org.apache.flink.connector.base.source.reader

Class SourceReaderBase<E,T,SplitT extends SourceSplit,SplitStateT>

java.lang.Object

org.apache.flink.connector.base.source.reader.SourceReaderBase<E,T,SplitT,SplitStateT>

Type Parameters:

E - The rich element type that contains information for split state update or timestamp extraction.

T - The final element type to emit.

SplitT - the immutable split type.

SplitStateT - the mutable type of split state.

All Implemented Interfaces:

AutoCloseable, CheckpointListener, SourceReader<T,SplitT>

Direct Known Subclasses:

PulsarOrderedSourceReader, PulsarUnorderedSourceReader, SingleThreadMultiplexSourceReaderBase

@PublicEvolving
public abstract class SourceReaderBase<E,T,SplitT extends SourceSplit,SplitStateT>
extends Object
implements SourceReader<T,SplitT>

An abstract implementation of SourceReader which provides some synchronization between the mail box main thread and the SourceReader internal threads. This class allows user to just provide a SplitReader and snapshot the split state.

This implementation provides the following metrics out of the box:

• OperatorIOMetricGroup.getNumRecordsInCounter()

Field Summary

Fields

Modifier and Type	Field and Description
protected Configuration	config The raw configurations that may be used by subclasses.
protected SourceReaderContext	context The context of this source reader.
protected SourceReaderOptions	options The configuration for the reader.
protected RecordEmitter<E,T,SplitStateT>	recordEmitter The record emitter to handle the records read by the SplitReaders.
protected SplitFetcherManager<E,SplitT>	splitFetcherManager The split fetcher manager to run split fetchers.

Constructor Summary

Constructors

Constructor and Description
SourceReaderBase(FutureCompletingBlockingQueue<RecordsWithSplitIds<E>> elementsQueue, SplitFetcherManager<E,SplitT> splitFetcherManager, RecordEmitter<E,T,SplitStateT> recordEmitter, Configuration config, SourceReaderContext context)

Method Summary

Modifier and Type	Method and Description
void	addSplits(List<SplitT> splits) Adds a list of splits for this reader to read.
void	close()
int	getNumberOfCurrentlyAssignedSplits() Gets the number of splits the reads has currently assigned.
void	handleSourceEvents(SourceEvent sourceEvent) Handle a custom source event sent by the SplitEnumerator.
protected abstract SplitStateT	initializedState(SplitT split) When new splits are added to the reader.
CompletableFuture<Void>	isAvailable() Returns a future that signals that data is available from the reader.
void	notifyNoMoreSplits() This method is called when the reader is notified that it will not receive any further splits.
protected abstract void	onSplitFinished(Map<String,SplitStateT> finishedSplitIds) Handles the finished splits to clean the state if needed.
InputStatus	pollNext(ReaderOutput<T> output) Poll the next available record into the SourceOutput.
List<SplitT>	snapshotState(long checkpointId) Checkpoint on the state of the source.
void	start() Start the reader.
protected abstract SplitT	toSplitType(String splitId, SplitStateT splitState) Convert a mutable SplitStateT to immutable SplitT.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.flink.api.connector.source.SourceReader

notifyCheckpointComplete

Methods inherited from interface org.apache.flink.api.common.state.CheckpointListener

notifyCheckpointAborted

Field Detail

recordEmitter

protected final RecordEmitter<E,T,SplitStateT> recordEmitter

The record emitter to handle the records read by the SplitReaders.

splitFetcherManager

protected final SplitFetcherManager<E,SplitT extends SourceSplit> splitFetcherManager

The split fetcher manager to run split fetchers.

options

protected final SourceReaderOptions options

The configuration for the reader.

config

protected final Configuration config

The raw configurations that may be used by subclasses.

context

protected SourceReaderContext context

The context of this source reader.

Constructor Detail

SourceReaderBase

public SourceReaderBase(FutureCompletingBlockingQueue<RecordsWithSplitIds<E>> elementsQueue,
                        SplitFetcherManager<E,SplitT> splitFetcherManager,
                        RecordEmitter<E,T,SplitStateT> recordEmitter,
                        Configuration config,
                        SourceReaderContext context)

Method Detail

start

public void start()

Description copied from interface: SourceReader

Start the reader.

Specified by:

start in interface SourceReader<T,SplitT extends SourceSplit>

pollNext

public InputStatus pollNext(ReaderOutput<T> output)
                     throws Exception

Description copied from interface: SourceReader

Poll the next available record into the SourceOutput.

The implementation must make sure this method is non-blocking.

Although the implementation can emit multiple records into the given SourceOutput, it is recommended not doing so. Instead, emit one record into the SourceOutput and return a InputStatus.MORE_AVAILABLE to let the caller thread know there are more records available.

Specified by:

pollNext in interface SourceReader<T,SplitT extends SourceSplit>

Returns:

The InputStatus of the SourceReader after the method invocation.

Throws:

Exception

isAvailable

public CompletableFuture<Void> isAvailable()

Description copied from interface: SourceReader

Returns a future that signals that data is available from the reader.

Once the future completes, the runtime will keep calling the SourceReader.pollNext(ReaderOutput) method until that methods returns a status other than InputStatus.MORE_AVAILABLE. After that the, the runtime will again call this method to obtain the next future. Once that completes, it will again call SourceReader.pollNext(ReaderOutput) and so on.

The contract is the following: If the reader has data available, then all futures previously returned by this method must eventually complete. Otherwise the source might stall indefinitely.

It is not a problem to have occasional "false positives", meaning to complete a future even if no data is available. However, one should not use an "always complete" future in cases no data is available, because that will result in busy waiting loops calling pollNext(...) even though no data is available.

Specified by:

isAvailable in interface SourceReader<T,SplitT extends SourceSplit>

Returns:

a future that will be completed once there is a record available to poll.

snapshotState

public List<SplitT> snapshotState(long checkpointId)

Description copied from interface: SourceReader

Checkpoint on the state of the source.

Specified by:

snapshotState in interface SourceReader<T,SplitT extends SourceSplit>

Returns:

the state of the source.

addSplits

public void addSplits(List<SplitT> splits)

Description copied from interface: SourceReader

Adds a list of splits for this reader to read. This method is called when the enumerator assigns a split via SplitEnumeratorContext.assignSplit(SourceSplit, int) or SplitEnumeratorContext.assignSplits(SplitsAssignment).

Specified by:

addSplits in interface SourceReader<T,SplitT extends SourceSplit>

Parameters:

splits - The splits assigned by the split enumerator.

notifyNoMoreSplits

public void notifyNoMoreSplits()

Description copied from interface: SourceReader

This method is called when the reader is notified that it will not receive any further splits.

It is triggered when the enumerator calls SplitEnumeratorContext.signalNoMoreSplits(int) with the reader's parallel subtask.

Specified by:

notifyNoMoreSplits in interface SourceReader<T,SplitT extends SourceSplit>

handleSourceEvents

public void handleSourceEvents(SourceEvent sourceEvent)

Description copied from interface: SourceReader

Handle a custom source event sent by the SplitEnumerator. This method is called when the enumerator sends an event via SplitEnumeratorContext.sendEventToSourceReader(int, SourceEvent).

This method has a default implementation that does nothing, because most sources do not require any custom events.

Specified by:

handleSourceEvents in interface SourceReader<T,SplitT extends SourceSplit>

Parameters:

sourceEvent - the event sent by the SplitEnumerator.

close

public void close()
           throws Exception

Specified by:

close in interface AutoCloseable

Throws:

Exception

getNumberOfCurrentlyAssignedSplits

public int getNumberOfCurrentlyAssignedSplits()

Gets the number of splits the reads has currently assigned.

These are the splits that have been added via addSplits(List) and have not yet been finished by returning them from the SplitReader.fetch() as part of RecordsWithSplitIds.finishedSplits().

onSplitFinished

protected abstract void onSplitFinished(Map<String,SplitStateT> finishedSplitIds)

Handles the finished splits to clean the state if needed.

initializedState

protected abstract SplitStateT initializedState(SplitT split)

When new splits are added to the reader. The initialize the state of the new splits.

Parameters:

split - a newly added split.

toSplitType

protected abstract SplitT toSplitType(String splitId,
                                      SplitStateT splitState)

Convert a mutable SplitStateT to immutable SplitT.

Parameters:

splitState - splitState.

Returns:

an immutable Split state.