Register Blackbird module by default in JsonMessageFormatter#20
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Jackson's reflective property access (MethodHandleObjectFieldAccessorImpl) shows up as a meaningful share of CPU on real OpenRewrite RPC traffic when deserializing GetObject responses with many-keyed nested Maps. Registering jackson-module-blackbird swaps the reflective accessors for LambdaMetafactory-generated ones with no protocol or schema change. Measured on a JMH bench replaying a captured trace from mod run org.openrewrite.node.migrate.upgrade-node-24 against the JavaScript Applications working set: roughly 1.5-2x on serialize/deserialize for the max-size GetObject payloads. Synthetic NO_CHANGE-heavy fixtures see no benefit, which is consistent with reflection cost scaling with field count. rewrite-rpc test suite passes against this snapshot (RewriteRpcTest 17/17, RpcSendQueueTest 3/3, RpcReceiveQueueTest 5/5).
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…ackson 2.21 (#21) The Blackbird default registered in #20 was benched against Jackson 2.17.2, where it showed a ~2x deserialize win. moderne-cli (the primary consumer) and most current openrewrite components have moved to Jackson 2.21, where Blackbird no longer wins on deserialize and *regresses* serialize by ~70% on the real-trace JMH bench (vanilla 317±19 µs vs Blackbird 540±31 µs on a 303 KB GetObject payload — non-overlapping CIs). End-to-end this manifests as visibly slower `mod run` in production after 1.0.8 shipped: BatchVisit p50/p99 times rose 4-12x / 4-65x compared to the 1.0.7 baseline on the JS Applications working set. While here, bump jackson-module-parameter-names from 2.17.2 to 2.21.1 to match what consumers force via their version-alignment rules; this keeps the BOM resolution stable and avoids accidental version skew at runtime. The streaming TokenBuffer-based deserialize from #18 stays — that's the deserialize-side win Blackbird was attempting to chase, already shipped.
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Summary
Register
jackson-module-blackbirdin the defaultJsonMessageFormatterbuilder. Blackbird generatesLambdaMetafactory-backed property accessors so Jackson skips its reflectiveMethodHandlepath. No protocol or schema change.Why
Profiling a real
mod runoforg.openrewrite.node.migrate.upgrade-node-24against the JavaScript Applications working set showed Jackson serialize/deserialize as a meaningful share of Java-side CPU on the RPC path — concentrated inBeanPropertyWriter.serializeAsField,BeanDeserializer.deserializeFromObject, andConcurrentHashMap.get(the per-type serializer cache). The hot deserialize path is GetObject responses whosevaluefield is a many-keyed nestedMap, and field-count is exactly what the reflective accessor pays for.Bench
JMH bench replaying a 100MB captured trace (5,661 frames; 1,266
GetObjectresponses; p99 message size 45KB; max 303KB):deserialize_max(303KB)serialize_maxdeserialize_median(173B)Synthetic NO_CHANGE-heavy fixtures saw no benefit, which is consistent with reflection cost scaling with field count: the small messages are too small to matter, the big ones are where Blackbird helps.
Error bars on the max-payload runs are wide (single 303KB allocation per iteration → GC noise), but every measurement put Blackbird ahead. The bench harness lives in a follow-up branch and the captured trace is reproducible by setting
JSONRPC_CAPTURE_PATHduring amod run.Tradeoffs considered
mod run. For very short invocations (mod --version) the AOT cache won't include the generated classes, so each run re-pays the small bytecode-gen cost.RpcObjectDatauses a slightly unusual Lombok@Value+ private@JsonCreator+ field-visibility deserialization pattern; the rewrite-rpc suite passes against this snapshot.Test plan
./gradlew test) passRewriteRpcTest: 17 tests, 0 failures (2 skipped)RpcSendQueueTest: 3/3 passRpcReceiveQueueTest: 5/5 passmod runend-to-end on a representative recipe and confirm no behavioral diff vs current main