Files

T

History

asmhatreandClaude Sonnet 5.5 db129fb1ce jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

Eight benchmark/demo classes, a deterministic test suite, and 12 captured output files
generated by scripts/run-all.sh on JDK 25.0.5 (Temurin) with JMH 1.37.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b6Fj2JNt7dRev4pZPe

2026-11-08 18:31:11 +00:00

output

jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

2026-11-08 18:31:11 +00:00

scripts

jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

2026-11-08 18:31:11 +00:00

src

jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

2026-11-08 18:31:11 +00:00

pom.xml

jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

2026-11-08 18:31:11 +00:00

README.md

jmh-basics: JMH tutorial module (dead-code elimination, Blackhole, constant folding, warmup/forks, state scopes, -prof gc)

2026-11-08 18:31:11 +00:00

README.md

jmh-basics

Companion code for the ankurm.com post "JMH Tutorial: Writing Java Microbenchmarks That Don't Lie." Module in java-core-examples, the Java-core series. There is deliberately no docs/ folder: the deeper material lives in collapsible sections inside the post itself.

Versions this was built and tested against

Component	Version	Notes
JDK	25.0.5+8 (Temurin, LTS)	Compiler blackholes were auto-detected on this JVM; see `output/02`.
JMH	1.37	Latest GA on Maven Central; released 3 Aug 2023.
JUnit Jupiter	5.11.0
Maven	3.9.11
Host	2 vCPU shared sandbox	Read the shape of the numbers, not the third significant digit.

Quickstart

export JAVA_HOME=/path/to/jdk-25
mvn -q package -DskipTests                       # builds target/benchmarks.jar (shaded, runnable)
java -cp target/classes com.ankurm.jmhbasics.NaiveTimingDemo
java -jar target/benchmarks.jar DeadCodeBenchmark
java -jar target/benchmarks.jar AllocationBenchmark -prof gc

scripts/run-all.sh regenerates every file in output/ (about 8 minutes on 2 vCPUs). scripts/run.sh <ClassName> runs one demo class ad hoc.

What's in here

File	What it shows
`NaiveTimingDemo.java`	The `System.nanoTime()` loop: a discarded result reports 0.000 ns/op, and the kept version changes from round to round while the JIT warms up.
`DeadCodeBenchmark.java`	Empty baseline, discarded result, returned result, `Blackhole`, and constant folding: `Math.pow` of a constant folds, `Math.log` of a constant does not, and a `final` instance field IS folded like a constant (an early draft of the Javadoc claimed the opposite; the measurement and JMHSample_10 both disagreed).
`LifecycleDemo.java`	Counts how often every `@Setup`/`@TearDown` level fires, by running JMH with `forks(0)` in-process.
`ForkingBenchmark.java`	One shared call site, two implementations, run with `-f 0` and `-f 1` to show type-profile pollution.
`StateScopeBenchmark.java`	`Scope.Thread` vs `Scope.Benchmark` with two threads.
`AllocationBenchmark.java`	Escape analysis: the same `new Point(..)` allocates 0 or 24 bytes per call depending on whether it escapes. Use `-prof gc`.
`SumBenchmark.java`	`@Param` over three input sizes, `@Setup` outside the measured region.
`SortBenchmark.java`	Warmup trace (`-wi 10 -w 200ms`) and three benchmark modes in one run.
`JmhBasicsTest.java`	Pins the deterministic claims: lifecycle counts, generated benchmark list, benchmark bodies. No timing assertions.
`output/01-12`	Captured runs of all of the above.

Notes worth knowing before reading the post

Each @BenchmarkMode value is a separate benchmark entry. SortBenchmark.sortCopy carries three modes, so the generated META-INF/BenchmarkList has three lines for it (21 entries for 19 methods; the test pins this).
Run LifecycleDemo from the shaded jar, not from target/classes: JMH is not on the plain classpath.
Timing figures drift. Several error margins in output/ are wide on this shared host. The post draws conclusions only from differences far larger than the error bars.

License

MIT - see the repo-wide LICENSE.