ScopedValue structured forking/forwarding API

[Andrew Haley]

On 11/07/2025 11:57, Nikita Bobko wrote:

 > Please note that the API shape that I'm suggesting replicates
 > StructuredTaskScope, and it doesn't do anything that couldn't be already
 > achieved with the existing StructuredTaskScope API (Or I explained it
 > poorly).

I guess that Carrier.run(), ScopedValue.snapshot(), and 
Snapshot.forward() would do some sort of handshake to make sure that 
every Snapshot has been join()ed at the end of Carrier.run(). I guess 
that would work if we could figure out a sound way to do it, but at 
present we don't need to do much of this. I take your point about the 
StructuredTaskScope complications, though.

I'm hoping that at some point in the future we can get a secure form of 
try with resources, one that doesn't rely on the user to call close(), 
but that's a long way off.

Most people who have asked about capturing scoped values have wanted to 
use them in an unstructured way, but your request is quite different. 
Given that a StructuredTaskScope can work with any ThreadFactory, why do 
you need to replicate its working? What do you need to do differently?

I'm still curious about this:

 > However, it is straightforward to create a scoped value class of your
 > own that has any properties you wish, including different inheritance
 > rules. Given a ScopedValue.Carrier that binds some values, start your
 > thread with aCarrier.run(task). Would this work for you?

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer