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https://issues.apache.org/jira/browse/KAFKA-4950?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15977294#comment-15977294
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Dumitru Postoronca commented on KAFKA-4950:
-------------------------------------------
[~vahid]: updated description with whole class. The code is basically mapping
Kakfa metrics to Codahale metrics. I think the dependency version is
{{'io.dropwizard.metrics:metrics-core:3.1.2'}}.
The metrics library then calls the gauge.getValue() method every minute, to get
the current value, thus effectively executing {{e.getValue().value()}}.
> ConcurrentModificationException when iterating over Kafka Metrics
> -----------------------------------------------------------------
>
> Key: KAFKA-4950
> URL: https://issues.apache.org/jira/browse/KAFKA-4950
> Project: Kafka
> Issue Type: Bug
> Affects Versions: 0.10.1.1
> Reporter: Dumitru Postoronca
> Assignee: Vahid Hashemian
> Priority: Minor
> Fix For: 0.11.0.0
>
>
> It looks like the when calling {{PartitionStates.partitionSet()}}, while the
> resulting Hashmap is being built, the internal state of the allocations can
> change, which leads to ConcurrentModificationException during the copy
> operation.
> {code}
> java.util.ConcurrentModificationException
> at
> java.util.LinkedHashMap$LinkedHashIterator.nextNode(LinkedHashMap.java:719)
> at
> java.util.LinkedHashMap$LinkedKeyIterator.next(LinkedHashMap.java:742)
> at java.util.AbstractCollection.addAll(AbstractCollection.java:343)
> at java.util.HashSet.<init>(HashSet.java:119)
> at
> org.apache.kafka.common.internals.PartitionStates.partitionSet(PartitionStates.java:66)
> at
> org.apache.kafka.clients.consumer.internals.SubscriptionState.assignedPartitions(SubscriptionState.java:291)
> at
> org.apache.kafka.clients.consumer.internals.ConsumerCoordinator$ConsumerCoordinatorMetrics$1.measure(ConsumerCoordinator.java:783)
> at
> org.apache.kafka.common.metrics.KafkaMetric.value(KafkaMetric.java:61)
> at
> org.apache.kafka.common.metrics.KafkaMetric.value(KafkaMetric.java:52)
> {code}
> {code}
> // client code:
> import java.util.Collections;
> import java.util.HashMap;
> import java.util.Map;
> import com.codahale.metrics.Gauge;
> import com.codahale.metrics.Metric;
> import com.codahale.metrics.MetricSet;
> import org.apache.kafka.clients.consumer.KafkaConsumer;
> import org.apache.kafka.common.MetricName;
> import static com.codahale.metrics.MetricRegistry.name;
> public class KafkaMetricSet implements MetricSet {
> private final KafkaConsumer client;
> public KafkaMetricSet(KafkaConsumer client) {
> this.client = client;
> }
> @Override
> public Map<String, Metric> getMetrics() {
> final Map<String, Metric> gauges = new HashMap<String, Metric>();
> Map<MetricName, org.apache.kafka.common.Metric> m = client.metrics();
> for (Map.Entry<MetricName, org.apache.kafka.common.Metric> e :
> m.entrySet()) {
> gauges.put(name(e.getKey().group(), e.getKey().name(), "count"),
> new Gauge<Double>() {
> @Override
> public Double getValue() {
> return e.getValue().value(); // exception thrown here
> }
> });
> }
> return Collections.unmodifiableMap(gauges);
> }
> }
> {code}
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