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https://issues.apache.org/jira/browse/SPARK-59382?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated SPARK-59382:
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Labels: pull-request-available (was: )
> Avoid redundant volatile reads of lazy caches in UTF8String
> -----------------------------------------------------------
>
> Key: SPARK-59382
> URL: https://issues.apache.org/jira/browse/SPARK-59382
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 4.1.0
> Reporter: David Mollitor
> Priority: Trivial
> Labels: pull-request-available
>
> h2. Summary
> {{UTF8String}} lazily computes and caches several values in {{volatile}}
> fields: {{numChars}}, {{isFullAscii}}, {{isValid}}, and {{numBytesValid}}.
> The accessor methods read the {{volatile}} field two (or three) times per
> call -- the "is it computed yet" check plus the return -- and two callers
> invoke {{numChars()}} twice. A {{volatile}} read cannot be kept in a register
> or hoisted by the JIT, and on AArch64 it compiles to a load-acquire
> ({{ldar}}) rather than a plain load. This reads each field once into a local,
> halving the volatile reads on the warm path.
> This is a small, behavior-preserving micro-optimization; no functional change.
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