org.apache.flink.api.connector.source.lib.util

Class IteratorSourceReaderBase<E,O,IterT extends Iterator<E>,SplitT extends IteratorSourceSplit<E,IterT>>

java.lang.Object

org.apache.flink.api.connector.source.lib.util.IteratorSourceReaderBase<E,O,IterT,SplitT>

Type Parameters:

E - The type of events returned by the reader.

IterT - The type of the iterator that produces the events. This type exists to make the conversion between iterator and IteratorSourceSplit type safe.

SplitT - The concrete type of the IteratorSourceSplit that creates and converts the iterator that produces this reader's elements.

All Implemented Interfaces:

AutoCloseable, CheckpointListener, SourceReader<O,SplitT>

Direct Known Subclasses:

GeneratingIteratorSourceReader, IteratorSourceReader

@Public
public abstract class IteratorSourceReaderBase<E,O,IterT extends Iterator<E>,SplitT extends IteratorSourceSplit<E,IterT>>
extends Object
implements SourceReader<O,SplitT>

A SourceReader that returns the values of an iterator, supplied via an IteratorSourceSplit.

The IteratorSourceSplit is also responsible for taking the current iterator and turning it back into a split for checkpointing.

Constructor Summary

Constructors

Constructor and Description
IteratorSourceReaderBase(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()
protected abstract O	convert(E value)
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.
InputStatus	pollNext(ReaderOutput<O> output) Poll the next available record into the ReaderOutput.
List<SplitT>	snapshotState(long checkpointId) Checkpoint on the state of the source.
void	start() Start the reader.
protected void	start(SourceReaderContext context)

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

handleSourceEvents, notifyCheckpointComplete, pauseOrResumeSplits

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

notifyCheckpointAborted

Constructor Detail

IteratorSourceReaderBase

public IteratorSourceReaderBase(SourceReaderContext context)

Method Detail

start

public void start()

Description copied from interface: SourceReader

Start the reader.

Specified by:

start in interface SourceReader<O,SplitT extends IteratorSourceSplit<E,IterT>>

start

protected void start(SourceReaderContext context)

pollNext

public InputStatus pollNext(ReaderOutput<O> output)

Description copied from interface: SourceReader

Poll the next available record into the ReaderOutput.

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

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

Specified by:

pollNext in interface SourceReader<O,SplitT extends IteratorSourceSplit<E,IterT>>

Returns:

The InputStatus of the SourceReader after the method invocation.

convert

protected abstract O convert(E value)

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 method returns a status other than InputStatus.MORE_AVAILABLE. After that, 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<O,SplitT extends IteratorSourceSplit<E,IterT>>

Returns:

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

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<O,SplitT extends IteratorSourceSplit<E,IterT>>

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<O,SplitT extends IteratorSourceSplit<E,IterT>>

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<O,SplitT extends IteratorSourceSplit<E,IterT>>

Returns:

the state of the source.

close

public void close()
           throws Exception

Specified by:

close in interface AutoCloseable

Throws:

Exception