NicoK commented on a change in pull request #31:
URL: https://github.com/apache/flink-training/pull/31#discussion_r695684798
##########
File path:
common/src/test/java/org/apache/flink/training/exercises/testing/TestSink.java
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@@ -0,0 +1,26 @@
+package org.apache.flink.training.exercises.testing;
+
+import org.apache.flink.streaming.api.functions.sink.SinkFunction;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class TestSink<OUT> implements SinkFunction<OUT> {
+
+ // must be static
+ public static final List VALUES = Collections.synchronizedList(new
ArrayList<>());
+
+ @Override
+ public void invoke(OUT value, Context context) {
+ VALUES.add(value);
+ }
+
+ public Iterable<OUT> results() {
+ return VALUES;
+ }
+
+ public void reset() {
+ VALUES.clear();
+ }
+}
Review comment:
I'm not that deep into the accumulator topic, but reading up on them in
the
[docs](https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/dev/datastream/user_defined_functions/#accumulators--counters)
and code, it looks like they are even able to synchronise when used from
different operator functions!
Seems safer than a static variable and can be used in parallel tests.
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