Provide a way to run service code out of I/O event loops

[kezhenxu94]

Motivations:

When service devs are not very familiar with asynchronous programming, it is very easy to drive Armeria's core event loops into havoc by blocking them.

Framework devs may want to make sure Armeria at least handle I/O and function normally for a certain set of core services, such as PrometheusExpositionService or HealthCheckService, by isolating other non-core services from the I/O event loops.

Modifications:

• Add the serviceWorkerGroup() builder methods to ServerBuilder and AbstractServiceBindingBuilder so a user can specify the service worker groups as shown in the above example.
• Change how Armeria assigns an event loop to a ServiceRequestContext.
  • Modify the constructor of DefaultServiceRequestContext so it accepts an EventLoop.
  • Modify HttpServerHandler.handleRequest(), so it specifies an event loop from the serviceWorkerGroup.

Result:

• Closes #4099.
• Users can add per-service/virtual host/server serviceWorkerGroup property that makes a service use a different EventLoopGroup than ServerBuilder.workerGroup.

[codecov[bot]]

Codecov Report

Patch coverage: 67.61% and project coverage change: +74.21% :tada:

Comparison is base (e344c96) 0.00% compared to head (f8e1c86) 74.21%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #4136       +/-   ##
===========================================
+ Coverage        0   74.21%   +74.21%     
- Complexity      0    19880    +19880     
===========================================
  Files           0     1702     +1702     
  Lines           0    73231    +73231     
  Branches        0     9367     +9367     
===========================================
+ Hits            0    54349    +54349     
- Misses          0    14445    +14445     
- Partials        0     4437     +4437     

Files Changed	Coverage Δ
.../armeria/server/AbstractServiceBindingBuilder.java	63.51% <0.00%> (ø)
...java/com/linecorp/armeria/server/ServerConfig.java	0.00% <ø> (ø)
...linecorp/armeria/server/ServiceBindingBuilder.java	62.68% <0.00%> (ø)
.../linecorp/armeria/server/ServiceConfigSetters.java	100.00% <ø> (ø)
...ver/VirtualHostAnnotatedServiceBindingBuilder.java	38.29% <0.00%> (ø)
...meria/server/VirtualHostServiceBindingBuilder.java	42.62% <0.00%> (ø)
.../linecorp/armeria/server/ServiceConfigBuilder.java	56.52% <33.33%> (ø)
.../server/AbstractAnnotatedServiceConfigSetters.java	71.96% <50.00%> (ø)
...armeria/server/AnnotatedServiceBindingBuilder.java	58.13% <50.00%> (ø)
...ava/com/linecorp/armeria/server/ServerBuilder.java	82.04% <50.00%> (ø)
... and 8 more

... and 1684 files with indirect coverage changes

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[trustin]

@kezhenxu94 Sorry about the conflicts since your last commit here. Please feel free to let us know if you need any help with catching up the recent changes in master. 🙇

[kezhenxu94]

Thanks you @trustin and @ikhoon for your review, I'll take some time to catch up the latest branch and if need help will ask for your help 😇

[kezhenxu94]

Ooops, it's been ~1 month and I haven't found time to pick this up, sorry I have to close this for now and others can continue to work on this 😭

[ikhoon]

Thanks for your initial contribution. 🙇‍♂️ We are happy to take over the remaining work.

[kezhenxu94]

I think I can manage to find some time to continue this work. Just rebase from the master.

[kezhenxu94]

I think all comments are addressed now

[ikhoon]

I think all comments are addressed now

Welcome back! ❤️

[minwoox]

Shouldn't we call httpService.serve(ctx, req) in the serviceWorkerGroup? https://github.com/line/armeria/blob/master/core/src/main/java/com/linecorp/armeria/server/HttpServerHandler.java#L356

[jrhee17]

Added a merge commit due to a conflict with my PR

[github-actions[bot]]

🔍 Build Scan® (commit: f8e1c8644a7da437b4ab5d0007cea1a7ef8f6f94)

Job name	Status	Build Scan®
build-windows-latest-jdk-19	✅	https://ge.armeria.dev/s/3hvt3bhixilsu
build-self-hosted-jdk-8	✅	https://ge.armeria.dev/s/pqg34tq2rh3r4
build-self-hosted-jdk-19-snapshot-blockhound	✅	https://ge.armeria.dev/s/mx5mmugjwfbne
build-self-hosted-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/5ngc75rwtvjpg
build-self-hosted-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/qix6msycvoffg
build-self-hosted-jdk-17-leak	✅	https://ge.armeria.dev/s/rhhiv2wpbso3m
build-self-hosted-jdk-11	✅	https://ge.armeria.dev/s/qsuns47tb4ynq
build-macos-12-jdk-19	✅	https://ge.armeria.dev/s/ccy22lqbv3mda

[jrhee17]

Let me close this PR and create a separate one 🙇