Fix Incorrect Calculation of Cumulative Demand in Duplicator

[minwoox]

Motivation:
The cumulative demand in a duplicator is mistakenly calculated, causing it to reach the maximum value incorrectly.

Modifications:

• Corrected the calculation logic for cumulative demand in the duplicator.

Result:

• The cumulative demand in a duplicator is correctly calculated.

[github-actions]

🔍 Build Scan® (commit: d37b734)

Job name	Status	Build Scan®
build-ubicloud-standard-16-jdk-8	✅	https://ge.armeria.dev/s/qjco5bnmaz3fi
build-ubicloud-standard-16-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/k4uvlhcrnqqgo
build-ubicloud-standard-16-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/u2srxrhohfiui
build-ubicloud-standard-16-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/mvd3uxmktrf6m
build-ubicloud-standard-16-jdk-17-leak	✅	https://ge.armeria.dev/s/3fixn3th737hu
build-ubicloud-standard-16-jdk-11	✅	https://ge.armeria.dev/s/52gy3uff47syu
build-macos-latest-jdk-21	✅	https://ge.armeria.dev/s/x67bx7nlrc5ya

[ikhoon]

Thanks!

[ikhoon]

Question) Shouldn’t we take multi-threaded race conditions into account? I might not have a complete understanding of DownstreamSubscription’s threading model.

[minwoox]

Isn't it okay because cumulativeDemand is calculated by the thread who calls the subscription.request()?

[ikhoon]

I see. If subscription.request() should be sequentically called, is it safe to remove the following lines? It seems like requestedDemand is always less than cumulativeDemand in doRequestDemand(). If I'm wrong, may I know when it could happen?

armeria/core/src/main/java/com/linecorp/armeria/common/stream/DefaultStreamMessageDuplicator.java

Lines 338 to 340 in eb7e451

	if (cumulativeDemand <= requestedDemand) {
	return;
	}

[minwoox]

subscription.request() should be sequentically called

This is for one child stream message.
processor.requestDemand(cumulativeDemand); can be called from multiple child stream messages. Let's say there are two child stream messages and the first one request 10 and the second requests 1, then the condition will be true.

[ikhoon]

Thanks for the explanation. Everything makes sense now.