Make use of CompletionStage#handle instead of whenComplete

[He-Pin]

Which has better performance.
line/armeria#1596

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[chemicL]

@He-Pin thank you for the proposal, looks like a good perf improvement.
@OlegDokuka assuming this gets merged to 3.4.x, will this need to be forward-merged to main or is the lazy implementation completely different and should rather be a separate PR?

[OlegDokuka]

@chemicL this should be forwardmerged. Lazy one uses same method as well

[chemicL]

I just noticed #3222 which addresses the issue on main. I suppose we'll need to forward-merge but discard the change and take the one from the other PR instead.

[He-Pin]

@chemicL Yes ,I created two PR, one for 3.4.x and one for main, I saw @OlegDokuka did more optimizations of memory usage on the current main branch:)
This is my first time contribution, thanks for any guidence.

[OlegDokuka]

@He-Pin second is going to be closed since we use forward merge to keep both branches connected

[He-Pin]

But in the second one, you fold the BiConsumer to MonoCompletionStageSubscription. so I do it in a separated PR. or will you backport that memory optimization to 3.4.x?
@OlegDokuka so it's not the same pr.

[He-Pin]

jmh:run -i 5 -wi 5 -f1 -t1 .CompletionStageBenchmark.

package bench

import org.openjdk.jmh.annotations._

import java.util.concurrent.CompletableFuture
import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit

@State(Scope.Benchmark)
@OutputTimeUnit(TimeUnit.SECONDS)
@BenchmarkMode(Array(Mode.Throughput))
class CompletionStageBenchmark {
  val ex = new RuntimeException("ex")

  @Benchmark
  def benchWhenCompleteFailedSync(): Unit = {
    val future = new CompletableFuture[Int]()
    future.completeExceptionally(ex)
    val latch = new CountDownLatch(1)
    future.whenComplete((_, _) => latch.countDown())
    latch.await()
  }

  @Benchmark
  def benchWhenCompleteSuccessSync(): Unit = {
    val future = new CompletableFuture[Int]()
    future.complete(1)
    val latch = new CountDownLatch(1)
    future.whenComplete((_, _) => latch.countDown())
    latch.await()
  }

  @Benchmark
  def benchHandleFailedSync(): Unit = {
    val future = new CompletableFuture[Int]()
    future.completeExceptionally(ex)
    val latch = new CountDownLatch(1)
    future.handle((_, _) => latch.countDown())
    latch.await()
  }

  @Benchmark
  def benchHandleSuccessSync(): Unit = {
    val future = new CompletableFuture[Int]()
    future.complete(1)
    val latch = new CountDownLatch(1)
    future.handle((_, _) => latch.countDown())
    latch.await()
  }

}

[reactorbot]

@simonbasle this PR seems to have been merged on a maintenance branch, please ensure the change is merge-forwarded to intermediate maintenance branches and up to main 🙇