[ENGINE] try increment store before searcher is acquired

InternalEngine#refreshNeeded must increment the ref count on the
store used before it's checking if the searcher is current since
internally a searcher ref is acquired and if that happens concurrently
to a engine close it might violate the assumption that all files
are closed when the store is closed.

This commit also converts some try / finally into try / with.

src/main/java/org/elasticsearch/index/engine/internal/InternalEngine.java

@@ -361,7 +361,7 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
             }
 
             // no version, get the version from the index, we know that we refresh on flush
-            Searcher searcher = acquireSearcher("get");
+            final Searcher searcher = acquireSearcher("get");
             final Versions.DocIdAndVersion docIdAndVersion;
             try {
                 docIdAndVersion = Versions.loadDocIdAndVersion(searcher.reader(), get.uid());
@@ -737,6 +737,13 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
 
     @Override
     public boolean refreshNeeded() {
+        if (store.tryIncRef()) {
+            /*
+              we need to inc the store here since searcherManager.isSearcherCurrent()
+              acquires a searcher internally and that might keep a file open on the
+              store. this violates the assumption that all files are closed when
+              the store is closed so we need to make sure we increment it here
+             */
             try {
                 // we are either dirty due to a document added or due to a
                 // finished merge - either way we should refresh
@@ -745,8 +752,12 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
                 logger.error("failed to access searcher manager", e);
                 failEngine("failed to access searcher manager", e);
                 throw new EngineException(shardId, "failed to access searcher manager", e);
+            } finally {
+                store.decRef();
             }
         }
+        return false;
+    }
 
     @Override
     public boolean possibleMergeNeeded() {
@@ -1158,8 +1169,7 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
     public SegmentsStats segmentsStats() {
         try (InternalLock _ = readLock.acquire()) {
             ensureOpen();
-            Searcher searcher = acquireSearcher("segments_stats");
-            try {
+            try (final Searcher searcher = acquireSearcher("segments_stats")) {
                 SegmentsStats stats = new SegmentsStats();
                 for (AtomicReaderContext reader : searcher.reader().leaves()) {
                     stats.add(1, getReaderRamBytesUsed(reader));
@@ -1168,8 +1178,6 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
                 stats.addIndexWriterMemoryInBytes(indexWriter.ramBytesUsed());
                 stats.addIndexWriterMaxMemoryInBytes((long) (indexWriter.getConfig().getRAMBufferSizeMB()*1024*1024));
                 return stats;
-            } finally {
-                searcher.close();
             }
         }
     }
@@ -1355,11 +1363,8 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
     }
 
     private long loadCurrentVersionFromIndex(Term uid) throws IOException {
-        Searcher searcher = acquireSearcher("load_version");
-        try {
+        try (final Searcher searcher = acquireSearcher("load_version")) {
             return Versions.loadVersion(searcher.reader(), uid);
-        } finally {
-            searcher.close();
         }
     }
 
@@ -1573,7 +1578,6 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
             if (warmer != null) {
                 // we need to pass a custom searcher that does not release anything on Engine.Search Release,
                 // we will release explicitly
-                Searcher currentSearcher = null;
                 IndexSearcher newSearcher = null;
                 boolean closeNewSearcher = false;
                 try {
@@ -1581,7 +1585,7 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
                         // fresh index writer, just do on all of it
                         newSearcher = searcher;
                     } else {
-                        currentSearcher = acquireSearcher("search_factory");
+                        try (final Searcher currentSearcher = acquireSearcher("search_factory")) {
                             // figure out the newSearcher, with only the new readers that are relevant for us
                             List<IndexReader> readers = Lists.newArrayList();
                             for (AtomicReaderContext newReaderContext : searcher.getIndexReader().leaves()) {
@@ -1606,6 +1610,7 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
                                 closeNewSearcher = true;
                             }
                         }
+                    }
 
                     if (newSearcher != null) {
                         IndicesWarmer.WarmerContext context = new IndicesWarmer.WarmerContext(shardId, new SimpleSearcher("warmer", newSearcher));
@@ -1618,7 +1623,6 @@ public class InternalEngine extends AbstractIndexShardComponent implements Engin
                     }
                 } finally {
                     // no need to release the fullSearcher, nothing really is done...
-                    Releasables.close(currentSearcher);
                     if (newSearcher != null && closeNewSearcher) {
                         IOUtils.closeWhileHandlingException(newSearcher.getIndexReader()); // ignore
                     }