On Thu, Apr 3, 2008 at 7:01 PM, John Rose <[EMAIL PROTECTED]> wrote:

>  Yes.  You can then cast it to the subclass and go on from there.

That's what I had hoped, but the JLS doesn't actually seem to guarantee this.

>  > If so, that provides a different approach
>  > to thread-local state, where the state is held in the instance
>  > variables of MyThread objects, and the JVM is used to thread them
>  > through :-) the code until the point where they're needed.
>
>  That's how Java thread locals are implemented in the JVM.

I don't understand how that can be, as I can create as many
ThreadLocals as I want.  They can't all fit in the Thread object,
surely.  And how can reference to them be fast if they have to
indirect through a Thread subclass object?

>  You can only use this approach if (a) you control the creation of the
>  thread and can specify your own subclass for it,

That's what I had in mind.

>  You might be interested to know that Hotspot intrinsifies
>  Thread.currentThread to a couple of instructions; it's cheap.  We did
>  that to make things like thread locals efficient.

Good.

-- 
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