Will a request in IIS run on a single thread?

Question

We have a system that runs in IIS.

The system should always run using the same \"culture\", but we cannot rely on the server settings being set correct.

One

Answer 1

No. ASP.NET exhibits thread agility - in some situations, the request may move from one thread to another at specific points in its request lifecycle. (It's not "just anywhere"; this blog post gives more specific details.)

Unfortunately this isn't as clearly documented as it might be, and it's relatively hard to provoke - so you can easily get into the situation where under test loads, all is fine - but in production things go wrong.

However, some tests I ran a while ago (look for "jskeet" within the page) suggests that Thread.CurrentCulture is preserved even when thread agility kicks in.

Answer 2

As others pointed out, ASP.NET might decide to process parts of the same request in different threads. However, you are talking about initializing thread-static stuff at the beginning of each method, so this restriction does not apply to you: I'm quite sure that ASP.NET cannot change the current thread in the middle of one of your methods, so your approach should be fine.

Answer 3

If you know you want the culture to stay the same for all threads, then that should be a fine approach.

However, if you need to set the culture on, say, a per-request basis that may be different from one request to the next, that can potentially not be a reliable approach. Under high load, we have seen threads reused for multiple requests and requests migrated from one thread to another, leaving their culture (and other threadstatic info) behind.

Answer 4

Do you dynamically change the culture? If not, you can set the culture in the web.config file.

<system.web>
  <globalization culture="ja-JP" uiCulture="zh-HK" />
</system.web>

You can also set it at page level:

<%@Page Culture="fr-FR" Language="C#" %>

And on the thread:

Thread.CurrentThread.CurrentCulture = new CultureInfo("de-DE");

But for what you are using, the page-level or web.config level seems like the most appropriate perhaps.