ArrayIndexOutOfBoundsException in CollectionMetric.getValueAndReset()

[jnioche]

Caused by: java.lang.ArrayIndexOutOfBoundsException: 9
	at java.util.LinkedList.toArray(LinkedList.java:1053) ~[?:1.8.0_161]
	at java.util.LinkedList.addAll(LinkedList.java:408) ~[?:1.8.0_161]
	at java.util.LinkedList.addAll(LinkedList.java:387) ~[?:1.8.0_161]
	at java.util.LinkedList.<init>(LinkedList.java:119) ~[?:1.8.0_161]
	at com.digitalpebble.stormcrawler.util.CollectionMetric.getValueAndReset(CollectionMetric.java:35) ~[stormjar.jar:?]
	at org.apache.storm.daemon.executor$metrics_tick$fn__4899.invoke(executor.clj:345) ~[storm-core-1.2.1.jar:1.2.1]
	at clojure.core$map$fn__4553.invoke(core.clj:2622) ~[clojure-1.7.0.jar:?]

https://github.com/DigitalPebble/storm-crawler/blob/ce9134612bbfbf500adba6a89477b2597181d241/core/src/main/java/com/digitalpebble/stormcrawler/util/CollectionMetric.java#L35

The metric object is used by https://github.com/DigitalPebble/storm-crawler/blob/f6d51debfd2a5897015c388ee931b21570ea1f52/external/elasticsearch/src/main/java/com/digitalpebble/stormcrawler/elasticsearch/persistence/AbstractSpout.java#L146

My guess is that the spout instance is trying to add the list while it is being copied. We could simply add synchronized blocks to prevent concurrent access to the list.