Implementation:Apache Flink HybridSource CreateEnumerator

Knowledge Sources	Apache Flink
Domains	Stream_Processing, Source_Architecture
Last Updated	2026-02-09 00:00 GMT

Overview

Concrete tool for creating hybrid source enumerators and readers that wrap source-specific implementations provided by the Apache Flink connector-base module.

Description

HybridSource.createEnumerator creates a HybridSourceSplitEnumerator wrapping the source chain. HybridSource.createReader creates a HybridSourceReader that delegates to source-specific readers. The enumerator uses a SplitEnumeratorContextProxy to translate between HybridSourceSplit and source-specific splits.

Usage

These are internal factory methods called by the Flink runtime when deploying the source.

Code Reference

Source Location

• Repository: Apache Flink
• File: flink-connectors/flink-connector-base/src/main/java/org/apache/flink/connector/base/source/hybrid/HybridSource.java
• Lines: L116-136

Signature

@Internal
@Override
public SourceReader<T, HybridSourceSplit> createReader(SourceReaderContext readerContext)
        throws Exception {
    return new HybridSourceReader<>(readerContext);
}

@Internal
@Override
public SplitEnumerator<HybridSourceSplit, HybridSourceEnumeratorState> createEnumerator(
        SplitEnumeratorContext<HybridSourceSplit> enumContext) {
    return new HybridSourceSplitEnumerator(enumContext, sources, 0, null);
}

@Internal
@Override
public SplitEnumerator<HybridSourceSplit, HybridSourceEnumeratorState> restoreEnumerator(
        SplitEnumeratorContext<HybridSourceSplit> enumContext,
        HybridSourceEnumeratorState checkpoint) throws Exception {
    return new HybridSourceSplitEnumerator(
            enumContext, sources, checkpoint.getCurrentSourceIndex(), checkpoint);
}

Import

import org.apache.flink.connector.base.source.hybrid.HybridSource;
// Internal methods

I/O Contract

Inputs

Name	Type	Required	Description
enumContext	SplitEnumeratorContext<HybridSourceSplit>	Yes	Runtime enumerator context
readerContext	SourceReaderContext	Yes	Runtime reader context

Outputs

Name	Type	Description
enumerator	HybridSourceSplitEnumerator	Wrapping enumerator for the source chain
reader	HybridSourceReader<T>	Wrapping reader for the current source

Usage Examples

Initialization Flow

// Flink runtime calls:
// 1. hybridSource.createEnumerator(context)
//    -> HybridSourceSplitEnumerator(context, sources, startIndex=0, restoredState=null)
//
// 2. hybridSource.createReader(context)
//    -> HybridSourceReader(readerContext) with currentSourceIndex=-1
//
// 3. enumerator.start()
//    -> switchEnumerator() creates source[0]'s enumerator
//    -> sends SwitchSourceEvent to all readers

Related Pages

Implements Principle

• Principle:Apache_Flink_Hybrid_Source_Initialization