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https://issues.apache.org/jira/browse/FLINK-39291?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated FLINK-39291:
-----------------------------------
Labels: pull-request-available (was: )
> FlinkScalaKryoInstantiator uses StdInstantiatorStrategy directly, bypassing
> constructors and causing NPE for classes requiring initialization
> ---------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: FLINK-39291
> URL: https://issues.apache.org/jira/browse/FLINK-39291
> Project: Flink
> Issue Type: Improvement
> Components: API / Type Serialization System
> Reporter: Liu
> Priority: Major
> Labels: pull-request-available
>
> h1. Problem
> FlinkScalaKryoInstantiator.newKryo() sets the InstantiatorStrategy to
> StdInstantiatorStrategy directly, which uses Objenesis to create instances
> without invoking any constructor. This is inconsistent with
> KryoSerializer.getKryoInstance()'s fallback path, which uses
> DefaultInstantiatorStrategy with StdInstantiatorStrategy as a fallback —
> meaning it first attempts to invoke the no-arg constructor and only falls
> back to Objenesis if that fails.
> When flink-table-api-scala is on the classpath (e.g., added to the Flink lib
> directory), KryoSerializer will load FlinkScalaKryoInstantiator and use the
> Kryo instance it creates. Any class that relies on its no-arg constructor to
> initialize internal state will then fail during deserialization, because the
> constructor is never invoked.
> h1. Reproduction
> A concrete example is Apache Iceberg's SerializableByteBufferMap, which
> initializes its wrapped field (Map<Integer, ByteBuffer>) in the no-arg
> constructor. When deserialized via Kryo's MapSerializer,
> MapSerializer.create() calls kryo.newInstance(), which (under
> StdInstantiatorStrategy) bypasses the constructor, leaving wrapped = null.
> Subsequently, MapSerializer.read() calls map.put(key, value), which delegates
> to wrapped.put() — resulting in a NullPointerException.
> h1. Root Cause
> In FlinkScalaKryoInstantiator.scala (line 63):
> k.setInstantiatorStrategy(new org.objenesis.strategy.StdInstantiatorStrategy)
> This was inherited from the original Twitter Chill code and preserved during
> the Kryo 5 upgrade (FLINK-3154).
> h1. Fix
> Align FlinkScalaKryoInstantiator with KryoSerializer's default strategy:
> {code:java}
> val initStrategy = new
> com.esotericsoftware.kryo.util.DefaultInstantiatorStrategy()
> initStrategy.setFallbackInstantiatorStrategy(new
> org.objenesis.strategy.StdInstantiatorStrategy)
> k.setInstantiatorStrategy(initStrategy) {code}
> This change:
> * First attempts to use the no-arg constructor (via
> DefaultInstantiatorStrategy)
> * Falls back to Objenesis only if no constructor is available
> * Is backward-compatible: all Scala types with registered custom serializers
> are unaffected
> * Eliminates the behavioral inconsistency between the two Kryo
> initialization code paths in KryoSerializer
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