Removing thread contention from Unsynchronized Map Benchmarks#11679
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dougqh wants to merge 7 commits into
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Removing thread contention from Unsynchronized Map Benchmarks#11679dougqh wants to merge 7 commits into
dougqh wants to merge 7 commits into
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Throughput microbenchmark for TagMap insert/getObject/getEntry over a representative HTTP-server tag set. All mutable state (the read map) lives in @State(Scope.Thread) so @threads(8) runs measure TagMap rather than cross-thread contention on a shared map/counter/flyweight — the flaw that made earlier TagMap benchmarks misleading. Run config is baked into annotations (the me.champeau.jmh plugin ignores -Pjmh.* flags). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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🟢 Java Benchmark SLOs — All performance SLOs passed
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Commit: Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion. |
dougqh
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Jun 22, 2026
| public class TagMapAccessBenchmark { | ||
| // a representative HTTP-server-ish tag set (immutable -> safe to share across threads) | ||
| static final String[] NAMES = { | ||
| "http.request.method", |
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Future intended changes will care about the specifics of the tags, so using real tags is preferable for future-proofing
sharedLookupIndex was a plain static int incremented by all 8 JMH threads without synchronization — a data race that turned the get benchmarks into a contention measurement rather than a map measurement. Move the index to @State(Scope.Thread) so each thread has its own cursor, matching the approach used in TagMapAccessBenchmark. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Without this, -Pjmh.includes is silently ignored by the me.champeau.jmh plugin, requiring a full fat-jar build to run a single benchmark. -PtestJvm was also ignored for JMH execution, defaulting to the Gradle daemon JVM regardless of the requested version. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Re-run after fixing the shared-index data race, on Java 17 with correct per-thread scaffolding state. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The '2x faster construction' claim was stale — Java 17 numbers show ~40%. Also clarifies that LinkedHashMap's cost is purely at construction; gets and iteration are equivalent to HashMap. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…sBenchmark Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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What This Does
Adds a throughput microbenchmark for the core
TagMapaccess paths —insert,getObject(raw value),getEntry— over a representative HTTP-server-ish tag set.Motivation
Before making further changes to TagMap, I want a more robust benchmark in place. The shared counter used in the benchmark previously was masking some of the differences as compared to other Maps.
Additional Notes
Runs at
@Threads(8). All shared state is immutable (NAMES/VALUES); every bit of mutable state (the pre-populated read map) lives in a@State(Scope.Thread)holder, so threads never contend on a shared map, index, or reader flyweight. Earlier TagMap benchmarks shared a cross-thread counter/index, which turned the result into a contention measurement rather than a TagMap measurement — this layout avoids that. Indices are plain per-invocation locals.Run config is baked into annotations (
@Fork/@Warmup/@Measurement/@Threads) rather than relying on-Pjmh.*flags, which theme.champeau.jmhplugin ignores.Notes
LegacyTagMapremoval (Remove LegacyTagMap; OptimizedTagMap is the sole TagMap implementation #11678) — uses only the publicTagMapAPI, so it builds/runs on master and on that branch alike.DDSpanbenchmark follows once its tracer setup is quieted (a no-op writer to stop per-op DEBUG logging from contaminating throughput).🤖 Generated with Claude Code