LUCENE-3061: Open IndexWriter API to allow custom MergeScheduler implementation

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1098576 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -280,6 +280,10 @@ API Changes
 * LUCENE-2953: In addition to changes in 3.x, PriorityQueue#initialize(int)
   function was moved into the ctor. (Uwe Schindler, Yonik Seeley)
 
+* LUCENE-3061: IndexWriter's getNextMerge() and merge(OneMerge) are now public
+  (though @lucene.experimental), allowing for custom MergeScheduler 
+  implementations. (Shai Erera)
+
 New features
 
 * LUCENE-2604: Added RegexpQuery support to QueryParser. Regular expressions

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

@@ -1813,10 +1813,13 @@ public class IndexWriter implements Closeable {
     return mergingSegments;
   }
 
-  /** Expert: the {@link MergeScheduler} calls this method
-   *  to retrieve the next merge requested by the
-   *  MergePolicy */
-  synchronized MergePolicy.OneMerge getNextMerge() {
+  /**
+   * Expert: the {@link MergeScheduler} calls this method to retrieve the next
+   * merge requested by the MergePolicy
+   * 
+   * @lucene.experimental
+   */
+  public synchronized MergePolicy.OneMerge getNextMerge() {
     if (pendingMerges.size() == 0)
       return null;
     else {
@@ -2936,9 +2939,10 @@ public class IndexWriter implements Closeable {
   /**
    * Merges the indicated segments, replacing them in the stack with a
    * single segment.
+   * 
+   * @lucene.experimental
    */
-
-  final void merge(MergePolicy.OneMerge merge)
+  public final void merge(MergePolicy.OneMerge merge)
     throws CorruptIndexException, IOException {
 
     boolean success = false;

lucene/src/test/org/apache/lucene/TestMergeSchedulerExternal.java

@@ -19,17 +19,21 @@ package org.apache.lucene;
 import java.io.IOException;
 
 import org.apache.lucene.util.LuceneTestCase;
+import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.MockDirectoryWrapper;
+import org.apache.lucene.store.RAMDirectory;
+import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.LogMergePolicy;
 import org.apache.lucene.index.MergePolicy;
 import org.apache.lucene.index.ConcurrentMergeScheduler;
+import org.apache.lucene.index.MergeScheduler;
+import org.apache.lucene.index.MergePolicy.OneMerge;
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.document.Field;
 
-
 /**
  * Holds tests cases to verify external APIs are accessible
  * while not being in org.apache.lucene.index package.
@@ -106,4 +110,40 @@ public class TestMergeSchedulerExternal extends LuceneTestCase {
     assertTrue(excCalled);
     dir.close();
   }
+  
+  private static class ReportingMergeScheduler extends MergeScheduler {
+
+    @Override
+    public void merge(IndexWriter writer) throws CorruptIndexException, IOException {
+      OneMerge merge = null;
+      while ((merge = writer.getNextMerge()) != null) {
+        if (VERBOSE) {
+          System.out.println("executing merge " + merge.segString(writer.getDirectory()));
+        }
+        writer.merge(merge);
+      }
+    }
+
+    @Override
+    public void close() throws CorruptIndexException, IOException {}
+    
+  }
+
+  public void testCustomMergeScheduler() throws Exception {
+    // we don't really need to execute anything, just to make sure the custom MS
+    // compiles. But ensure that it can be used as well, e.g., no other hidden
+    // dependencies or something. Therefore, don't use any random API !
+    Directory dir = new RAMDirectory();
+    IndexWriterConfig conf = new IndexWriterConfig(TEST_VERSION_CURRENT, null);
+    conf.setMergeScheduler(new ReportingMergeScheduler());
+    IndexWriter writer = new IndexWriter(dir, conf);
+    writer.addDocument(new Document());
+    writer.commit(); // trigger flush
+    writer.addDocument(new Document());
+    writer.commit(); // trigger flush
+    writer.optimize();
+    writer.close();
+    dir.close();
+  }
+  
 }