Index: lucene/contrib/misc/src/test/org/apache/lucene/search/TestSearcherManager.java
===================================================================
--- lucene/contrib/misc/src/test/org/apache/lucene/search/TestSearcherManager.java	(revision 1183650)
+++ lucene/contrib/misc/src/test/org/apache/lucene/search/TestSearcherManager.java	(working copy)
@@ -18,16 +18,17 @@
  */
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
-import java.util.List;
-import java.util.ArrayList;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Document;
+import org.apache.lucene.index.ConcurrentMergeScheduler;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.ThreadedIndexingAndSearchingTestCase;
@@ -63,7 +64,6 @@
 
   @Override
   protected void doAfterWriter(ExecutorService es) throws Exception {
-    // SearcherManager needs to see empty commit:
     final SearcherWarmer warmer = new SearcherWarmer() {
       @Override
       public void warm(IndexSearcher s) throws IOException {
@@ -75,6 +75,7 @@
       mgr = SearcherManager.open(writer, true, warmer, es);
       isNRT = true;
     } else {
+      // SearcherManager needs to see empty commit:
       writer.commit();
       mgr = SearcherManager.open(dir, warmer, es);
       isNRT = false;
@@ -178,8 +179,9 @@
   
   public void testIntermediateClose() throws IOException, InterruptedException {
     Directory dir = newDirectory();
+    // Test can deadlock if we use SMS:
     IndexWriter writer = new IndexWriter(dir, newIndexWriterConfig(
-        TEST_VERSION_CURRENT, new MockAnalyzer(random)));
+                                                                   TEST_VERSION_CURRENT, new MockAnalyzer(random)).setMergeScheduler(new ConcurrentMergeScheduler()));
     writer.addDocument(new Document());
     writer.commit();
     final CountDownLatch awaitEnterWarm = new CountDownLatch(1);
Index: lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherLifetimeManager.java
===================================================================
--- lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherLifetimeManager.java	(revision 1183650)
+++ lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherLifetimeManager.java	(working copy)
@@ -173,8 +173,8 @@
         // incRef done by SearcherTracker ctor:
         tracker.close();
       }
-    } else {
-      assert tracker.searcher == searcher;
+    } else if (tracker.searcher != searcher) {
+      throw new IllegalArgumentException("the provided searcher has the same underlying reader version yet the searcher instance differs from before (new=" + searcher + " vs old=" + tracker.searcher);
     }
 
     return version;
Index: lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherManager.java
===================================================================
--- lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherManager.java	(revision 1183650)
+++ lucene/contrib/misc/src/java/org/apache/lucene/search/SearcherManager.java	(working copy)
@@ -292,7 +292,7 @@
     @Override
     protected IndexReader openIfChanged(IndexReader oldReader)
         throws IOException {
-      return IndexReader.openIfChanged(oldReader, writer, applyDeletes);
+      return IndexReader.openIfChanged(oldReader, applyDeletes);
     }
   }
 
Index: lucene/src/test/org/apache/lucene/search/TestCachingWrapperFilter.java
===================================================================
--- lucene/src/test/org/apache/lucene/search/TestCachingWrapperFilter.java	(revision 1183650)
+++ lucene/src/test/org/apache/lucene/search/TestCachingWrapperFilter.java	(working copy)
@@ -235,10 +235,9 @@
 
     // make sure we get a cache hit when we reopen reader
     // that had no change to deletions
+    writer.deleteDocuments(new Term("foo", "bar"));
     reader = refreshReader(reader);
-    assertTrue(reader != oldReader);
-    searcher.close();
-    searcher = newSearcher(reader, false);
+    assertTrue(reader == oldReader);
     int missCount = filter.missCount;
     docs = searcher.search(constantScore, 1);
     assertEquals("[just filter] Should find a hit...", 1, docs.totalHits);
Index: lucene/src/test/org/apache/lucene/search/TestCachingSpanFilter.java
===================================================================
--- lucene/src/test/org/apache/lucene/search/TestCachingSpanFilter.java	(revision 1183650)
+++ lucene/src/test/org/apache/lucene/search/TestCachingSpanFilter.java	(working copy)
@@ -116,10 +116,10 @@
 
     // make sure we get a cache hit when we reopen readers
     // that had no new deletions
+    // Deletes nothing:
+    writer.deleteDocuments(new Term("foo", "bar"));
     reader = refreshReader(reader);
-    assertTrue(reader != oldReader);
-    searcher.close();
-    searcher = newSearcher(reader, false);
+    assertTrue(reader == oldReader);
     int missCount = filter.missCount;
     docs = searcher.search(constantScore, 1);
     assertEquals("[just filter] Should find a hit...", 1, docs.totalHits);
Index: lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java
===================================================================
--- lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java	(revision 1183650)
+++ lucene/src/test/org/apache/lucene/index/TestIndexWriterReader.java	(working copy)
@@ -857,7 +857,7 @@
     int sum = 0;
     while(System.currentTimeMillis() < endTime) {
       IndexReader r2 = IndexReader.openIfChanged(r);
-      if (r2 != r) {
+      if (r2 != null) {
         r.close();
         r = r2;
       }
@@ -1016,4 +1016,40 @@
     }
   }
   
+  public void testReopenAfterNoRealChange() throws Exception {
+    Directory d = newDirectory();
+    IndexWriter w = new IndexWriter(
+        d,
+        newIndexWriterConfig(TEST_VERSION_CURRENT, new MockAnalyzer(random)));
+    w.setInfoStream(VERBOSE ? System.out : null);
+
+    IndexReader r = w.getReader(); // start pooling readers
+
+    IndexReader r2 = IndexReader.openIfChanged(r);
+    assertNull(r2);
+    
+    w.addDocument(new Document());
+    IndexReader r3 = IndexReader.openIfChanged(r);
+    assertNotNull(r3);
+    assertTrue(r3.getVersion() != r.getVersion());
+    assertTrue(r3.isCurrent());
+
+    // Deletes nothing in reality...:
+    w.deleteDocuments(new Term("foo", "bar"));
+
+    // ... but IW marks this as not current:
+    assertFalse(r3.isCurrent());
+    IndexReader r4 = IndexReader.openIfChanged(r3);
+    assertNull(r4);
+
+    // Deletes nothing in reality...:
+    w.deleteDocuments(new Term("foo", "bar"));
+    IndexReader r5 = IndexReader.openIfChanged(r3, w, true);
+    assertNull(r5);
+
+    r3.close();
+
+    w.close();
+    d.close();
+  }
 }
Index: lucene/src/java/org/apache/lucene/index/DirectoryReader.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/DirectoryReader.java	(revision 1183650)
+++ lucene/src/java/org/apache/lucene/index/DirectoryReader.java	(working copy)
@@ -406,8 +406,15 @@
     return doOpenIfChanged(true, commit);
   }
 
-  // NOTE: always returns a non-null result (ie new reader)
-  // but that could change someday
+  @Override
+  protected final IndexReader doOpenIfChanged(IndexWriter writer, boolean applyAllDeletes) throws CorruptIndexException, IOException {
+    if (writer == this.writer && applyAllDeletes == this.applyAllDeletes) {
+      return doOpenIfChanged();
+    } else {    
+      return super.doOpenIfChanged(writer, applyAllDeletes);
+    }
+  }
+
   private final IndexReader doOpenFromWriter(boolean openReadOnly, IndexCommit commit) throws CorruptIndexException, IOException {
     assert readOnly;
 
@@ -419,10 +426,18 @@
       throw new IllegalArgumentException("a reader obtained from IndexWriter.getReader() cannot currently accept a commit");
     }
 
-    // TODO: right now we *always* make a new reader; in
-    // the future we could have write make some effort to
-    // detect that no changes have occurred
+    if (writer.nrtIsCurrent(segmentInfos)) {
+      return null;
+    }
+
     IndexReader reader = writer.getReader(applyAllDeletes);
+
+    // If in fact no changes took place, return null:
+    if (reader.getVersion() == getVersion()) {
+      reader.decRef();
+      return null;
+    }
+
     reader.readerFinishedListeners = readerFinishedListeners;
     return reader;
   }
Index: lucene/src/java/org/apache/lucene/index/IndexReader.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexReader.java	(revision 1183650)
+++ lucene/src/java/org/apache/lucene/index/IndexReader.java	(working copy)
@@ -561,10 +561,6 @@
    * with the old reader uses "copy on write" semantics to
    * ensure the changes are not seen by other readers.
    *
-   * <p><b>NOTE</b>: If the provided reader is a near real-time
-   * reader, this method will return another near-real-time
-   * reader.
-   * 
    * @throws CorruptIndexException if the index is corrupt
    * @throws IOException if there is a low-level IO error
    * @return null if there are no changes; else, a new
Index: lucene/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1183650)
+++ lucene/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -4073,6 +4073,7 @@
 
   synchronized boolean nrtIsCurrent(SegmentInfos infos) {
     //System.out.println("IW.nrtIsCurrent " + (infos.version == segmentInfos.version && !docWriter.anyChanges() && !bufferedDeletesStream.any()));
+    ensureOpen();
     return infos.version == segmentInfos.version && !docWriter.anyChanges() && !bufferedDeletesStream.any();
   }
 
Index: lucene/src/test-framework/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java
===================================================================
--- lucene/src/test-framework/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java	(revision 1183650)
+++ lucene/src/test-framework/org/apache/lucene/index/ThreadedIndexingAndSearchingTestCase.java	(working copy)
@@ -55,7 +55,7 @@
 
 // TODO
 //   - mix in optimize, addIndexes
-//   - randomoly mix in non-congruent docs
+//   - randomly mix in non-congruent docs
 
 /** Utility class that spawns multiple indexing and
  *  searching threads. */