Prior to this commit, the Spring Framework test suite would rely only on
"Performance" tests associated with a specific CI build. As outlined in
gh-24830, the way they're built and executed is not working well
anymore.
This commit introduces a new JMH benchmark infrastructure in the build.
The goal here is not to run those benchmarks as part of a CI build, but
rather provide a proper infrastructure for writing and locally running
micro-benchmarks when working on specific optimizations.
This commit adds and configures a Gradle JMH plugin to allow for JMH
benchmark classes in Spring Framework modules (in `src/jmh/java` of each
`spring-*` module). It's also relaxing the checkstyle rules for JMH
classes, especially around Javadoc rules: this code is not meant to
have Javadocs.
Finally, this commit links to a new Wiki page on the project GitHub
repository documenting the infrastructure and helping contributors to
run and design benchmarks.
See gh-24830