mjsax commented on code in PR #18771:
URL: https://github.com/apache/kafka/pull/18771#discussion_r1938344950
##########
streams/src/main/java/org/apache/kafka/streams/state/internals/MeteredKeyValueStore.java:
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@@ -156,11 +156,8 @@ private void registerMetrics() {
(config, now) -> numOpenIterators.sum());
StateStoreMetrics.addOldestOpenIteratorGauge(taskId.toString(),
metricsScope, name(), streamsMetrics,
(config, now) -> {
- try {
- return openIterators.isEmpty() ? null :
openIterators.first().startTimestamp();
- } catch (final NoSuchElementException ignored) {
- return null;
- }
+ final Iterator<MeteredIterator> openIteratorsIterator =
openIterators.iterator();
+ return openIteratorsIterator.hasNext() ?
openIteratorsIterator.next().startTimestamp() : null;
Review Comment:
https://stackoverflow.com/questions/28915215/iterator-type-in-java-weakly-consistent
Somewhat old, and refers to Java 8 only.
Not sure how to read this one:
> What this doesn't say (and what may be implicit in the use of the word
"consistent") is that iteration won't result in an error such as
IndexOutOfBoundsException or NoSuchElementException [..] The third bullet in
particular explicitly doesn't make any guarantees about what elements are seen
by the iteration if modifications occur during iteration.
Also:
> Weakly consistent iteration provides guarantees against repeated elements
and against a variety of errors or infinite loops that can occur. The
"weakness" is that they provide few guarantees about exactly which elements are
observed during iteration.
In the end, I can only infer that we don't know what elements we get back.
It seems not to be conclusive about `hasNext/next` guarantees / safety.
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