[External] : Re: My experience with Structured Concurrency

[David Alayachew]

Oh, I'm already doing that. Lol, I love STS BECAUSE nesting scopes is so
easy to do.

But that's an interesting idea. I kind of see what you mean -- maybe I am
stuffing too much logic into a single Joiner. I can't tell yet, so I guess
I'll just have to try it out and get back to you.

Thanks for the tip.


On Fri, Aug 15, 2025, 5:09 PM Viktor Klang <viktor.klang at oracle.com> wrote:

> Hi David,
>
> Thanks for the added detail, that really helps my understanding of your
> situation.
>
> Did you try/consider/evaluate nested scopes (each with different Joiner
> strategies) over composing Joiners themselves?
> And if you did, what were your findings when comparing those two different
> approaches?
>
> Cheers,
> √
>
>
> *Viktor Klang*
> Software Architect, Java Platform Group
> Oracle
> ------------------------------
> *From:* David Alayachew <davidalayachew at gmail.com>
> *Sent:* Friday, 15 August 2025 20:53
> *To:* Viktor Klang <viktor.klang at oracle.com>
> *Cc:* loom-dev <loom-dev at openjdk.org>
> *Subject:* [External] : Re: My experience with Structured Concurrency
>
> One other detail I'd like to highlight.
>
> Much like Collectors and Gatherers, there are a handful of super useful
> ones that you use everywhere, and then the rest are ad-hoc, inline ones
> where you sort of just make your own to handle a custom scenario. If you
> use streams often, you will run into those frequently, and that's why those
> factory methods are fantastic.
>
> Well, I have kind of found myself in the same position for Joiners.
> Joiners aren't as complex as Collectors and Gatherers, so there has
> certainly been less need for it. But I am also only a few weeks into using
> Joiners (though, I used STS for over a year). If I feel this strain now,
> then I feel like this experience is definitely worth sharing.
>
> On Fri, Aug 15, 2025, 2:44 PM David Alayachew <davidalayachew at gmail.com>
> wrote:
>
> Sure.
>
> Long story short, the biggest reason why STS is so useful for me is
> because it allows me to fire off a bunch of requests, and handle their
> failures and outcomes centrally. That is the single most useful feature of
> this library for me. It's also why Future.status was not so useful for me
> -- it calls get under the hood, and therefore might fail! Handling that was
> too much scaffolding.
>
> So, when someone recently challenged me to use Joiners (rather than the
> old STS preview versions I was used to), I started creating Joiners to
> handle all sorts of failure and outcomes. At first, a lot of them could be
> handled by the Joiner.awaitUntil(), where I would just check and see if the
> task failed, then handle the error. But as I got further and further along,
> I started needing to add state to my Joiners in order to get the failure
> handling that I wanted. For example, if a certain number of timeouts occur,
> cancel the scope. Well, that necessitates an AtomicNumber.
>
> Then, as the error-handling got more and more complex, I started finding
> myself making a whole bunch of copy paste, minor variations of similar
> Joiners. Which isn't bad or wrong, but started to feel some strain. Now, I
> need to jump through an inheritance chain just to see what my Joiner is
> really doing. It wasn't so bad, but I did start to feel a little uneasy.
> Bad memories.
>
> So, the solution to a problem like this is to create a Joiner factory.
> Which is essentially what I started to write before I started remembering
> how Collectors and Gatherers worked. At that point, I kind of realized that
> this is worth suggesting, which prompted me to write my original email.
>
> Like I said, not a big deal if you don't give it to me -- I can just make
> my own.
>
> But yes, that is the surrounding context behind that quote. Let me know if
> you need more details.
>
>
> On Fri, Aug 15, 2025, 9:25 AM Viktor Klang <viktor.klang at oracle.com>
> wrote:
>
> Hi David,
>
> First of all—thank you for your feedback!
>
> I'm curious to learn more about why you ended up in the situation you
> describe below, specifically about what use-cases led you into wishing for
> an augmentation to Joiner to facilitate composition.
>
> Are you able to share more details?
>
> >Which, funnily enough, led to a slightly different problem -- I found
> myself wanting an easier way to create Joiners. Since I was leaning on
> Joiners so much more heavily than I was for STS, I ended up creating many
> Joiners that do almost the same thing, with just minor variations. And
> inheritance wasn't always the right answer, as I can't inherit from
> multiple classes. Plus, most of my joiners were stateful, but I only wanted
> the non-stateful parts of it. I could do composition, but it sort of felt
> weird to delegate to multiple other Joiners.
>
> Cheers,
> √
>
>
> *Viktor Klang*
> Software Architect, Java Platform Group
> Oracle
> ------------------------------
> *From:* loom-dev <loom-dev-retn at openjdk.org> on behalf of David Alayachew
> <davidalayachew at gmail.com>
> *Sent:* Friday, 15 August 2025 11:52
> *To:* loom-dev <loom-dev at openjdk.org>
> *Subject:* My experience with Structured Concurrency
>
> Hello @loom-dev <loom-dev at openjdk.org>,
>
> I just wanted to share my experience with Structured Concurrency. I had
> actually been using it for a while now, but only recently got experience
> with the new Joiner. After trying it out, my previously stated opinion has
> changed.
>
> Overall, Structured Concurrency has been a pleasure. I'll avoid repeating
> ALL my old thoughts and just highlight the KEY details.
>
> * Structured Concurrency is excellent for complex error-handling.
> Receiving exceptions via the subtask makes all the error-handling less
> painful.
> * Structured Concurrency makes nesting scopes a breeze, a task I
> historically found very painful to do.
> * Inheritance allows me to take an existing Scope (now Joiner), and modify
> only what I need to in order to modify it for my use case. Great for
> reusing old strategies in new ways.
>
> Now for the new stuff -- having Joiner be the point of extension
> definitely proved to be the right move imo. I didn't mention this in my
> original message, but while it was easy to get a scope set up using
> inheritance, it wasn't always clear what invariants needed to be
> maintained. For example, the ensureOwnerAndJoined method. Was that
> something we needed to call when inheriting? On which methods? Just join()?
>
> The Joiner solution is comparatively simpler, which actually meant that I
> ended up creating way more Joiners, rather than only several STS'. Joiners
> invariants are obvious, and there is no ambiguity on what is expected from
> the implementor.
>
> Which, funnily enough, led to a slightly different problem -- I found
> myself wanting an easier way to create Joiners. Since I was leaning on
> Joiners so much more heavily than I was for STS, I ended up creating many
> Joiners that do almost the same thing, with just minor variations. And
> inheritance wasn't always the right answer, as I can't inherit from
> multiple classes. Plus, most of my joiners were stateful, but I only wanted
> the non-stateful parts of it. I could do composition, but it sort of felt
> weird to delegate to multiple other Joiners.
>
> Part of me kept wondering how well a factory method, similar to the ones
> for Collectors and Gatherers, might fare for Joiners.
>
> Regardless, even if we don't get that factory method, this library has
> been a pleasure, and I can't wait to properly implement this once it goes
> live.
>
> Thank you for your time and consideration.
> David Alayachew
>
>
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