinityTaskScheduler:

// create a global instance of ThreadAffinityTaskScheduler - per web app
public static class GlobalState 
{
    public static ThreadAffinityTaskScheduler TaScheduler { get; private set; }

    public static GlobalState 
    {
        GlobalState.TaScheduler = new ThreadAffinityTaskScheduler(
            numberOfThreads: 10);
    }
}

// ...

// run a task which uses non-thread-safe APIs
var result = await GlobalState.TaScheduler.Run(() => 
{
    using (var dataContext = new DataContext())
    {
        var something = await dataContext.someEntities.FirstOrDefaultAsync(e => e.Id == 1);
        var morething = await dataContext.someEntities.FirstOrDefaultAsync(e => e.Id == 2);
        // ... 
        // transform "something" and "morething" into thread-safe objects and return the result
        return data;
    }
}, CancellationToken.None);

我继续实现了ThreadAffinityTaskScheduler 作为概念证明，基于 Stephen Toub 的优秀 StaTaskScheduler.ThreadAffinityTaskScheduler 维护的池线程不是经典 COM 意义上的 STA 线程，但它们确实实现了 await 延续的线程亲和性(SingleThreadSynchronizationContext 负责为此).

I went ahead and implemented ThreadAffinityTaskScheduler as a proof of concept, based on the Stephen Toub's excellent StaTaskScheduler. The pool threads maintained by ThreadAffinityTaskScheduler are not STA thread in the classic COM sense, but they do implement thread affinity for await continuations (SingleThreadSynchronizationContext is responsible for that).

到目前为止，我已经将此代码作为控制台应用程序进行了测试，它似乎可以按设计工作.我还没有在 ASP.NET 页面中对其进行测试.我没有很多生产 ASP.NET 开发经验，所以我的问题是:

So far, I've tested this code as console app and it appears to work as designed. I haven't tested it inside an ASP.NET page yet. I don't have a lot of production ASP.NET development experience, so my questions are:

1. 在 ASP.NET 中对非线程安全 API 的简单同步调用使用这种方法是否有意义(主要目标是避免牺牲可伸缩性)?

1. Does it make sense to use this approach over simple synchronous invocation of non-thread-safe APIs in ASP.NET (the main goal is to avoid sacrificing scalability)?

除了使用同步 API 调用或完全避免使用这些 API 之外，还有其他方法吗?

Is there alternative approaches, besides using synchronous API invocations or avoiding those APis at all?

有没有人在 ASP.NET MVC 或 Web API 项目中使用过类似的东西并准备分享他/她的经验?

Has anyone used something similar in ASP.NET MVC or Web API projects and is ready to share his/her experience?

关于如何使用 ASP.NET 对这种方法进行压力测试和分析的任何建议都是感激不尽.

Any advice on how to stress-test and profile this approach with ASP.NET would be appreciated.

推荐答案

Entity Framework 将(应该)处理跨 await 点的线程跳转就好了；如果不是，那么这是 EF 中的一个错误.OTOH，OperationContextScope 基于 TLS，不是 await-安全的.

Entity Framework will (should) handle thread jumps across await points just fine; if it doesn't, then that's a bug in EF. OTOH, OperationContextScope is based on TLS and is not await-safe.

1.同步 API 维护您的 ASP.NET 上下文；这包括在处理过程中通常很重要的用户身份和文化等内容.此外，许多 ASP.NET API 假设它们在实际的 ASP.NET 上下文中运行(我的意思不是只使用 HttpContext.Current；我的意思是实际上假设 SynchronizationContext.Current 是 AspNetSynchronizationContext 的一个实例.

1. Synchronous APIs maintain your ASP.NET context; this includes things such as user identity and culture that are often important during processing. Also, a number of ASP.NET APIs assume they are running on an actual ASP.NET context (I don't mean just using HttpContext.Current; I mean actually assuming that SynchronizationContext.Current is an instance of AspNetSynchronizationContext).

2-3.我使用 我自己的单线程上下文 直接嵌套在 ASP.NET 上下文中，试图让 async MVC 子操作工作 而不必复制代码.但是，您不仅失去了可扩展性优势(至少对于请求的那部分)，而且假设它们在 ASP.NET 上下文中运行，您还会遇到 ASP.NET API.

2-3. I have used my own single-threaded context nested directly within the ASP.NET context, in attempts to get async MVC child actions working without having to duplicate code. However, not only do you lose the scalability benefits (for that part of the request, at least), you also run into the ASP.NET APIs assuming that they're running on an ASP.NET context.

所以，我从未在生产中使用过这种方法.我只是在必要时使用同步 API.

So, I have never used this approach in production. I just end up using the synchronous APIs when necessary.

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