org.apache.flink.streaming.runtime.operators.windowing

Class MergingWindowSet<W extends Window>

java.lang.Object

org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSet<W>

Type Parameters:

W - The type of Window that this set is keeping track of.

public class MergingWindowSet<W extends Window>
extends Object

Utility for keeping track of merging Windows when using a MergingWindowAssigner in a WindowOperator.

When merging windows, we keep one of the original windows as the state window, i.e. the window that is used as namespace to store the window elements. Elements from the state windows of merged windows must be merged into this one state window. We keep a mapping from in-flight window to state window that can be queried using getStateWindow(Window).

A new window can be added to the set of in-flight windows using addWindow(Window, MergeFunction). This might merge other windows and the caller must react accordingly in the MergingWindowSet.MergeFunction.merge(Object, Collection, Object, Collection) and adjust the outside view of windows and state.

Windows can be removed from the set of windows using retireWindow(Window).

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	MergingWindowSet.MergeFunction<W> Callback for addWindow(Window, MergeFunction).

Constructor Summary

Constructors

Constructor and Description
MergingWindowSet(MergingWindowAssigner<?,W> windowAssigner, ListState<Tuple2<W,W>> state) Restores a MergingWindowSet from the given state.

Method Summary

Modifier and Type	Method and Description
W	addWindow(W newWindow, MergingWindowSet.MergeFunction<W> mergeFunction) Adds a new Window to the set of in-flight windows.
W	getStateWindow(W window) Returns the state window for the given in-flight Window.
void	persist() Persist the updated mapping to the given state if the mapping changed since initialization.
void	retireWindow(W window) Removes the given window from the set of in-flight windows.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

MergingWindowSet

public MergingWindowSet(MergingWindowAssigner<?,W> windowAssigner,
                        ListState<Tuple2<W,W>> state)
                 throws Exception

Restores a MergingWindowSet from the given state.

Throws:

Exception

Method Detail

persist

public void persist()
             throws Exception

Persist the updated mapping to the given state if the mapping changed since initialization.

Throws:

Exception

getStateWindow

public W getStateWindow(W window)

Returns the state window for the given in-flight Window. The state window is the Window in which we keep the actual state of a given in-flight window. Windows might expand but we keep to original state window for keeping the elements of the window to avoid costly state juggling.

Parameters:

window - The window for which to get the state window.

retireWindow

public void retireWindow(W window)

Removes the given window from the set of in-flight windows.

Parameters:

window - The Window to remove.

addWindow

public W addWindow(W newWindow,
                   MergingWindowSet.MergeFunction<W> mergeFunction)
            throws Exception

Adds a new Window to the set of in-flight windows. It might happen that this triggers merging of previously in-flight windows. In that case, the provided MergingWindowSet.MergeFunction is called.

This returns the window that is the representative of the added window after adding. This can either be the new window itself, if no merge occurred, or the newly merged window. Adding an element to a window or calling trigger functions should only happen on the returned representative. This way, we never have to deal with a new window that is immediately swallowed up by another window.

If the new window is merged, the MergeFunction callback arguments also don't contain the new window as part of the list of merged windows.

Parameters:

newWindow - The new Window to add.

mergeFunction - The callback to be invoked in case a merge occurs.

Returns:

The Window that new new Window ended up in. This can also be the the new Window itself in case no merge occurred.

Throws:

Exception

toString

public String toString()

Overrides:

toString in class Object