LUCENE-7983: IndexWriter.IndexReaderWarmer is now a functional interface instead of an abstract class with a single method.

lucene/CHANGES.txt

@@ -106,6 +106,10 @@ Other
 * LUCENE-7978: Add some more documentation about setting up build
   environment.  (Anton R. Yuste via Uwe Schindler)
 
+* LUCENE-7983: IndexWriter.IndexReaderWarmer is now a functional interface
+  instead of an abstract class with a single method (Dawid Weiss)
+
+
 ======================= Lucene 7.0.1 =======================
 (No Changes)
 

lucene/core/src/java/org/apache/lucene/index/IndexWriter.java

@@ -4804,19 +4804,16 @@ public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
    *
    * @lucene.experimental
    *
-   * <p><b>NOTE</b>: warm is called before any deletes have
+   * <p><b>NOTE</b>: {@link #warm(LeafReader)} is called before any
-   * been carried over to the merged segment. */
+   * deletes have been carried over to the merged segment. */
-  public static abstract class IndexReaderWarmer {
+  @FunctionalInterface
-
+  public static interface IndexReaderWarmer {
-    /** Sole constructor. (For invocation by subclass 
+    /**
-     *  constructors, typically implicit.) */
+     * Invoked on the {@link LeafReader} for the newly
-    protected IndexReaderWarmer() {
+     * merged segment, before that segment is made visible
-    }
+     * to near-real-time readers.
-
+     */
-    /** Invoked on the {@link LeafReader} for the newly
+    void warm(LeafReader reader) throws IOException;
-     *  merged segment, before that segment is made visible
-     *  to near-real-time readers. */
-    public abstract void warm(LeafReader reader) throws IOException;
   }
 
   void tragicEvent(Throwable tragedy, String location) throws IOException {

lucene/core/src/java/org/apache/lucene/index/SimpleMergedSegmentWarmer.java

@@ -26,9 +26,9 @@ import org.apache.lucene.util.InfoStream;
  * A very simple merged segment warmer that just ensures 
  * data structures are initialized.
  */
-public class SimpleMergedSegmentWarmer extends IndexReaderWarmer {
+public class SimpleMergedSegmentWarmer implements IndexReaderWarmer {
   private final InfoStream infoStream;
-  
+
   /**
    * Creates a new SimpleMergedSegmentWarmer
    * @param infoStream InfoStream to log statistics about warming.
@@ -53,7 +53,7 @@ public class SimpleMergedSegmentWarmer extends IndexReaderWarmer {
           normsCount++;
         }
       }
-      
+
       if (info.getDocValuesType() != DocValuesType.NONE) {
         switch(info.getDocValuesType()) {
           case NUMERIC:

lucene/core/src/test/org/apache/lucene/index/TestDemoParallelLeafReader.java

@@ -129,17 +129,14 @@ public class TestDemoParallelLeafReader extends LuceneTestCase {
       }
       w = new IndexWriter(indexDir, iwc);
 
-      w.getConfig().setMergedSegmentWarmer(new IndexWriter.IndexReaderWarmer() {
+      w.getConfig().setMergedSegmentWarmer((reader) -> {
-          @Override
+        // This will build the parallel index for the merged segment before the merge becomes visible, so reopen delay is only due to
-          public void warm(LeafReader reader) throws IOException {
+        // newly flushed segments:
-            // This will build the parallel index for the merged segment before the merge becomes visible, so reopen delay is only due to
+        if (DEBUG) System.out.println(Thread.currentThread().getName() +": TEST: now warm " + reader);
-            // newly flushed segments:
+        // TODO: it's not great that we pass false here; it means we close the reader & reopen again for NRT reader; still we did "warm" by
-            if (DEBUG) System.out.println(Thread.currentThread().getName() +": TEST: now warm " + reader);
+        // building the parallel index, if necessary
-            // TODO: it's not great that we pass false here; it means we close the reader & reopen again for NRT reader; still we did "warm" by
+        getParallelLeafReader(reader, false, getCurrentSchemaGen());
-            // building the parallel index, if necessary
+      });
-            getParallelLeafReader(reader, false, getCurrentSchemaGen());
-          }
-        });
 
       // start with empty commit:
       w.commit();

lucene/core/src/test/org/apache/lucene/index/TestIndexWriterReader.java

@@ -612,24 +612,15 @@ public class TestIndexWriterReader extends LuceneTestCase {
     }
   }
 
-  private static class MyWarmer extends IndexWriter.IndexReaderWarmer {
-    int warmCount;
-    @Override
-    public void warm(LeafReader reader) throws IOException {
-      warmCount++;
-    }
-  }
-
   public void testMergeWarmer() throws Exception {
-
     Directory dir1 = getAssertNoDeletesDirectory(newDirectory());
     // Enroll warmer
-    MyWarmer warmer = new MyWarmer();
+    AtomicInteger warmCount = new AtomicInteger();
     IndexWriter writer = new IndexWriter(
         dir1,
         newIndexWriterConfig(new MockAnalyzer(random()))
           .setMaxBufferedDocs(2)
-          .setMergedSegmentWarmer(warmer)
+          .setMergedSegmentWarmer((leafReader) -> warmCount.incrementAndGet())
           .setMergeScheduler(new ConcurrentMergeScheduler())
           .setMergePolicy(newLogMergePolicy())
     );
@@ -648,12 +639,12 @@ public class TestIndexWriterReader extends LuceneTestCase {
     }
     ((ConcurrentMergeScheduler) writer.getConfig().getMergeScheduler()).sync();
 
-    assertTrue(warmer.warmCount > 0);
+    assertTrue(warmCount.get() > 0);
-    final int count = warmer.warmCount;
+    final int count = warmCount.get();
 
     writer.addDocument(DocHelper.createDocument(17, "test", 4));
     writer.forceMerge(1);
-    assertTrue(warmer.warmCount > count);
+    assertTrue(warmCount.get() > count);
     
     writer.close();
     r1.close();
@@ -969,24 +960,21 @@ public class TestIndexWriterReader extends LuceneTestCase {
     final AtomicBoolean didWarm = new AtomicBoolean();
     IndexWriter w = new IndexWriter(
         dir,
-        newIndexWriterConfig(new MockAnalyzer(random())).
+        newIndexWriterConfig(new MockAnalyzer(random()))
-            setMaxBufferedDocs(2).
+           .setMaxBufferedDocs(2)
-            setReaderPooling(true).
+           .setReaderPooling(true)
-            setMergedSegmentWarmer(new IndexWriter.IndexReaderWarmer() {
+           .setMergedSegmentWarmer((r) -> {
-              @Override
+              IndexSearcher s = newSearcher(r);
-              public void warm(LeafReader r) throws IOException {
+              TopDocs hits = s.search(new TermQuery(new Term("foo", "bar")), 10);
-                IndexSearcher s = newSearcher(r);
+              assertEquals(20, hits.totalHits);
-                TopDocs hits = s.search(new TermQuery(new Term("foo", "bar")), 10);
+              didWarm.set(true);
-                assertEquals(20, hits.totalHits);
+           })
-                didWarm.set(true);
+           .setMergePolicy(newLogMergePolicy(10))
-              }
-            }).
-            setMergePolicy(newLogMergePolicy(10))
     );
 
     Document doc = new Document();
     doc.add(newStringField("foo", "bar", Field.Store.NO));
-    for(int i=0;i<20;i++) {
+    for (int i = 0; i < 20; i++) {
       w.addDocument(doc);
     }
     w.waitForMerges();

lucene/replicator/src/java/org/apache/lucene/replicator/nrt/PreCopyMergedSegmentWarmer.java

@@ -34,7 +34,7 @@ import org.apache.lucene.index.SegmentReader;
 
 // TODO: or ... replica node can do merging locally?  tricky to keep things in sync, when one node merges more slowly than others...
 
-class PreCopyMergedSegmentWarmer extends IndexReaderWarmer {
+class PreCopyMergedSegmentWarmer implements IndexReaderWarmer {
 
   private final PrimaryNode primary;
 
@@ -48,7 +48,7 @@ class PreCopyMergedSegmentWarmer extends IndexReaderWarmer {
     final SegmentCommitInfo info = ((SegmentReader) reader).getSegmentInfo();
     //System.out.println("TEST: warm merged segment files " + info);
     Map<String,FileMetaData> filesMetaData = new HashMap<>();
-    for(String fileName : info.files()) {
+    for (String fileName : info.files()) {
       FileMetaData metaData = primary.readLocalFileMetaData(fileName);
       assert metaData != null;
       assert filesMetaData.containsKey(fileName) == false;

lucene/test-framework/src/java/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java

@@ -16,7 +16,6 @@
  */
 package org.apache.lucene.index;
 
-import java.io.IOException;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -468,32 +467,29 @@ public abstract class ThreadedIndexingAndSearchingTestCase extends LuceneTestCas
       mp.setNoCFSRatio(Math.max(0.25d, mp.getNoCFSRatio()));
     }
 
-    conf.setMergedSegmentWarmer(new IndexWriter.IndexReaderWarmer() {
+    conf.setMergedSegmentWarmer((reader) -> {
-      @Override
+      if (VERBOSE) {
-      public void warm(LeafReader reader) throws IOException {
+        System.out.println("TEST: now warm merged reader=" + reader);
-        if (VERBOSE) {
+      }
-          System.out.println("TEST: now warm merged reader=" + reader);
+      warmed.put(((SegmentReader) reader).core, Boolean.TRUE);
-        }
+      final int maxDoc = reader.maxDoc();
-        warmed.put(((SegmentReader) reader).core, Boolean.TRUE);
+      final Bits liveDocs = reader.getLiveDocs();
-        final int maxDoc = reader.maxDoc();
+      int sum = 0;
-        final Bits liveDocs = reader.getLiveDocs();
+      final int inc = Math.max(1, maxDoc/50);
-        int sum = 0;
+      for(int docID=0;docID<maxDoc;docID += inc) {
-        final int inc = Math.max(1, maxDoc/50);
+        if (liveDocs == null || liveDocs.get(docID)) {
-        for(int docID=0;docID<maxDoc;docID += inc) {
+          final Document doc = reader.document(docID);
-          if (liveDocs == null || liveDocs.get(docID)) {
+          sum += doc.getFields().size();
-            final Document doc = reader.document(docID);
-            sum += doc.getFields().size();
-          }
-        }
-
-        IndexSearcher searcher = newSearcher(reader, false);
-        sum += searcher.search(new TermQuery(new Term("body", "united")), 10).totalHits;
-
-        if (VERBOSE) {
-          System.out.println("TEST: warm visited " + sum + " fields");
         }
       }
-      });
+
+      IndexSearcher searcher = newSearcher(reader, false);
+      sum += searcher.search(new TermQuery(new Term("body", "united")), 10).totalHits;
+
+      if (VERBOSE) {
+        System.out.println("TEST: warm visited " + sum + " fields");
+      }
+    });
 
     if (VERBOSE) {
       conf.setInfoStream(new PrintStreamInfoStream(System.out) {