Fix not to perform clean up during scan

(#1550)

airsonic-main/src/main/java/org/airsonic/player/controller/MusicFolderSettingsController.java

@@ -101,20 +101,28 @@ public class MusicFolderSettingsController {
     }
 
 
-    private void expunge() {
+    private synchronized void expunge() {
+
+        MediaLibraryStatistics statistics = indexManager.getStatistics();
+
+        /*
+         * indexManager#expunge depends on DB delete flag.
+         * For consistency, clean of DB and Lucene must run in one block.
+         *
+         * Lucene's writing is exclusive.
+         * This process cannot be performed
+         * while during scan or scan has never been performed.
+         */
+        if (statistics != null && !mediaScannerService.isScanning()) {
 
             // to be before dao#expunge
-        MediaLibraryStatistics statistics = indexManager.getStatistics();
-        if (statistics != null) {
             LOG.debug("Cleaning search index...");
             indexManager.startIndexing();
             indexManager.expunge();
             indexManager.stopIndexing(statistics);
             LOG.debug("Search index cleanup complete.");
-        } else {
-            LOG.warn("Missing index statistics - index probably hasn't been created yet. Not expunging index.");
-        }
 
+            // to be after indexManager#expunge
             LOG.debug("Cleaning database...");
             LOG.debug("Deleting non-present artists...");
             artistDao.expunge();
@@ -124,6 +132,10 @@ public class MusicFolderSettingsController {
             mediaFileDao.expunge();
             LOG.debug("Database cleanup complete.");
             mediaFileDao.checkpoint();
+
+        } else {
+            LOG.warn("Index hasn't been created yet or during scanning. Plese execute clean up after scan is completed.");
+        }
     }
 
     private List<MusicFolderSettingsCommand.MusicFolderInfo> wrap(List<MusicFolder> musicFolders) {

airsonic-main/src/main/java/org/airsonic/player/service/search/IndexManager.java

@@ -313,8 +313,10 @@ public class IndexManager {
                 }
             } catch (IndexNotFoundException e) {
                 LOG.debug("Index {} does not exist in {}, likely not yet created.", indexType.toString(), indexDirectory.getAbsolutePath());
+                return null;
             } catch (IOException e) {
                 LOG.warn("Failed to initialize SearcherManager.", e);
+                return null;
             }
         }
         try {