Async-Await in Vertx with Project Loom

[August Nagro]

To make the sequential Async-Await code parallel, we could define a method
'awaitAll' (which is probably be a good addition to the library):

public static <A> List<A> awaitAll(List<CompletionStage<A>> stages) {
  return stages.stream().map(stage -> await(stage)).toList();
}

And change the sequential part from

  List<String> userNames = userIds.stream()
    .map(id -> await(userNamesFromSomeApi(id)))
    .toList();


To:

  List<String> userNames = awaitAll(
    userIds.stream()
      .map(id -> userNamesFromSomeApi(id))
      .toList()
  );

To make the CompletableFuture example sequential, we could make a chain of
thenCompose operations. So From:

List<CompletableFuture<String>> userNameFutures = userIds.stream()
  .map(id -> userNamesFromSomeApi(id))
  .map(CompletionStage::toCompletableFuture)
  .toList();

CompletableFuture.allOf(userNameFutures.toArray(new CompletableFuture[0]))
  .thenCompose(voidd -> {...});

To:

CompletionStage<List<String>> userNames =
  CompletableFuture.supplyAsync(() -> new ArrayList<>());

for (Long userId : userIds) {
  userNames = userNames.thenCompose(list -> {
    return userNamesFromSomeApi(userId)
      .thenApply(userName -> {
        list.add(userName);
        return list;
      });
  });
}

userNames.thenCompose(...)

Overall, I think async-await is nicer than flatMap/thenCompose chains. And
'just blocking' on a virtual thread is even nicer.


On Fri, Oct 22, 2021 at 7:26 AM Alex Otenko <oleksandr.otenko at gmail.com>
wrote:

> That example doesn't appear to be comparable.
>
> CompletableFuture example is parallel, async/await is sequential.
>
> It would be great to see the amount of boilerplate needed to implement
> both in both cases.
>
> Alex
>
> On Mon, 18 Oct 2021, 04:15 August Nagro, <augustnagro at gmail.com> wrote:
>
>> Hello; I recently implemented async/await in Vertx using Project Loom.
>>
>> Feedback and code review are very welcome. The project is only about 100
>> lines of code. Hopefully something similar could be merged into
>> `vertx-core` when Loom is released.
>>
>> https://github.com/AugustNagro/vertx-loom
>>
>> Cheers,
>>
>> August
>>
>