# spring-async-demo

Companion code for the asynchronous execution and scheduling series on
[ankurm.com](https://ankurm.com). Each
directory is a self-contained Maven project for one article, with its own `pom.xml`, its own
numbered documentation chapters, and its own captured output under `docs/output/` — regenerated
by that module's `scripts/run-all.sh`, never typed by hand.

| Module | Article | What it demonstrates |
|---|---|---|
| [`async/`](async/README.md) | [@Async in Spring Boot 4: Executors, Virtual Threads and the Self-Invocation Trap](https://ankurm.com/spring-boot-4-async-executors-virtual-threads/) | Which thread a method actually ran on, in every case where the answer is not the one you expect |
| [`scheduling/`](scheduling/README.md) | [@Scheduled, ShedLock and Distributed Cron: Scheduling That Survives Three Replicas](https://ankurm.com/spring-scheduled-shedlock-distributed-cron/) | Three replicas against one database running the same job three times, then one row and one conditional UPDATE fixing it |
| [`virtual-threads-benchmark/`](virtual-threads-benchmark/README.md) | [Virtual Threads on Spring Boot 4.1: The Benchmarks, Re-Run, and the Pinning Advice That Expired](https://ankurm.com/leveraging-virtual-threads-in-spring-boot-3-4-building-high-throughput-services/) | Platform threads vs virtual threads, re-benchmarked on Boot 4.1.1 / JDK 25, plus JEP 491's fix to `synchronized` pinning proven against a real JDK |
| [`virtual-threads-benchmark-webflux/`](virtual-threads-benchmark-webflux/README.md) | [Virtual Threads vs Reactive (WebFlux) vs Platform Threads: Benchmarks and a Decision Framework](https://ankurm.com/virtual-threads-vs-webflux-vs-platform-threads-spring-boot-benchmarks/) | The WebFlux leg of the three-way comparison, plus the event-loop-starvation failure mode an isolated CPU benchmark can't show |

## Common ground

All modules target the same verified stack: **JDK 25** (Temurin 25.0.4.1+1), **Spring Boot
4.1.1**, **Spring Framework 7.0.9**. Versions were read from `maven-metadata.xml` on Maven Central
and from Boot's own `spring-boot-dependencies` POM, rather than from release announcements.

Everything is asserted by a test and captured to a file. The measurement is nearly always the same
one: the name of the thread that ran the work, returned by the code itself. Timing cannot tell a
fast synchronous call from an asynchronous one, which is why `@Async` failures survive so long in
production.

The two modules share a mechanism, which is why they live together: both `@Async` and ShedLock's
default `PROXY_METHOD` intercept mode are Spring AOP proxies. Every proxy limitation the `async`
module measures — self-invocation, `final` methods — applies unchanged to a
`@SchedulerLock` method, and silently produces an unlocked job rather than a synchronous one.

The `scheduling` module also needs a database. `scheduling/scripts/postgres.sh` unpacks a
throwaway PostgreSQL 14 into `target/` with no Docker and no root, which is how its transcripts
were produced; `docker-compose.yml` is there for anyone who would rather use Docker.

`virtual-threads-benchmark` and `virtual-threads-benchmark-webflux` are a similar pair: the
first re-benchmarks platform threads against virtual threads for one post, the second adds the
WebFlux leg for a different, three-way-comparison post, and reuses the first module's
committed transcripts rather than re-measuring the same thing twice. Both use the same
client-side load generator (`java.net.http.HttpClient` on a virtual-thread executor, client
role only) so all three threading models in the three-way post are measured the same way.

## Licence

MIT — see [LICENSE](LICENSE).