Index: hbase-hadoop1-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsRegionSourceImpl.java =================================================================== --- hbase-hadoop1-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsRegionSourceImpl.java (revision 1459787) +++ hbase-hadoop1-compat/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsRegionSourceImpl.java (working copy) @@ -83,7 +83,9 @@ @Override public void close() { closed = true; - agg.deregister(this); + synchronized (agg) { + agg.deregister(this); + } LOG.trace("Removing region Metrics: " + regionWrapper.getRegionName()); registry.removeMetric(regionPutKey);