chia7712 commented on code in PR #22809:
URL: https://github.com/apache/kafka/pull/22809#discussion_r4222075394
##########
streams/src/main/java/org/apache/kafka/streams/state/internals/MeteredKeyValueStore.java:
##########
@@ -104,9 +98,7 @@ public class MeteredKeyValueStore<K, V>
private TaskId taskId;
private Sensor restoreSensor;
- protected LongAdder numOpenIterators = new LongAdder();
- protected NavigableSet<MeteredIterator> openIterators = new
ConcurrentSkipListSet<>(Comparator.comparingLong(MeteredIterator::startTimestamp));
-
+ protected final MeteredIteratorTracker iteratorTracker = new
MeteredIteratorTracker();
Review Comment:
package-private is more suitable for this variable
##########
streams/src/main/java/org/apache/kafka/streams/state/internals/MeteredIteratorTracker.java:
##########
@@ -0,0 +1,66 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.kafka.streams.state.internals;
+
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.NavigableSet;
+import java.util.NoSuchElementException;
+import java.util.concurrent.ConcurrentSkipListSet;
+import java.util.concurrent.atomic.LongAdder;
+
+final class MeteredIteratorTracker {
+
+ private final LongAdder numOpenIterators;
+ private final NavigableSet<MeteredIterator> openIterators;
+
+ MeteredIteratorTracker() {
+ this(
+ new LongAdder(),
+ new
ConcurrentSkipListSet<>(Comparator.comparingLong(MeteredIterator::startTimestamp))
+ );
+ }
+
+ MeteredIteratorTracker(final LongAdder numOpenIterators,
+ final NavigableSet<MeteredIterator> openIterators) {
+ this.numOpenIterators = numOpenIterators;
+ this.openIterators = openIterators;
+ }
+
+ void add(final MeteredIterator iterator) {
+ numOpenIterators.increment();
+ openIterators.add(iterator);
+ }
+
+ void remove(final MeteredIterator iterator) {
+ numOpenIterators.decrement();
+ openIterators.remove(iterator);
+ }
+
+ long numOpenIterators() {
+ return numOpenIterators.sum();
+ }
+
+ long oldestIteratorStartTimestamp() {
+ try {
+ final Iterator<MeteredIterator> iterator =
openIterators.iterator();
+ return iterator.hasNext() ? iterator.next().startTimestamp() : 0L;
+ } catch (final NoSuchElementException e) {
Review Comment:
I’m confused why we need this catch. If the set is thread-safe, the iterator
prefetches the next item when hasNext is called, IIRC, so next can’t throw
`NoSuchElementException`. If it is not thread-safe, it throws
`ConcurrentModificationException` instead, which this catch doesn’t cover
anyway.
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