HADOOP-19900. EC write can fail with ArrayIndexOutOfBoundsException due to CoderUtil emptyChunk resize race

[smengcl]

https://issues.apache.org/jira/browse/HADOOP-19900

Contains content generated by Claude Code (Opus 4.7)

Description of PR

Fix a race in CoderUtil.getEmptyChunk() that can cause EC writes to fail with ArrayIndexOutOfBoundsException during parity encoding.

This can be hit when multiple EC key output streams in the same client JVM use the Java raw EC encoder concurrently with different encode/reset lengths. Each ECKeyOutputStream has its own encoder, but all Java encoders share the static CoderUtil.emptyChunk cache. If native ISA-L is unavailable or not selected, the Java RSRawEncoder clears parity output buffers through CoderUtil.resetOutputBuffers(). Under concurrent close/flush paths, especially with partial final stripes of different sizes, one stream can grow the shared zero buffer for a larger encode while another smaller encode races and shrinks it, causing the larger encode’s later System.arraycopy() to throw ArrayIndexOutOfBoundsException.

For more details, see apache/ozone#10324

How was this patch tested?

• Added Claude-generated repro test.

For code changes:

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[ZanderXu]

Nice catch.

LGTM +1

[smengcl]

Thanks @ZanderXu for reviewing this!

Merging this as yetus looks good.