HSEARCH-2012 Improve logging and default implementations

backends/jgroups/src/main/java/org/hibernate/search/backend/jgroups/impl/JGroupsBackendQueueProcessor.java

@@ -154,6 +154,9 @@ public void closeIndexWriter() {
 		if ( selectionStrategy.isIndexOwnerLocal() ) {
 			delegatedBackend.closeIndexWriter();
 		}
+		else {
+			log.debugf( "Not owning the index '%s' so ignoring request to release IndexWriter lock", indexName );
+		}
 	}
 
 	@Override

elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/impl/ElasticSearchBackendQueueProcessor.java

@@ -67,6 +67,6 @@ public void indexMappingChanged() {
 
 	@Override
 	public void closeIndexWriter() {
-		throw new UnsupportedOperationException();
+		// no-op
 	}
 }

elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/impl/ElasticSearchIndexManager.java

@@ -307,7 +307,7 @@ public LuceneWorkSerializer getSerializer() {
 
 	@Override
 	public void closeIndexWriter() {
-		throw new UnsupportedOperationException( "Access to IndexWriter not supported with ES IndexManager" );
+		// no-op
 	}
 
 	private SerializationProvider requestSerializationProvider() {

engine/src/main/java/org/hibernate/search/backend/impl/blackhole/BlackHoleBackendQueueProcessor.java

@@ -71,7 +71,7 @@ public void indexMappingChanged() {
 
 	@Override
 	public void closeIndexWriter() {
-		log.debug( "Closing IndexWriter" );
+		log.debug( "BlackHoleBackend requested to close the IndexWriter (no-op)" );
 	}
 
 }

engine/src/main/java/org/hibernate/search/util/logging/impl/Log.java

@@ -928,7 +928,6 @@ public interface Log extends BasicLogger {
 			+ "indexing backend for index '%s'. Some pending index writes might have been lost.")
 	void timedOutWaitingShutdown(String indexName);
 
-
 	@LogMessage(level = Level.DEBUG)
 	@Message(id = 304, value = "Closing index writer for IndexManager '%1$s'")
 	void closingIndexWriter(String indexName);