New Early Access builds

[Alan Bateman]

On 16/01/2021 16:08, Cay Horstmann wrote:
> Build 16-loom+9-316 had Scoped and LightweightThreadLocal classes, 
> which are not present in 17-loom+2-42. 
> Thread.Builder.disallowThreadLocals is also gone. What's the latest 
> thinking on thread locals and scoped variables?

The "thinking" hasn't changed. All threads support thread locals by 
default. Thread.Builder has a "noThreadLocals" method that prevents a 
thread from setting values for its copy of thread locals (it only sees 
the initial value). The builder API also has a method to opt-out of 
inheriting the initial value of Inhertiable-TLs, similar to the boolean 
parameter on the pre-existing 5-arg Thread constructor.

TLs are problematic for a number reasons, one being that they are too 
general with resulting over use. The exploratory into scope variables is 
to find a better and more performant solution for the "implicit 
parameter" use-case. Also the inheritance case where context or some 
immutable object is inherited into a tree of threads or parallel stream 
without copying values into the Thread or FJ tasks. Andrew Haley has 
been working on this topic and has a new prototype that we expect will 
go into the loom repo at some point. That will be the replacement for 
the early prototype that was Lightweight-TL.

So yes, there will be a bit of churn and API shimmer but the general 
direction, to find better alternatives for some TLs usages, continues.

-Alan