nicktelford commented on code in PR #18771:
URL: https://github.com/apache/kafka/pull/18771#discussion_r1938340249
##########
streams/src/main/java/org/apache/kafka/streams/state/internals/MeteredKeyValueStore.java:
##########
@@ -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:
As far as I understand, "weakly consistent" means that two different
threads, constructing two different iterators over the structure would see a
view of the structure that is consistent with _each other_ even in the face of
additions or removals.
I'm not certain of the behaviour of an Iterator between `hasNext` and `next`
calls. I'm on my phone right now so can't check, but it's possible that
`hasNext` actually takes a reference to the next object that `next` then
returns. This is how `KeyValueIterator` works IIRC.
I think the only way to be sure would be to check in the JDK implementation
and hope they don't change it in the future.
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