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Monday, July 13, 2026

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13:27:40enoqso I asked about virtual threads (spring) and parallel http requests a couple days ago; turns out by default it's not parallelized (which is what I expected) https://dpaste.com/EXBWBMSAN
13:27:57enoqwhen I curl the endpoint, it waits for 20s
13:28:20enoqwhat's the recommended way to deal with that? wrap in CompletableFuture.supplyAsync?
13:29:59enoq(not 100% sure if that approach loses ThreadLocal context)
13:31:24enoqthere's also @Async btw
13:34:45Parahuh, my firewall says dpaste is a dangerous website
13:39:33enoq~pastebin list options
13:39:33javabotenoq, what does that even *mean*?
13:39:42enoq~pastebin
13:39:42javabotPlease paste your code and any errors online. For runnable classes, try https://ideone.com/ . For general code and errors, use https://gist.github.com or https://dpaste.org/
13:39:44nevetDiscover gists
13:39:55enoqdpaste.org is down
13:40:55enoqhttps://gist.github.com/BernhardPosselt/a5638b26987519fdb60b2fdd414f5443
13:40:55nevetProductController.kt
13:42:04ParaSo, it does exactly what it should?
13:42:18enoqright, I think we had another misunderstanding back then
13:42:36enoqvirtual threads don't parallelize IO in the same thread
13:42:59ParaI mean... you've literally written "wait 10 seconds, then wait 10 seconds" :)
13:43:18enoqsince I'll be aggregating a lot of different rest endpoints, this makes me wonder if I should go reactive and maybe Kotlin coroutines
13:45:09ParaThat sounds like quite a leap to conclusion. You've written synchronous code, that will not magically turn into asynchronous.
13:46:05enoqspring.threads.virtual.enabled=true btw
13:46:21enoqso it will spin off a virtual thread per request
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13:46:51enoqso it should be async, just not parallel
13:46:57ParaYou're solving the wrong problem. You need to change your programming pattern if you want async/parallel execution.
13:51:43enoqright, so this is how I understand it you could do it using servlet tech https://gist.github.com/BernhardPosselt/a5638b26987519fdb60b2fdd414f5443
13:51:43nevetProductController.kt
13:51:55enoqbasically use CompletableFuture.supplyAsync
13:52:09enoqjust not 100% sure if this makes sense
13:52:25ParaI don't see how "servlet tech" relates to this at all.
13:52:38ParaBut yeah, that's what futures are for.
13:53:06enoqservlet as in: not reactive style
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13:55:07dreamrealenoq: did you turn on virtual threads, and you're seeing *subsequent* invocation?
13:56:53enoqI did turn it on, yes
13:57:22enoqThread.currentThread().isVirtual() is true
13:57:54enoqand they're happening one after another
13:59:43dreamrealokay, so let me make sure what's being described: you have AN ENDPOINT, and you're calling it twice, AND it's executing sequentially such that a 10s call is taking 2(10)s, not 10s twice
14:00:52dreamrealyou would expect *some* deviation (the time between the "two calls" being started plus a slight deviation for wire transfer time) but those would be pretty small
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14:02:18enoqI tried to simulate 2 REST endpoints that each take 10s to respond; I want both endpoints to be called in parallel to reduce it from 20s to 10s; later on I'll need to aggregate data from various different services
14:02:44enoqif I used Thread.sleep() wrong, let me know
14:02:48dreamrealenoq: You shouldn't see sequential behavior from those servlets *even without* virtual threads
14:02:58dreamrealsomething else is going on
14:03:09enoqI'm calling the /testwait endpoint btw
14:03:32enoqfrom my understanding, Thread.sleep in a virtual thread should suspend, correct?
14:03:42dreamrealshould suspend THAT THREAD, yes
14:04:26dreamrealbut even without virtual threads you shouldn't be seeing one-after-the-other execution
14:04:48dreamrealOH
14:04:55dreamrealtestwait() is what's blocking, yeah?
14:05:22enoqyes
14:05:32dreamrealthose ARE sequential for that thread
14:05:39dreamrealyou're not executing two calls at the same time
14:05:57enoqright, that's what I was trying to communicate, we probably talked by each other
14:06:26dreamrealno worries, I'm in a meeting and attention is spread
14:06:38dreamrealso this behavior is *correct* for that code
14:06:48enoqI don't care too much about being able to serve 100k requests at once, I'm more interested in cutting down on sequential async calls
14:06:49dreamrealyou run one, then you run the other: 10s twice. That's correct and expected.
14:07:04dreamrealYou're not running those calls at the same time.
14:07:13dreamrealYour *code* doesn't run them at the same time.
14:07:38dreamrealcreate a list of completion results, then resolve them.
14:07:42enoqright, so would you still stick with servlet if that was the main thing your application did and sprinkle in CompletableFutures?
14:08:15enoqmy guess is that many requests can't be parallel because they'll depend on previous requests, but there might a good chunk that could
14:08:48dreamrealyeah, you're literally needing to spread out the calls, this is where you actually DO get to multiplex requests
14:11:29dreamrealIt's not DIFFICULT: create a set of requests and start them, then collect the results
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18:49:19sambalala -+\
18:58:32dreamrealI actually disagree
18:58:54ernimril^~!
18:59:23dreamrealno, no, you *!@
19:00:45dreamrealThou offendsth me
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23:52:55NeXeNconcurrency != parallel
23:57:26NeXeNenoq: and don't fall into the forkjoinpool trap. always lean on your StructuredTaskScope and ExecutorService https://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/StructuredTaskScope.html and https://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/ExecutorService.html btw that's loom docs. don't try and use a spliterator or something or you'll end up waiting 10 seconds blocking
23:57:27NeXeNthe rest of the world
23:57:28javabotNeXeN's titles: "StructuredTaskScope (Java SE 25 & JDK 25 [build 1])" | "ExecutorService (Java SE 25 & JDK 25 [build 1])"
23:57:29nevethttps://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/StructuredTaskScope.html "StructuredTaskScope (Java SE 25 & JDK 25 [build 1])" || https://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/ExecutorService.html "ExecutorService (Java SE 25 & JDK 25 [build 1])"