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1094

answers:

3

I have some code where I use a thread static object in C#.

[ThreadStatic]
private DataContext connection

I was wondering, in this case, what if any change would I get if I put the static modifier on the thread static context?

[ThreadStatic]
private static DataContext connection

With the first would there be one copy of the context per instance per thread, with the other only one copy per thread?

+3  A: 

In the first case it would probably be ignored, whereas in the second case you are correct, one instance per thread.

Otávio Décio
+9  A: 

The ThreadStaticAttribute is only designed to be used on static variables, as MSDN points out. If you use it on an instance variable, I suspect it will do precisely nothing.

Noldorin
Anyone aware of any documentation that describes the official policy on what it's supposed to do? If it is not supposed to be used in this way shouldn't it cause a compile error, or can attributes not cause compile errors?
Catskul
It would be great if it were a compiler error, because I've just spent a couple of hours tracking a mysterious threading-related bug, which turned out to be due to [ThreadStatic] being used on an instance field and thus having no effect...
romkyns
@romkyns same here... just nailed a bug caused by [ThreadStatic] on an instance field.
chakrit
+2  A: 

MSDN says :

Indicates that the value of a static field is unique for each thread.

So I guess you first case is incorrect... the attribute will probably be ignored

Thomas Levesque