ScopedValue polyfill follow-up [try-with-resources]

[Andrew Haley]

On 3/31/25 23:19, Davor Hrg wrote:

> makeCurrent is not my naming :) ... it is from OpenTelemetry.
> 
> my interest in try catch version is because I saw it in OT, but I can live without that variant.
> 
> I am trying to integrate ScopedValue  patterns into my projects, and am a bit worried it will be in preview in Java 25,
> So I am trying to make something for myself to be easily replaceable by ScopedValues after it is official (not preview).

If you really need to support some property in a try-with-resources
context, you can do this:

     private static ThreadLocal<T> CONTEXT;
     private static ScopedValue<T> MY_SV;

     void makeCurrent(T t) {
         CONTEXT.set(t);
     }

     void apiEntryPoint() {
         where(MY_SV, CONTEXT.get()).call(() -> ... stuff ...);
     }

That is to say, you can use a thread-local variable to bootstrap a
scoped value, and all callees use the scoped value. This would work
well with structured concurrency.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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