Ankur Mhatre
eaa8171966
Three replicas of one application against one PostgreSQL database, proving duplicate @Scheduled execution and then removing it with ShedLock: 24 executions where 8 were due, then 7 for 7 ticks. Also measured: @SchedulerLock without @EnableSchedulerLock does nothing and warns about nothing; spring.task.scheduling.pool.size=1 does not starve a fixedRate job but delays it and fires 35 of 40 executions in a burst; and a node whose clock is 40 seconds fast takes a live lock unless the provider uses usingDbTime().
37 lines
2.3 KiB
Markdown
37 lines
2.3 KiB
Markdown
# spring-async-demo
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Companion code for the asynchronous execution and scheduling series on
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[ankurm.com](https://ankurm.com). Each
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directory is a self-contained Maven project for one article, with its own `pom.xml`, its own
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numbered documentation chapters, and its own captured output under `docs/output/` — regenerated
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by that module's `scripts/run-all.sh`, never typed by hand.
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| Module | Article | What it demonstrates |
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|---|---|---|
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| [`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 |
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| [`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 |
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## Common ground
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All modules target the same verified stack: **JDK 25** (Temurin 25.0.4.1+1), **Spring Boot
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4.1.1**, **Spring Framework 7.0.9**. Versions were read from `maven-metadata.xml` on Maven Central
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and from Boot's own `spring-boot-dependencies` POM, rather than from release announcements.
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Everything is asserted by a test and captured to a file. The measurement is nearly always the same
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one: the name of the thread that ran the work, returned by the code itself. Timing cannot tell a
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fast synchronous call from an asynchronous one, which is why `@Async` failures survive so long in
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production.
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The two modules share a mechanism, which is why they live together: both `@Async` and ShedLock's
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default `PROXY_METHOD` intercept mode are Spring AOP proxies. Every proxy limitation the `async`
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module measures — self-invocation, `final` methods — applies unchanged to a
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`@SchedulerLock` method, and silently produces an unlocked job rather than a synchronous one.
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The `scheduling` module also needs a database. `scheduling/scripts/postgres.sh` unpacks a
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throwaway PostgreSQL 14 into `target/` with no Docker and no root, which is how its transcripts
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were produced; `docker-compose.yml` is there for anyone who would rather use Docker.
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## Licence
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MIT — see [LICENSE](LICENSE).
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