org.apache.flink.streaming.api.functions.source

接口 SourceFunction.SourceContext<T>

类型参数:

T - The type of the elements produced by the source.

封闭接口:

SourceFunction<T>

@Public
public static interface SourceFunction.SourceContext<T>

Interface that source functions use to emit elements, and possibly watermarks.

方法概要

限定符和类型	方法和说明
void	close() This method is called by the system to shut down the context.
void	collect(T element) Emits one element from the source, without attaching a timestamp.
void	collectWithTimestamp(T element, long timestamp) Emits one element from the source, and attaches the given timestamp.
void	emitWatermark(Watermark mark) Emits the given Watermark.
Object	getCheckpointLock() Returns the checkpoint lock.
void	markAsTemporarilyIdle() Marks the source to be temporarily idle.

方法详细资料

collect

void collect(T element)

Emits one element from the source, without attaching a timestamp. In most cases, this is the default way of emitting elements.

The timestamp that the element will get assigned depends on the time characteristic of the streaming program:

• On TimeCharacteristic.ProcessingTime, the element has no timestamp.
• On TimeCharacteristic.IngestionTime, the element gets the system's current time as the timestamp.
• On TimeCharacteristic.EventTime, the element will have no timestamp initially. It needs to get a timestamp (via a TimestampAssigner) before any time-dependent operation (like time windows).

参数:

element - The element to emit

collectWithTimestamp

@PublicEvolving
void collectWithTimestamp(T element,
                                          long timestamp)

Emits one element from the source, and attaches the given timestamp. This method is relevant for programs using TimeCharacteristic.EventTime, where the sources assign timestamps themselves, rather than relying on a TimestampAssigner on the stream.

On certain time characteristics, this timestamp may be ignored or overwritten. This allows programs to switch between the different time characteristics and behaviors without changing the code of the source functions.

• On TimeCharacteristic.ProcessingTime, the timestamp will be ignored, because processing time never works with element timestamps.
• On TimeCharacteristic.IngestionTime, the timestamp is overwritten with the system's current time, to realize proper ingestion time semantics.
• On TimeCharacteristic.EventTime, the timestamp will be used.

参数:

element - The element to emit

timestamp - The timestamp in milliseconds since the Epoch

emitWatermark

@PublicEvolving
void emitWatermark(Watermark mark)

Emits the given Watermark. A Watermark of value t declares that no elements with a timestamp t' <= t will occur any more. If further such elements will be emitted, those elements are considered late.

This method is only relevant when running on TimeCharacteristic.EventTime. On TimeCharacteristic.ProcessingTime,Watermarks will be ignored. On TimeCharacteristic.IngestionTime, the Watermarks will be replaced by the automatic ingestion time watermarks.

参数:

mark - The Watermark to emit

markAsTemporarilyIdle

@PublicEvolving
void markAsTemporarilyIdle()

Marks the source to be temporarily idle. This tells the system that this source will temporarily stop emitting records and watermarks for an indefinite amount of time. This is only relevant when running on TimeCharacteristic.IngestionTime and TimeCharacteristic.EventTime, allowing downstream tasks to advance their watermarks without the need to wait for watermarks from this source while it is idle.

Source functions should make a best effort to call this method as soon as they acknowledge themselves to be idle. The system will consider the source to resume activity again once SourceContext#collect(T), SourceContext#collectWithTimestamp(T, long), or emitWatermark(Watermark) is called to emit elements or watermarks from the source.

getCheckpointLock

Object getCheckpointLock()

Returns the checkpoint lock. Please refer to the class-level comment in SourceFunction for details about how to write a consistent checkpointed source.

返回:

The object to use as the lock

close

void close()

This method is called by the system to shut down the context.