[KAFKA-4950] ConcurrentModificationException when iterating over Kafka Metrics

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.10.1.1
• Fix Version/s: 1.0.3, 1.1.2, 2.0.1, 2.1.0
• Component/s: consumer
• Assignee: Sébastien Launay
• Reporter: Dumitru Postoronca
• Created: 25/Mar/17 15:08
• Updated: 08/Aug/18 22:45
• Resolved: 08/Aug/18 22:45

Description

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.

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)

// 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);
    }
}

Issue Links

• links to: GitHub Pull Request #3907
• links to: GitHub Pull Request #3907