Github user wenlong88 commented on a diff in the pull request:
https://github.com/apache/flink/pull/3438#discussion_r104334699
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/ProcessFunction.java
---
@@ -19,30 +19,35 @@
package org.apache.flink.streaming.api.functions;
import org.apache.flink.annotation.PublicEvolving;
-import org.apache.flink.api.common.functions.Function;
+import org.apache.flink.api.common.functions.AbstractRichFunction;
import org.apache.flink.streaming.api.TimeDomain;
import org.apache.flink.streaming.api.TimerService;
import org.apache.flink.util.Collector;
/**
* A function that processes elements of a stream.
*
- * <p>The function will be called for every element in the input stream
and can produce
- * zero or more output. The function can also query the time and set
timers. When
- * reacting to the firing of set timers the function can emit yet more
elements.
+ * <p>For every element in the input stream {@link #processElement(Object,
Context, Collector)}
+ * is invoked. This can produce zero or more elements as output.
Implementations can also
+ * query the time and set timers through the provided {@link Context}. For
firing timers
+ * {@link #onTimer(long, OnTimerContext, Collector)} will be invoked. This
can again produce
+ * zero or more elements as output and register further timers.
*
- * <p>The function will be called for every element in the input stream
and can produce
- * zero or more output elements. Contrary to the
- * {@link org.apache.flink.api.common.functions.FlatMapFunction}, this
function can also query
- * the time (both event and processing) and set timers, through the
provided {@link Context}.
- * When reacting to the firing of set timers the function can directly
emit a result, and/or
- * register a timer that will trigger an action in the future.
+ * <p><b>NOTE:</b> Access to keyed state and timers (which are also scoped
to a key) is only
+ * available if the {@code ProcessFunction} is applied on a {@code
KeyedStream}.
+ *
+ * <p><b>NOTE:</b> A {@code ProcessFunction} is always a
+ * {@link org.apache.flink.api.common.functions.RichFunction}. Therefore,
access to the
+ * {@link org.apache.flink.api.common.functions.RuntimeContext} as always
available and setup and
+ * teardown methods can be implemented. See
+ * {@link
org.apache.flink.api.common.functions.RichFunction#open(org.apache.flink.configuration.Configuration)}
+ * and {@link org.apache.flink.api.common.functions.RichFunction#close()}.
*
* @param <I> Type of the input elements.
* @param <O> Type of the output elements.
*/
@PublicEvolving
-public interface ProcessFunction<I, O> extends Function {
+public abstract class ProcessFunction<I, O> extends AbstractRichFunction {
--- End diff --
hi, changing form `interface` to `class` is incompatible on the user side.
Can't ProcessFunction just extend RichFunction?
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