LuciferYang opened a new pull request, #3447:
URL: https://github.com/apache/parquet-java/pull/3447
### Rationale for this change
Fixes #3398
In `FromCharSequenceBinary`, a `ThreadLocal<CharsetEncoder>` is initialized
via `ThreadLocal.withInitial(StandardCharsets.UTF_8::newEncoder)`. The lambda
generates a dynamic `Supplier` class loaded by the current application
ClassLoader. In long-lived thread pool environments (Spark/Flink executors, web
containers), pooled worker threads survive job cancellation or
hot-redeployment, retaining a strong reference chain: `Thread` →
`ThreadLocalMap` → `SuppliedThreadLocal` → lambda → ClassLoader. This
permanently pins the application ClassLoader, preventing class unloading and
causing linear Metaspace growth, eventually leading to
`java.lang.OutOfMemoryError: Metaspace`.
### What changes are included in this PR?
Replaced the `ThreadLocal<CharsetEncoder>` based encoding in
`FromCharSequenceBinary` with a stateless
`value.toString().getBytes(StandardCharsets.UTF_8)`, consistent with the
existing `FromStringBinary.encodeUTF8()` at line 251 in the same file.
Also note that the original `catch (CharacterCodingException)` block was
effectively dead code — `StandardCharsets.UTF_8` is a standard charset
guaranteed to be available, so `CharsetEncoder.encode()` would never throw
`CharacterCodingException` for unsupported charset reasons.
### Are these changes tested?
Yes. All existing tests in `parquet-column` pass without modification.
### Are there any user-facing changes?
No. The encoding behavior is identical — both approaches produce the same
UTF-8 byte sequence.
**Performance note**: `fromCharSequence()` is only invoked as a fallback in
`AvroWriteSupport.fromAvroString()` for non-String, non-Utf8 `CharSequence`
implementations. The dominant write paths use `fromReusedByteArray()` (Avro
`Utf8`) and `fromString()` (Java `String`), both of which already use stateless
encoding without `ThreadLocal`. Therefore, no measurable performance regression
is expected.
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