Scoped variables

Andrew Haley aph at
Tue Dec 4 10:39:28 UTC 2018


On 12/3/18 6:24 PM, Ron Pressler wrote:
> Yes, scope variables are indeed orthogonal to fibers (although we would like to
> combine them with structured concurrency).

> Dean Long has started working on an early prototype, which he’ll
> present hopef ully soon.

Aw, I was too late. Never mind :-)

I was looking for something interesting and reasonably self-contained
to do.

> While scope locals are certainly superior to TLs from a programming
> perspective, I’m not sure beating them on sheer performance would be
> so easy. But If you have some ideas on how to do that, they would be
> most welcome.

I'm really shocked by that. ThreadLocals are *horrible*: twelve memory
loads and two conditional branches in the best case. I see John Rose's
comments about the cost of maintaining the footprint cost of today's
ThreadLocals, but the idea of searching down the stack for a binding
isn't going to delight anyone.

I don't want to poison the well before we've seen Dean Long's
prototype, though. That would be unfair, so I'll wait.

Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <>
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671

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