Github user ddebrunner commented on a diff in the pull request:
https://github.com/apache/incubator-quarks/pull/167#discussion_r71049736
--- Diff: api/topology/src/main/java/quarks/topology/TWindow.java ---
@@ -105,8 +129,85 @@ Licensed to the Apache Software Foundation (ASF) under
one
* @return A stream that contains the latest aggregations of
partitions in this window.
*/
<U> TStream<U> batch(BiFunction<List<T>, K, U> batcher);
+
+ /**
+ * Declares a stream that is a continuous, sliding,
+ * timer triggered aggregation of
+ * partitions in this window.
+ * <P>
+ * Periodically trigger an invocation of
+ * {@code aggregator.apply(tuples, key)}, where {@code tuples} is
+ * a {@code List<T>} containing all the tuples in the partition in
+ * insertion order from oldest to newest. The list is stable
+ * during the aggregator invocation.
+ * The list will be empty if the partition is empty.
+ * </P>
+ * <P>
+ * A non-null {@code aggregator} result is added to the returned
stream.
+ * </P>
+ * <P>
+ * Thus the returned stream will contain a sequence of tuples where the
+ * most recent tuple represents the most up to date aggregation of a
+ * partition.
+ *
+ * @param <U> Tuple type
+ * @param period how often to invoke the aggregator
+ * @param unit TimeUnit for {@code period}
+ * @param aggregator
+ * Logic to aggregation a partition.
+ * @return A stream that contains the latest aggregations of
partitions in this window.
+ *
+ * @see #aggregate(BiFunction)
+ */
+ <U> TStream<U> timedAggregate(long period, TimeUnit unit,
BiFunction<List<T>, K, U> aggregator);
--- End diff --
I was wondering if the continue sending updates even if nothing has changed
might be better handled by a separate operation, then it could be applied to
anything, rather than just a window.
Something like pass any input tuple to the output, but send the last tuple
if nothing has been received for the declared period.
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