Add @SingleThread annotation to dissect processor

[graytaylor0]

Description

Dissect processor is not thread safe. Added "@SingleThread" annotation

Issues Resolved

Resolves #5462

Check List

• New functionality includes testing.
• New functionality has a documentation issue. Please link to it in this PR.
  • New functionality has javadoc added
• Commits are signed with a real name per the DCO

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[dlvenable]

It seems that the main reason this is not thread safe is because the Dissector class mutates its own fields.

data-prepper/data-prepper-plugins/dissect-processor/src/main/java/org/opensearch/dataprepper/plugins/processor/dissect/Dissector.java

Lines 26 to 32 in fee636c

	private Map<String, SkipField> skipFieldMap;
	private Map<String, NormalField> normalFieldMap;
	private Map<String, IndirectField> indirectFieldMap;
	private Map<String, List<AppendField>> unAppendedFieldsMap;
	private final FieldHelper fieldHelper = new FieldHelper();
	private final LinkedList<Field> fieldsList = new LinkedList<>();
	private final LinkedList<Delimiter> delimiterList = new LinkedList<>();

Might there be other bugs with this behavior?

[graytaylor0]

It seems that the main reason this is not thread safe is because the Dissector class mutates its own fields.

data-prepper/data-prepper-plugins/dissect-processor/src/main/java/org/opensearch/dataprepper/plugins/processor/dissect/Dissector.java

Lines 26 to 32 in fee636c

	private Map<String, SkipField> skipFieldMap;
	private Map<String, NormalField> normalFieldMap;
	private Map<String, IndirectField> indirectFieldMap;
	private Map<String, List<AppendField>> unAppendedFieldsMap;
	private final FieldHelper fieldHelper = new FieldHelper();
	private final LinkedList<Field> fieldsList = new LinkedList<>();
	private final LinkedList<Delimiter> delimiterList = new LinkedList<>();

Might there be other bugs with this behavior?

I'm not sure. There could be, but so far this processor works fine with a single thread. Don't you think this is a good short term fix though? Seems like the refactor to avoid this mutation may be larger

[dlvenable]

It seems that the main reason this is not thread safe is because the Dissector class mutates its own fields.

data-prepper/data-prepper-plugins/dissect-processor/src/main/java/org/opensearch/dataprepper/plugins/processor/dissect/Dissector.java

Lines 26 to 32 in fee636c

	private Map<String, SkipField> skipFieldMap;
	private Map<String, NormalField> normalFieldMap;
	private Map<String, IndirectField> indirectFieldMap;
	private Map<String, List<AppendField>> unAppendedFieldsMap;
	private final FieldHelper fieldHelper = new FieldHelper();
	private final LinkedList<Field> fieldsList = new LinkedList<>();
	private final LinkedList<Delimiter> delimiterList = new LinkedList<>();

Might there be other bugs with this behavior?

I'm not sure. There could be, but so far this processor works fine with a single thread. Don't you think this is a good short term fix though? Seems like the refactor to avoid this mutation may be larger

Yea, that may be a lot.

[oeyh]

@graytaylor0 Good find! I remember seeing a customer issue where dissect processor returns weird results a few times out of like a million processed events. This might have been the root cause.