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

Class RateLimitedSourceReader<E,SplitT extends SourceSplit>

java.lang.Object

org.apache.flink.api.connector.source.util.ratelimit.RateLimitedSourceReader<E,SplitT>

All Implemented Interfaces:

AutoCloseable, CheckpointListener, SourceReader<E,SplitT>

@Experimental
public class RateLimitedSourceReader<E,SplitT extends SourceSplit>
extends Object
implements SourceReader<E,SplitT>

Wraps the actual SourceReader and rate limits its data emission.

Constructor Summary

Constructors

Constructor and Description
RateLimitedSourceReader(SourceReader<E,SplitT> sourceReader, RateLimiter rateLimiter) Instantiates a new rate-limited source reader.

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()
CompletableFuture<Void>	isAvailable() Returns a future that signals that data is available from the reader.
void	notifyCheckpointComplete(long checkpointId) We have an empty default implementation here because most source readers do not have to implement the method.
void	notifyNoMoreSplits() This method is called when the reader is notified that it will not receive any further splits.
InputStatus	pollNext(ReaderOutput<E> 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.

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, pauseOrResumeSplits

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

notifyCheckpointAborted

Constructor Detail

RateLimitedSourceReader

public RateLimitedSourceReader(SourceReader<E,SplitT> sourceReader,
                               RateLimiter rateLimiter)

Instantiates a new rate-limited source reader.

Parameters:

sourceReader - The actual source reader.

rateLimiter - The rate limiter.

Method Detail

start

public void start()

Description copied from interface: SourceReader

Start the reader.

Specified by:

start in interface SourceReader<E,SplitT extends SourceSplit>

pollNext

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

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<E,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 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<E,SplitT extends SourceSplit>

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<E,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<E,SplitT extends SourceSplit>

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<E,SplitT extends SourceSplit>

Returns:

the state of the source.

close

public void close()
           throws Exception

Specified by:

close in interface AutoCloseable

Throws:

Exception

notifyCheckpointComplete

public void notifyCheckpointComplete(long checkpointId)
                              throws Exception

Description copied from interface: SourceReader

We have an empty default implementation here because most source readers do not have to implement the method.

Specified by:

notifyCheckpointComplete in interface CheckpointListener

Specified by:

notifyCheckpointComplete in interface SourceReader<E,SplitT extends SourceSplit>

Parameters:

checkpointId - The ID of the checkpoint that has been completed.

Throws:

Exception - This method can propagate exceptions, which leads to a failure/recovery for the task. Note that this will NOT lead to the checkpoint being revoked.

See Also:

CheckpointListener.notifyCheckpointComplete(long)