Fix data race in JsonPayloadSerializerProvider.

[stankiewicz]

The anonymous class returned by getSerializer captured ObjectMapper instances. When these were serialized (e.g., during pipeline translation in DirectRunner), a data race occurred in Jackson's DeserializerCache.writeReplace() due to concurrent modification of internal caches during serialization.

This change introduces a concrete JsonPayloadSerializer class that marks the ObjectMapper instances as transient and initializes them lazily. This avoids serializing the mappers and eliminates the data race.

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical data race that arose from the serialization of ObjectMapper instances within anonymous classes. By refactoring the serialization logic into a dedicated class and ensuring that ObjectMapper instances are not serialized but rather lazily initialized, the change enhances the robustness and thread safety of JSON payload processing.

Highlights

• Data Race Fix: Addressed a data race occurring in Jackson's DeserializerCache.writeReplace() when ObjectMapper instances, captured by anonymous classes, were serialized during pipeline translation.
• New PayloadSerializer Implementation: Introduced a concrete JsonPayloadSerializer class to encapsulate the serialization and deserialization logic for JSON payloads.
• Transient and Lazy Initialization: Marked ObjectMapper instances within the new JsonPayloadSerializer as transient and implemented lazy, synchronized initialization to prevent their serialization and resolve the data race.

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[github-actions]

Checks are failing. Will not request review until checks are succeeding. If you'd like to override that behavior, comment assign set of reviewers

[stankiewicz]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors JsonPayloadSerializerProvider to use a private inner class, JsonPayloadSerializer, for handling serialization and deserialization with lazy-loaded ObjectMapper instances. The review feedback suggests several improvements for concurrency and code cleanliness: marking the mapper fields as volatile to ensure visibility, implementing double-checked locking to reduce synchronization overhead in high-throughput scenarios, and removing redundant null initializations in the constructor.

[gemini-code-assist]

The ObjectMapper fields should be marked as volatile to ensure proper visibility when using lazy initialization, especially if using double-checked locking to avoid synchronization overhead.

Suggested change

	private transient @Nullable ObjectMapper deserializeMapper;
	private transient @Nullable ObjectMapper serializeMapper;
	private transient volatile @Nullable ObjectMapper deserializeMapper;
	private transient volatile @Nullable ObjectMapper serializeMapper;

[gemini-code-assist]

Explicitly initializing fields to null in the constructor is redundant in Java, as they are already initialized to their default values. This can be simplified.

    public JsonPayloadSerializer(Schema schema) {
      this.schema = schema;
    }

[gemini-code-assist]

Using synchronized on the entire method for every access to the ObjectMapper can introduce contention in high-throughput scenarios, as these methods are called for every record processed. Consider using double-checked locking (with the fields marked as volatile) to optimize the common path where the mappers are already initialized.

    private ObjectMapper getDeserializeMapper() {
      ObjectMapper result = deserializeMapper;
      if (result == null) {
        synchronized (this) {
          result = deserializeMapper;
          if (result == null) {
            deserializeMapper = result = RowJsonUtils.newObjectMapperWith(RowJsonDeserializer.forSchema(schema));
          }
        }
      }
      return result;
    }

    private ObjectMapper getSerializeMapper() {
      ObjectMapper result = serializeMapper;
      if (result == null) {
        synchronized (this) {
          result = serializeMapper;
          if (result == null) {
            serializeMapper = result = RowJsonUtils.newObjectMapperWith(RowJsonSerializer.forSchema(schema));
          }
        }
      }
      return result;
    }

[github-actions]

Assigning reviewers:

R: @chamikaramj for label java.

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