org.apache.flink.streaming.api.windowing.policy

Interface ActiveTriggerPolicy<DATA>

Type Parameters:

DATA - The data type which can be handled by this policy

All Superinterfaces:

Serializable, TriggerPolicy<DATA>

All Known Implementing Classes:

CloneableMultiTriggerPolicy, MultiTriggerPolicy, TimeTriggerPolicy

public interface ActiveTriggerPolicy<DATA>
extends TriggerPolicy<DATA>

This interface extends the TriggerPolicy interface with functionality for active triggers. Active triggers can act in two ways: 1) Whenever an element arrives at the operator, the preNotifyTrigger(Object) method gets called first. It can return zero ore more fake data points which will be added before the currently arrived real element gets processed. This allows to handle empty windows in time based windowing with an user defined Timestamp. Triggers are not called on fake datapoint. A fake datapoint is always considered as triggered. 2) An active trigger has a factory method for a runnable. This factory method gets called at the start up of the operator. The returned runnable will be executed in its own thread and can submit fake elements at any time through an ActiveTriggerCallback. This allows to have time based triggers based on any system internal time measure. Triggers are not called on fake datapoint. A fake datapoints is always considered as triggered.

Method Summary

Modifier and Type	Method and Description
Runnable	createActiveTriggerRunnable(ActiveTriggerCallback callback) This is the factory method for a runnable.
Object[]	preNotifyTrigger(DATA datapoint) Whenever an element arrives at the operator, the preNotifyTrigger(Object) method gets called first.

Methods inherited from interface org.apache.flink.streaming.api.windowing.policy.TriggerPolicy

notifyTrigger

Method Detail

preNotifyTrigger

Object[] preNotifyTrigger(DATA datapoint)

Whenever an element arrives at the operator, the preNotifyTrigger(Object) method gets called first. It can return zero ore more fake data points which will be added before the the currently arrived real element gets processed. This allows to handle empty windows in time based windowing with an user defined Timestamp. Triggers are not called on fake datapoints. A fake datapoint is always considered as triggered.

Parameters:

datapoint - the data point which arrived at the operator

Returns:

zero ore more fake data points which will be added before the the currently arrived real element gets processed.

createActiveTriggerRunnable

Runnable createActiveTriggerRunnable(ActiveTriggerCallback callback)

This is the factory method for a runnable. This factory method gets called at the start up of the operator. The returned runnable will be executed in its own thread and can submit fake elements at any time through an ActiveTriggerCallback. This allows to have time based triggers based on any system internal time measure. Triggers are not called on fake datapoints. A fake datapoint is always considered as triggered.

Parameters:

callback - A callback object which allows to add fake elements from within the returned Runnable.

Returns:

The runnable implementation or null in case there is no. In case an ActiveTriggerPolicy is used, it can implement own Runnable classes. Such Runnable classes will be executed as an own thread and can submit fake elements, to the element buffer at any time.