A new build and a new structured concurrency API

[Remi Forax]

----- Original Message -----
> From: "Alex Otenko" <oleksandr.otenko at gmail.com>
> To: "Ron Pressler" <ron.pressler at oracle.com>
> Cc: "loom-dev" <loom-dev at openjdk.java.net>
> Sent: Mercredi 17 Novembre 2021 22:48:07
> Subject: Re: A new build and a new structured concurrency API

> Thanks for the great update.
> 
> I am trying to comprehend the implications of fork with onComplete.

Hi Alex,

> 
> The docs say onComplete may not be invoked at all. What is being saved
> here, compared to cancel() that guarantees onComplete will be invoked.

>From the doc, onComplete() is not called if the structured executor is already shutdown.

> 
> The other thing that seems odd is that onComplete is entirely
> side-effecting: it has no communication with the task that got completed
> (the task can't delegate responsibility for anything), and no communication
> with the consumer of Future (onComplete can't delegate responsibility for
> anything). Like, I borrow a connection - who's going to return it and how?
> I'd expect someone to have one last glance at the context of the Callable
> to clean up.

onComplete takes a BiConsumer which is a functional interface so the lambda can capture any context,
the same way a Callable can capture the same context.

> 
> Alex

regards,
Rémi

> 
> On Mon, 15 Nov 2021, 20:22 Ron Pressler, <ron.pressler at oracle.com> wrote:
> 
>> Hi.
>>
>> We have just published a new Early Access build of Project Loom over on
>> https://jdk.java.net/loom/
>>
>> The build is based on jdk-18+22, and now requires the --enable-preview
>> flag to
>> use Loom features (when compiling, remember to also add `--release 18`).
>>
>> The main new feature in this build is a new API for structured concurrency,
>> called StructuredExecutor. To learn more about its motivation,
>> capabilities,
>> and use, please read this JEP draft [1] and the Javadoc [2]. Pay special
>> attention to the new methods added to Future, resultNow and exceptionNow
>> [3], and how they complement StructuredExecutor. One of the most exciting
>> capabilities of StructuredExecutor is the new structured thread-dump
>> mentioned
>> in the JEP draft.
>>
>> Another new feature is the ability to use virtual threads as Cleaner
>> threads
>> [4]. We have also published a draft JEP for virtual threads [5]. The JEPs,
>> like
>> the project, are still a work in progress.
>>
>> As always, we appreciate feedback on these features from those who try
>> them.
>> Please, download the new EA and tell us about your experience.
>>
>> -- Ron
>>
>> [1]: http://openjdk.java.net/jeps/8277129
>> [2]:
>> https://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/StructuredExecutor.html
>> [3]:
>> https://download.java.net/java/early_access/loom/docs/api/java.base/java/util/concurrent/Future.html
>> [4]:
>> https://download.java.net/java/early_access/loom/docs/api/java.base/java/lang/ref/Cleaner.html
>> [5]: http://openjdk.java.net/jeps/8277131
>>