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 <[email protected]> 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 <[email protected]> > 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 <[email protected]> on behalf of David >> Alayachew <[email protected]> >> *Sent:* Friday, 15 August 2025 11:52 >> *To:* loom-dev <[email protected]> >> *Subject:* My experience with Structured Concurrency >> >> Hello @loom-dev <[email protected]>, >> >> 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 >> >>
