[ISSUE #10467] Reduce per-message allocation in createUniqID and valueOfMagicCode

[wang-jiahua]

Which Issue(s) This PR Fixes

Fixes #10467

Brief Description

Two independent per-message allocation reductions:

1. MessageClientIDSetter.createUniqID(): replaces new char[LEN * 2] per call with a ThreadLocal<char[]> that is allocated once per thread and reused. The char array is only used to build the msgId string within the method and does not escape. JFR shows ~405 char[] allocation events/60s from this site eliminated.

2. MessageVersion.valueOfMagicCode(int): replaces Enum.values() (which copies the backing array per JDK spec) + O(n) loop with direct if-else matching on the two known magic code constants (MESSAGE_MAGIC_CODE and MESSAGE_MAGIC_CODE_V2). Eliminates the per-call array copy on the broker dispatch path.

Compatibility

• createUniqID() produces the same output format — only the internal char buffer allocation strategy changes.
• valueOfMagicCode() behavior is identical for all valid inputs. Invalid magic codes still throw IllegalArgumentException.

How Did You Test This Change

mvn -pl common -Dcheckstyle.skip=false -Dspotbugs.skip=true validate
# 0 Checkstyle violations

mvn -pl common -Dcheckstyle.skip -Dspotbugs.skip=true -Djacoco.skip=true test
# All tests pass

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR optimizes message version resolution and reduces allocations when generating unique message IDs.

Changes:

• Replace enum iteration in MessageVersion#valueOfMagicCode with direct magic-code comparisons for v1/v2.
• Reuse a per-thread char[] buffer in MessageClientIDSetter#createUniqID via ThreadLocal to reduce allocations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
common/src/main/java/org/apache/rocketmq/common/message/MessageVersion.java	Switches magic-code lookup from iterating enum values to direct conditional checks.
common/src/main/java/org/apache/rocketmq/common/message/MessageClientIDSetter.java	Introduces a ThreadLocal<char[]> buffer to reuse memory during unique ID generation.

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[wang-jiahua]

Intentional trade-off. A static lookup map built from values() would achieve the same result but adds complexity for exactly two known constants. The if-else is trivially verifiable and a new version would just add one more line. The values() call this replaces was the problem — it copies the enum backing array on every invocation (JDK spec), which this fix eliminates.

[wang-jiahua]

The retained buffer is LEN * 2 bytes (~32–64 bytes depending on IP version) per thread — negligible even with hundreds of threads. RocketMQ producer threads are long-lived pool threads, so the ThreadLocal lifecycle aligns with thread lifecycle. Added a brief inline comment noting the per-thread retention.

[wang-jiahua]

Good point — renamed sb to buf for clarity.

[oss-sentinel-ai]

Review: Approved ✅

PR: #10469 — Reduce per-message allocation in createUniqID and valueOfMagicCode
Type: Performance (2 files, +12/-10)

Assessment

Optimizes hot path allocations:

• ThreadLocal<char[]> for createUniqID() (eliminates ~405 char[] allocations/60s)
• Direct if-else for valueOfMagicCode() (eliminates Enum.values() array copy)

Verdict

✅ Solid performance optimization based on JFR profiling. Fixes #10467.

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🤖 Automated review by oss-sentinel-ai