Question

Suppose I have a static helper class that I’m using a lot in a web app. Suppose that the app receives about 20 requests per second for a sustained period of time and that, by magic, two requests ask the static class to do some work at the exact same nanosecond.

What happens when this happens?

To provide some context, the class is a used to perform a linq-to-sql query: it receives a few parameters, including the UserID, and returns a list of custom objects.

thanks.

Answer 1

What happens when this happens?

If your methods are reentrant then they are thread safe and what will happen is that chances are they will work. If those static methods rely on some shared state and you haven’t synchronized access to this state chances are this shared state will get corrupted. But you don’t need to hit the method at the same nanosecond by 20 requests to corrupt your shared state. 2 suffice largely if you don’t synchronize it.

So static methods by themselves are not evil (well actually they are as they are not unit test friendly but that’s another topic), it’s the way they are implemented that matters in a multithreaded environment. So you should make them thread safe.

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UPDATE:

Because in the comments section you mentioned LINQ-TO-SQL as long as all variables used in the static method are local, this method is thread-safe. For example:

public static SomeEntity GetEntity(int id)
{
    using (var db = new SomeDbContext())
    {
        return db.SomeEntities.FirstOrDefault(x => x.Id == id);
    }
}