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().
2.3 KiB
spring-async-demo
Companion code for the asynchronous execution and scheduling series on
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 in Spring Boot 4: Executors, Virtual Threads and the Self-Invocation Trap | Which thread a method actually ran on, in every case where the answer is not the one you expect |
scheduling/ |
@Scheduled, ShedLock and Distributed Cron: Scheduling That Survives Three Replicas | Three replicas against one database running the same job three times, then one row and one conditional UPDATE fixing it |
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.
Licence
MIT — see LICENSE.