We have a situation on Infinispan where closing an index backend blocks forever with the stack trace attached. We are not sure of the reason why since it is blocking on

at java.util.concurrent.ThreadPoolExecutor.awaitTermination(ThreadPoolExecutor.java:1465)
at org.hibernate.search.backend.impl.lucene.LuceneBackendResources.flushCloseExecutor(LuceneBackendResources.java:125)

but there are not threads running called "Index updates queue processor for index ...".