X-Git-Url: https://git.mdrn.pl/pylucene.git/blobdiff_plain/a2e61f0c04805cfcb8706176758d1283c7e3a55c..aaeed5504b982cf3545252ab528713250aa33eed:/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/index/DirectoryReader.java?ds=sidebyside

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/index/DirectoryReader.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/index/DirectoryReader.java
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@@ -0,0 +1,1359 @@
+package org.apache.lucene.index;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.FieldSelector;
+import org.apache.lucene.search.Similarity;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.Lock;
+import org.apache.lucene.store.LockObtainFailedException;
+import org.apache.lucene.util.MapBackedSet;
+
+/** 
+ * An IndexReader which reads indexes with multiple segments.
+ */
+class DirectoryReader extends IndexReader implements Cloneable {
+  protected Directory directory;
+  protected boolean readOnly;
+
+  IndexWriter writer;
+
+  private IndexDeletionPolicy deletionPolicy;
+  private Lock writeLock;
+  private final SegmentInfos segmentInfos;
+  private boolean stale;
+  private final int termInfosIndexDivisor;
+
+  private boolean rollbackHasChanges;
+
+  private SegmentReader[] subReaders;
+  private int[] starts;                           // 1st docno for each segment
+  private Map<String,byte[]> normsCache = new HashMap<String,byte[]>();
+  private int maxDoc = 0;
+  private int numDocs = -1;
+  private boolean hasDeletions = false;
+
+  // Max version in index as of when we opened; this can be
+  // > our current segmentInfos version in case we were
+  // opened on a past IndexCommit:
+  private long maxIndexVersion;
+
+  private final boolean applyAllDeletes;
+
+  static IndexReader open(final Directory directory, final IndexDeletionPolicy deletionPolicy, final IndexCommit commit, final boolean readOnly,
+                          final int termInfosIndexDivisor) throws CorruptIndexException, IOException {
+    return (IndexReader) new SegmentInfos.FindSegmentsFile(directory) {
+      @Override
+      protected Object doBody(String segmentFileName) throws CorruptIndexException, IOException {
+        SegmentInfos infos = new SegmentInfos();
+        infos.read(directory, segmentFileName);
+        if (readOnly)
+          return new ReadOnlyDirectoryReader(directory, infos, deletionPolicy, termInfosIndexDivisor, null);
+        else
+          return new DirectoryReader(directory, infos, deletionPolicy, false, termInfosIndexDivisor, null);
+      }
+    }.run(commit);
+  }
+
+  /** Construct reading the named set of readers. */
+  DirectoryReader(Directory directory, SegmentInfos sis, IndexDeletionPolicy deletionPolicy, boolean readOnly, int termInfosIndexDivisor,
+                  Collection<ReaderFinishedListener> readerFinishedListeners) throws IOException {
+    this.directory = directory;
+    this.readOnly = readOnly;
+    this.segmentInfos = sis;
+    this.deletionPolicy = deletionPolicy;
+    this.termInfosIndexDivisor = termInfosIndexDivisor;
+
+    if (readerFinishedListeners == null) {
+      this.readerFinishedListeners = new MapBackedSet<ReaderFinishedListener>(new ConcurrentHashMap<ReaderFinishedListener,Boolean>());
+    } else {
+      this.readerFinishedListeners = readerFinishedListeners;
+    }
+    applyAllDeletes = false;
+
+    // To reduce the chance of hitting FileNotFound
+    // (and having to retry), we open segments in
+    // reverse because IndexWriter merges & deletes
+    // the newest segments first.
+
+    SegmentReader[] readers = new SegmentReader[sis.size()];
+    for (int i = sis.size()-1; i >= 0; i--) {
+      boolean success = false;
+      try {
+        readers[i] = SegmentReader.get(readOnly, sis.info(i), termInfosIndexDivisor);
+        readers[i].readerFinishedListeners = this.readerFinishedListeners;
+        success = true;
+      } finally {
+        if (!success) {
+          // Close all readers we had opened:
+          for(i++;i<sis.size();i++) {
+            try {
+              readers[i].close();
+            } catch (Throwable ignore) {
+              // keep going - we want to clean up as much as possible
+            }
+          }
+        }
+      }
+    }
+
+    initialize(readers);
+  }
+
+  // Used by near real-time search
+  DirectoryReader(IndexWriter writer, SegmentInfos infos, int termInfosIndexDivisor, boolean applyAllDeletes) throws IOException {
+    this.directory = writer.getDirectory();
+    this.readOnly = true;
+    this.applyAllDeletes = applyAllDeletes;       // saved for reopen
+
+    this.termInfosIndexDivisor = termInfosIndexDivisor;
+    readerFinishedListeners = writer.getReaderFinishedListeners();
+
+    // IndexWriter synchronizes externally before calling
+    // us, which ensures infos will not change; so there's
+    // no need to process segments in reverse order
+    final int numSegments = infos.size();
+
+    List<SegmentReader> readers = new ArrayList<SegmentReader>();
+    final Directory dir = writer.getDirectory();
+
+    segmentInfos = (SegmentInfos) infos.clone();
+    int infosUpto = 0;
+    for (int i=0;i<numSegments;i++) {
+      boolean success = false;
+      try {
+        final SegmentInfo info = infos.info(i);
+        assert info.dir == dir;
+        final SegmentReader reader = writer.readerPool.getReadOnlyClone(info, true, termInfosIndexDivisor);
+        if (reader.numDocs() > 0 || writer.getKeepFullyDeletedSegments()) {
+          reader.readerFinishedListeners = readerFinishedListeners;
+          readers.add(reader);
+          infosUpto++;
+        } else {
+          reader.close();
+          segmentInfos.remove(infosUpto);
+        }
+        success = true;
+      } finally {
+        if (!success) {
+          // Close all readers we had opened:
+          for(SegmentReader reader : readers) {
+            try {
+              reader.close();
+            } catch (Throwable ignore) {
+              // keep going - we want to clean up as much as possible
+            }
+          }
+        }
+      }
+    }
+
+    this.writer = writer;
+
+    initialize(readers.toArray(new SegmentReader[readers.size()]));
+  }
+
+  /** This constructor is only used for {@link #doOpenIfChanged()} */
+  DirectoryReader(Directory directory, SegmentInfos infos, SegmentReader[] oldReaders, int[] oldStarts,
+                  Map<String,byte[]> oldNormsCache, boolean readOnly, boolean doClone, int termInfosIndexDivisor,
+                  Collection<ReaderFinishedListener> readerFinishedListeners) throws IOException {
+    this.directory = directory;
+    this.readOnly = readOnly;
+    this.segmentInfos = infos;
+    this.termInfosIndexDivisor = termInfosIndexDivisor;
+    assert readerFinishedListeners != null;
+    this.readerFinishedListeners = readerFinishedListeners;
+    applyAllDeletes = false;
+
+    // we put the old SegmentReaders in a map, that allows us
+    // to lookup a reader using its segment name
+    Map<String,Integer> segmentReaders = new HashMap<String,Integer>();
+
+    if (oldReaders != null) {
+      // create a Map SegmentName->SegmentReader
+      for (int i = 0; i < oldReaders.length; i++) {
+        segmentReaders.put(oldReaders[i].getSegmentName(), Integer.valueOf(i));
+      }
+    }
+    
+    SegmentReader[] newReaders = new SegmentReader[infos.size()];
+    
+    // remember which readers are shared between the old and the re-opened
+    // DirectoryReader - we have to incRef those readers
+    boolean[] readerShared = new boolean[infos.size()];
+    
+    for (int i = infos.size() - 1; i>=0; i--) {
+      // find SegmentReader for this segment
+      Integer oldReaderIndex = segmentReaders.get(infos.info(i).name);
+      if (oldReaderIndex == null) {
+        // this is a new segment, no old SegmentReader can be reused
+        newReaders[i] = null;
+      } else {
+        // there is an old reader for this segment - we'll try to reopen it
+        newReaders[i] = oldReaders[oldReaderIndex.intValue()];
+      }
+
+      boolean success = false;
+      try {
+        SegmentReader newReader;
+        if (newReaders[i] == null || infos.info(i).getUseCompoundFile() != newReaders[i].getSegmentInfo().getUseCompoundFile()) {
+
+          // We should never see a totally new segment during cloning
+          assert !doClone;
+
+          // this is a new reader; in case we hit an exception we can close it safely
+          newReader = SegmentReader.get(readOnly, infos.info(i), termInfosIndexDivisor);
+          newReader.readerFinishedListeners = readerFinishedListeners;
+          readerShared[i] = false;
+          newReaders[i] = newReader;
+        } else {
+          newReader = newReaders[i].reopenSegment(infos.info(i), doClone, readOnly);
+          if (newReader == null) {
+            // this reader will be shared between the old and the new one,
+            // so we must incRef it
+            readerShared[i] = true;
+            newReaders[i].incRef();
+          } else {
+            assert newReader.readerFinishedListeners == readerFinishedListeners;
+            readerShared[i] = false;
+            // Steal ref returned to us by reopenSegment:
+            newReaders[i] = newReader;
+          }
+        }
+        success = true;
+      } finally {
+        if (!success) {
+          for (i++; i < infos.size(); i++) {
+            if (newReaders[i] != null) {
+              try {
+                if (!readerShared[i]) {
+                  // this is a new subReader that is not used by the old one,
+                  // we can close it
+                  newReaders[i].close();
+                } else {
+                  // this subReader is also used by the old reader, so instead
+                  // closing we must decRef it
+                  newReaders[i].decRef();
+                }
+              } catch (IOException ignore) {
+                // keep going - we want to clean up as much as possible
+              }
+            }
+          }
+        }
+      }
+    }    
+    
+    // initialize the readers to calculate maxDoc before we try to reuse the old normsCache
+    initialize(newReaders);
+    
+    // try to copy unchanged norms from the old normsCache to the new one
+    if (oldNormsCache != null) {
+      for (Map.Entry<String,byte[]> entry: oldNormsCache.entrySet()) {
+        String field = entry.getKey();
+        if (!hasNorms(field)) {
+          continue;
+        }
+
+        byte[] oldBytes = entry.getValue();
+
+        byte[] bytes = new byte[maxDoc()];
+
+        for (int i = 0; i < subReaders.length; i++) {
+          Integer oldReaderIndex = segmentReaders.get(subReaders[i].getSegmentName());
+
+          // this SegmentReader was not re-opened, we can copy all of its norms 
+          if (oldReaderIndex != null &&
+               (oldReaders[oldReaderIndex.intValue()] == subReaders[i] 
+                 || oldReaders[oldReaderIndex.intValue()].norms.get(field) == subReaders[i].norms.get(field))) {
+            // we don't have to synchronize here: either this constructor is called from a SegmentReader,
+            // in which case no old norms cache is present, or it is called from MultiReader.reopen(),
+            // which is synchronized
+            System.arraycopy(oldBytes, oldStarts[oldReaderIndex.intValue()], bytes, starts[i], starts[i+1] - starts[i]);
+          } else {
+            subReaders[i].norms(field, bytes, starts[i]);
+          }
+        }
+
+        normsCache.put(field, bytes);      // update cache
+      }
+    }
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public String toString() {
+    final StringBuilder buffer = new StringBuilder();
+    if (hasChanges) {
+      buffer.append("*");
+    }
+    buffer.append(getClass().getSimpleName());
+    buffer.append('(');
+    final String segmentsFile = segmentInfos.getCurrentSegmentFileName();
+    if (segmentsFile != null) {
+      buffer.append(segmentsFile);
+    }
+    if (writer != null) {
+      buffer.append(":nrt");
+    }
+    for(int i=0;i<subReaders.length;i++) {
+      buffer.append(' ');
+      buffer.append(subReaders[i]);
+    }
+    buffer.append(')');
+    return buffer.toString();
+  }
+
+  private void initialize(SegmentReader[] subReaders) throws IOException {
+    this.subReaders = subReaders;
+    starts = new int[subReaders.length + 1];    // build starts array
+    for (int i = 0; i < subReaders.length; i++) {
+      starts[i] = maxDoc;
+      maxDoc += subReaders[i].maxDoc();      // compute maxDocs
+
+      if (subReaders[i].hasDeletions())
+        hasDeletions = true;
+    }
+    starts[subReaders.length] = maxDoc;
+
+    if (!readOnly) {
+      maxIndexVersion = SegmentInfos.readCurrentVersion(directory);
+    }
+  }
+
+  @Override
+  public final synchronized Object clone() {
+    try {
+      return clone(readOnly); // Preserve current readOnly
+    } catch (Exception ex) {
+      throw new RuntimeException(ex);
+    }
+  }
+
+  @Override
+  public final synchronized IndexReader clone(boolean openReadOnly) throws CorruptIndexException, IOException {
+    // doOpenIfChanged calls ensureOpen
+    DirectoryReader newReader = doOpenIfChanged((SegmentInfos) segmentInfos.clone(), true, openReadOnly);
+
+    if (this != newReader) {
+      newReader.deletionPolicy = deletionPolicy;
+    }
+    newReader.writer = writer;
+    // If we're cloning a non-readOnly reader, move the
+    // writeLock (if there is one) to the new reader:
+    if (!openReadOnly && writeLock != null) {
+      // In near real-time search, reader is always readonly
+      assert writer == null;
+      newReader.writeLock = writeLock;
+      newReader.hasChanges = hasChanges;
+      newReader.hasDeletions = hasDeletions;
+      writeLock = null;
+      hasChanges = false;
+    }
+    assert newReader.readerFinishedListeners != null;
+
+    return newReader;
+  }
+
+  @Override
+  protected final IndexReader doOpenIfChanged() throws CorruptIndexException, IOException {
+    // Preserve current readOnly
+    return doOpenIfChanged(readOnly, null);
+  }
+
+  @Override
+  protected final IndexReader doOpenIfChanged(boolean openReadOnly) throws CorruptIndexException, IOException {
+    return doOpenIfChanged(openReadOnly, null);
+  }
+
+  @Override
+  protected final IndexReader doOpenIfChanged(final IndexCommit commit) throws CorruptIndexException, IOException {
+    return doOpenIfChanged(true, commit);
+  }
+
+  @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;
+
+    if (!openReadOnly) {
+      throw new IllegalArgumentException("a reader obtained from IndexWriter.getReader() can only be reopened with openReadOnly=true (got false)");
+    }
+
+    if (commit != null) {
+      throw new IllegalArgumentException("a reader obtained from IndexWriter.getReader() cannot currently accept a commit");
+    }
+
+    if (writer.nrtIsCurrent(segmentInfos)) {
+      return null;
+    }
+
+    IndexReader reader = writer.getReader(applyAllDeletes);
+
+    // If in fact no changes took place, return null:
+    if (reader.getVersion() == segmentInfos.getVersion()) {
+      reader.decRef();
+      return null;
+    }
+
+    reader.readerFinishedListeners = readerFinishedListeners;
+    return reader;
+  }
+
+  private IndexReader doOpenIfChanged(final boolean openReadOnly, IndexCommit commit) throws CorruptIndexException, IOException {
+    ensureOpen();
+
+    assert commit == null || openReadOnly;
+
+    // If we were obtained by writer.getReader(), re-ask the
+    // writer to get a new reader.
+    if (writer != null) {
+      return doOpenFromWriter(openReadOnly, commit);
+    } else {
+      return doOpenNoWriter(openReadOnly, commit);
+    }
+  }
+
+  private synchronized IndexReader doOpenNoWriter(final boolean openReadOnly, IndexCommit commit) throws CorruptIndexException, IOException {
+
+    if (commit == null) {
+      if (hasChanges) {
+        // We have changes, which means we are not readOnly:
+        assert readOnly == false;
+        // and we hold the write lock:
+        assert writeLock != null;
+        // so no other writer holds the write lock, which
+        // means no changes could have been done to the index:
+        assert isCurrent();
+
+        if (openReadOnly) {
+          return clone(openReadOnly);
+        } else {
+          return null;
+        }
+      } else if (isCurrent()) {
+        if (openReadOnly != readOnly) {
+          // Just fallback to clone
+          return clone(openReadOnly);
+        } else {
+          return null;
+        }
+      }
+    } else {
+      if (directory != commit.getDirectory()) {
+        throw new IOException("the specified commit does not match the specified Directory");
+      }
+      if (segmentInfos != null && commit.getSegmentsFileName().equals(segmentInfos.getCurrentSegmentFileName())) {
+        if (readOnly != openReadOnly) {
+          // Just fallback to clone
+          return clone(openReadOnly);
+        } else {
+          return null;
+        }
+      }
+    }
+
+    return (IndexReader) new SegmentInfos.FindSegmentsFile(directory) {
+      @Override
+      protected Object doBody(String segmentFileName) throws CorruptIndexException, IOException {
+        SegmentInfos infos = new SegmentInfos();
+        infos.read(directory, segmentFileName);
+        return doOpenIfChanged(infos, false, openReadOnly);
+      }
+    }.run(commit);
+  }
+
+  private synchronized DirectoryReader doOpenIfChanged(SegmentInfos infos, boolean doClone, boolean openReadOnly) throws CorruptIndexException, IOException {
+    DirectoryReader reader;
+    if (openReadOnly) {
+      reader = new ReadOnlyDirectoryReader(directory, infos, subReaders, starts, normsCache, doClone, termInfosIndexDivisor, readerFinishedListeners);
+    } else {
+      reader = new DirectoryReader(directory, infos, subReaders, starts, normsCache, false, doClone, termInfosIndexDivisor, readerFinishedListeners);
+    }
+    return reader;
+  }
+
+  /** Version number when this IndexReader was opened. */
+  @Override
+  public long getVersion() {
+    ensureOpen();
+    return segmentInfos.getVersion();
+  }
+
+  @Override
+  public TermFreqVector[] getTermFreqVectors(int n) throws IOException {
+    ensureOpen();
+    int i = readerIndex(n);        // find segment num
+    return subReaders[i].getTermFreqVectors(n - starts[i]); // dispatch to segment
+  }
+
+  @Override
+  public TermFreqVector getTermFreqVector(int n, String field)
+      throws IOException {
+    ensureOpen();
+    int i = readerIndex(n);        // find segment num
+    return subReaders[i].getTermFreqVector(n - starts[i], field);
+  }
+
+
+  @Override
+  public void getTermFreqVector(int docNumber, String field, TermVectorMapper mapper) throws IOException {
+    ensureOpen();
+    int i = readerIndex(docNumber);        // find segment num
+    subReaders[i].getTermFreqVector(docNumber - starts[i], field, mapper);
+  }
+
+  @Override
+  public void getTermFreqVector(int docNumber, TermVectorMapper mapper) throws IOException {
+    ensureOpen();
+    int i = readerIndex(docNumber);        // find segment num
+    subReaders[i].getTermFreqVector(docNumber - starts[i], mapper);
+  }
+
+  @Deprecated
+  @Override
+  public boolean isOptimized() {
+    ensureOpen();
+    return segmentInfos.size() == 1 && !hasDeletions();
+  }
+
+  @Override
+  public int numDocs() {
+    // Don't call ensureOpen() here (it could affect performance)
+
+    // NOTE: multiple threads may wind up init'ing
+    // numDocs... but that's harmless
+    if (numDocs == -1) {        // check cache
+      int n = 0;                // cache miss--recompute
+      for (int i = 0; i < subReaders.length; i++)
+        n += subReaders[i].numDocs();      // sum from readers
+      numDocs = n;
+    }
+    return numDocs;
+  }
+
+  @Override
+  public int maxDoc() {
+    // Don't call ensureOpen() here (it could affect performance)
+    return maxDoc;
+  }
+
+  // inherit javadoc
+  @Override
+  public Document document(int n, FieldSelector fieldSelector) throws CorruptIndexException, IOException {
+    ensureOpen();
+    int i = readerIndex(n);                          // find segment num
+    return subReaders[i].document(n - starts[i], fieldSelector);    // dispatch to segment reader
+  }
+
+  @Override
+  public boolean isDeleted(int n) {
+    // Don't call ensureOpen() here (it could affect performance)
+    final int i = readerIndex(n);                           // find segment num
+    return subReaders[i].isDeleted(n - starts[i]);    // dispatch to segment reader
+  }
+
+  @Override
+  public boolean hasDeletions() {
+    ensureOpen();
+    return hasDeletions;
+  }
+
+  @Override
+  protected void doDelete(int n) throws CorruptIndexException, IOException {
+    numDocs = -1;                             // invalidate cache
+    int i = readerIndex(n);                   // find segment num
+    subReaders[i].deleteDocument(n - starts[i]);      // dispatch to segment reader
+    hasDeletions = true;
+  }
+
+  @Override
+  protected void doUndeleteAll() throws CorruptIndexException, IOException {
+    for (int i = 0; i < subReaders.length; i++)
+      subReaders[i].undeleteAll();
+
+    hasDeletions = false;
+    numDocs = -1;                                 // invalidate cache
+  }
+
+  private int readerIndex(int n) {    // find reader for doc n:
+    return readerIndex(n, this.starts, this.subReaders.length);
+  }
+  
+  final static int readerIndex(int n, int[] starts, int numSubReaders) {    // find reader for doc n:
+    int lo = 0;                                      // search starts array
+    int hi = numSubReaders - 1;                  // for first element less
+
+    while (hi >= lo) {
+      int mid = (lo + hi) >>> 1;
+      int midValue = starts[mid];
+      if (n < midValue)
+        hi = mid - 1;
+      else if (n > midValue)
+        lo = mid + 1;
+      else {                                      // found a match
+        while (mid+1 < numSubReaders && starts[mid+1] == midValue) {
+          mid++;                                  // scan to last match
+        }
+        return mid;
+      }
+    }
+    return hi;
+  }
+
+  @Override
+  public boolean hasNorms(String field) throws IOException {
+    ensureOpen();
+    for (int i = 0; i < subReaders.length; i++) {
+      if (subReaders[i].hasNorms(field)) return true;
+    }
+    return false;
+  }
+
+  @Override
+  public synchronized byte[] norms(String field) throws IOException {
+    ensureOpen();
+    byte[] bytes = normsCache.get(field);
+    if (bytes != null)
+      return bytes;          // cache hit
+    if (!hasNorms(field))
+      return null;
+
+    bytes = new byte[maxDoc()];
+    for (int i = 0; i < subReaders.length; i++)
+      subReaders[i].norms(field, bytes, starts[i]);
+    normsCache.put(field, bytes);      // update cache
+    return bytes;
+  }
+
+  @Override
+  public synchronized void norms(String field, byte[] result, int offset)
+    throws IOException {
+    ensureOpen();
+    byte[] bytes = normsCache.get(field);
+    if (bytes==null && !hasNorms(field)) {
+      Arrays.fill(result, offset, result.length, Similarity.getDefault().encodeNormValue(1.0f));
+    } else if (bytes != null) {                           // cache hit
+      System.arraycopy(bytes, 0, result, offset, maxDoc());
+    } else {
+      for (int i = 0; i < subReaders.length; i++) {      // read from segments
+        subReaders[i].norms(field, result, offset + starts[i]);
+      }
+    }
+  }
+
+  @Override
+  protected void doSetNorm(int n, String field, byte value)
+    throws CorruptIndexException, IOException {
+    synchronized (normsCache) {
+      normsCache.remove(field);                         // clear cache      
+    }
+    int i = readerIndex(n);                           // find segment num
+    subReaders[i].setNorm(n-starts[i], field, value); // dispatch
+  }
+
+  @Override
+  public TermEnum terms() throws IOException {
+    ensureOpen();
+    if (subReaders.length == 1) {
+      // Optimize single segment case:
+      return subReaders[0].terms();
+    } else {
+      return new MultiTermEnum(this, subReaders, starts, null);
+    }
+  }
+
+  @Override
+  public TermEnum terms(Term term) throws IOException {
+    ensureOpen();
+    if (subReaders.length == 1) {
+      // Optimize single segment case:
+      return subReaders[0].terms(term);
+    } else {
+      return new MultiTermEnum(this, subReaders, starts, term);
+    }
+  }
+
+  @Override
+  public int docFreq(Term t) throws IOException {
+    ensureOpen();
+    int total = 0;          // sum freqs in segments
+    for (int i = 0; i < subReaders.length; i++)
+      total += subReaders[i].docFreq(t);
+    return total;
+  }
+
+  @Override
+  public TermDocs termDocs() throws IOException {
+    ensureOpen();
+    if (subReaders.length == 1) {
+      // Optimize single segment case:
+      return subReaders[0].termDocs();
+    } else {
+      return new MultiTermDocs(this, subReaders, starts);
+    }
+  }
+
+  @Override
+  public TermDocs termDocs(Term term) throws IOException {
+    ensureOpen();
+    if (subReaders.length == 1) {
+      // Optimize single segment case:
+      return subReaders[0].termDocs(term);
+    } else {
+      return super.termDocs(term);
+    }
+  }
+
+  @Override
+  public TermPositions termPositions() throws IOException {
+    ensureOpen();
+    if (subReaders.length == 1) {
+      // Optimize single segment case:
+      return subReaders[0].termPositions();
+    } else {
+      return new MultiTermPositions(this, subReaders, starts);
+    }
+  }
+
+  /**
+   * Tries to acquire the WriteLock on this directory. this method is only valid if this IndexReader is directory
+   * owner.
+   *
+   * @throws StaleReaderException  if the index has changed since this reader was opened
+   * @throws CorruptIndexException if the index is corrupt
+   * @throws org.apache.lucene.store.LockObtainFailedException
+   *                               if another writer has this index open (<code>write.lock</code> could not be
+   *                               obtained)
+   * @throws IOException           if there is a low-level IO error
+   */
+  @Override
+  protected void acquireWriteLock() throws StaleReaderException, CorruptIndexException, LockObtainFailedException, IOException {
+
+    if (readOnly) {
+      // NOTE: we should not reach this code w/ the core
+      // IndexReader classes; however, an external subclass
+      // of IndexReader could reach this.
+      ReadOnlySegmentReader.noWrite();
+    }
+
+    if (segmentInfos != null) {
+      ensureOpen();
+      if (stale)
+        throw new StaleReaderException("IndexReader out of date and no longer valid for delete, undelete, or setNorm operations");
+
+      if (writeLock == null) {
+        Lock writeLock = directory.makeLock(IndexWriter.WRITE_LOCK_NAME);
+        if (!writeLock.obtain(IndexWriterConfig.WRITE_LOCK_TIMEOUT)) // obtain write lock
+          throw new LockObtainFailedException("Index locked for write: " + writeLock);
+        this.writeLock = writeLock;
+
+        // we have to check whether index has changed since this reader was opened.
+        // if so, this reader is no longer valid for
+        // deletion
+        if (SegmentInfos.readCurrentVersion(directory) > maxIndexVersion) {
+          stale = true;
+          this.writeLock.release();
+          this.writeLock = null;
+          throw new StaleReaderException("IndexReader out of date and no longer valid for delete, undelete, or setNorm operations");
+        }
+      }
+    }
+  }
+
+  /**
+   * Commit changes resulting from delete, undeleteAll, or setNorm operations
+   * <p/>
+   * If an exception is hit, then either no changes or all changes will have been committed to the index (transactional
+   * semantics).
+   *
+   * @throws IOException if there is a low-level IO error
+   */
+  @Override
+  protected void doCommit(Map<String,String> commitUserData) throws IOException {
+    if (hasChanges) {
+      segmentInfos.setUserData(commitUserData);
+      // Default deleter (for backwards compatibility) is
+      // KeepOnlyLastCommitDeleter:
+      IndexFileDeleter deleter = new IndexFileDeleter(directory,
+                                                      deletionPolicy == null ? new KeepOnlyLastCommitDeletionPolicy() : deletionPolicy,
+                                                      segmentInfos, null, null);
+      segmentInfos.updateGeneration(deleter.getLastSegmentInfos());
+      segmentInfos.changed();
+
+      // Checkpoint the state we are about to change, in
+      // case we have to roll back:
+      startCommit();
+
+      final List<SegmentInfo> rollbackSegments = segmentInfos.createBackupSegmentInfos(false);
+
+      boolean success = false;
+      try {
+        for (int i = 0; i < subReaders.length; i++)
+          subReaders[i].commit();
+
+        // Remove segments that contain only 100% deleted
+        // docs:
+        segmentInfos.pruneDeletedSegments();
+
+        // Sync all files we just wrote
+        directory.sync(segmentInfos.files(directory, false));
+        segmentInfos.commit(directory);
+        success = true;
+      } finally {
+
+        if (!success) {
+
+          // Rollback changes that were made to
+          // SegmentInfos but failed to get [fully]
+          // committed.  This way this reader instance
+          // remains consistent (matched to what's
+          // actually in the index):
+          rollbackCommit();
+
+          // Recompute deletable files & remove them (so
+          // partially written .del files, etc, are
+          // removed):
+          deleter.refresh();
+
+          // Restore all SegmentInfos (in case we pruned some)
+          segmentInfos.rollbackSegmentInfos(rollbackSegments);
+        }
+      }
+
+      // Have the deleter remove any now unreferenced
+      // files due to this commit:
+      deleter.checkpoint(segmentInfos, true);
+      deleter.close();
+
+      maxIndexVersion = segmentInfos.getVersion();
+
+      if (writeLock != null) {
+        writeLock.release();  // release write lock
+        writeLock = null;
+      }
+    }
+    hasChanges = false;
+  }
+
+  void startCommit() {
+    rollbackHasChanges = hasChanges;
+    for (int i = 0; i < subReaders.length; i++) {
+      subReaders[i].startCommit();
+    }
+  }
+
+  void rollbackCommit() {
+    hasChanges = rollbackHasChanges;
+    for (int i = 0; i < subReaders.length; i++) {
+      subReaders[i].rollbackCommit();
+    }
+  }
+
+  @Override
+  public Map<String,String> getCommitUserData() {
+    ensureOpen();
+    return segmentInfos.getUserData();
+  }
+
+  @Override
+  public boolean isCurrent() throws CorruptIndexException, IOException {
+    ensureOpen();
+    if (writer == null || writer.isClosed()) {
+      // we loaded SegmentInfos from the directory
+      return SegmentInfos.readCurrentVersion(directory) == segmentInfos.getVersion();
+    } else {
+      return writer.nrtIsCurrent(segmentInfos);
+    }
+  }
+
+  @Override
+  protected synchronized void doClose() throws IOException {
+    IOException ioe = null;
+    normsCache = null;
+    for (int i = 0; i < subReaders.length; i++) {
+      // try to close each reader, even if an exception is thrown
+      try {
+        subReaders[i].decRef();
+      } catch (IOException e) {
+        if (ioe == null) ioe = e;
+      }
+    }
+
+    if (writer != null) {
+      // Since we just closed, writer may now be able to
+      // delete unused files:
+      writer.deletePendingFiles();
+    }
+
+    // throw the first exception
+    if (ioe != null) throw ioe;
+  }
+
+  @Override
+  public Collection<String> getFieldNames (IndexReader.FieldOption fieldNames) {
+    ensureOpen();
+    return getFieldNames(fieldNames, this.subReaders);
+  }
+  
+  static Collection<String> getFieldNames (IndexReader.FieldOption fieldNames, IndexReader[] subReaders) {
+    // maintain a unique set of field names
+    Set<String> fieldSet = new HashSet<String>();
+    for (IndexReader reader : subReaders) {
+      Collection<String> names = reader.getFieldNames(fieldNames);
+      fieldSet.addAll(names);
+    }
+    return fieldSet;
+  } 
+  
+  @Override
+  public IndexReader[] getSequentialSubReaders() {
+    return subReaders;
+  }
+
+  /** Returns the directory this index resides in. */
+  @Override
+  public Directory directory() {
+    // Don't ensureOpen here -- in certain cases, when a
+    // cloned/reopened reader needs to commit, it may call
+    // this method on the closed original reader
+    return directory;
+  }
+
+  @Override
+  public int getTermInfosIndexDivisor() {
+    ensureOpen();
+    return termInfosIndexDivisor;
+  }
+
+  /**
+   * Expert: return the IndexCommit that this reader has opened.
+   * <p/>
+   * @lucene.experimental
+   */
+  @Override
+  public IndexCommit getIndexCommit() throws IOException {
+    ensureOpen();
+    return new ReaderCommit(segmentInfos, directory);
+  }
+
+  /** @see org.apache.lucene.index.IndexReader#listCommits */
+  public static Collection<IndexCommit> listCommits(Directory dir) throws IOException {
+    final String[] files = dir.listAll();
+
+    List<IndexCommit> commits = new ArrayList<IndexCommit>();
+
+    SegmentInfos latest = new SegmentInfos();
+    latest.read(dir);
+    final long currentGen = latest.getGeneration();
+
+    commits.add(new ReaderCommit(latest, dir));
+
+    for(int i=0;i<files.length;i++) {
+
+      final String fileName = files[i];
+
+      if (fileName.startsWith(IndexFileNames.SEGMENTS) &&
+          !fileName.equals(IndexFileNames.SEGMENTS_GEN) &&
+          SegmentInfos.generationFromSegmentsFileName(fileName) < currentGen) {
+
+        SegmentInfos sis = new SegmentInfos();
+        try {
+          // IOException allowed to throw there, in case
+          // segments_N is corrupt
+          sis.read(dir, fileName);
+        } catch (FileNotFoundException fnfe) {
+          // LUCENE-948: on NFS (and maybe others), if
+          // you have writers switching back and forth
+          // between machines, it's very likely that the
+          // dir listing will be stale and will claim a
+          // file segments_X exists when in fact it
+          // doesn't.  So, we catch this and handle it
+          // as if the file does not exist
+          sis = null;
+        }
+
+        if (sis != null)
+          commits.add(new ReaderCommit(sis, dir));
+      }
+    }
+
+    // Ensure that the commit points are sorted in ascending order.
+    Collections.sort(commits);
+
+    return commits;
+  }
+
+  private static final class ReaderCommit extends IndexCommit {
+    private String segmentsFileName;
+    Collection<String> files;
+    Directory dir;
+    long generation;
+    long version;
+    final Map<String,String> userData;
+    private final int segmentCount;
+
+    ReaderCommit(SegmentInfos infos, Directory dir) throws IOException {
+      segmentsFileName = infos.getCurrentSegmentFileName();
+      this.dir = dir;
+      userData = infos.getUserData();
+      files = Collections.unmodifiableCollection(infos.files(dir, true));
+      version = infos.getVersion();
+      generation = infos.getGeneration();
+      segmentCount = infos.size();
+    }
+
+    @Override
+    public String toString() {
+      return "DirectoryReader.ReaderCommit(" + segmentsFileName + ")";
+    }
+
+    @Override
+    public int getSegmentCount() {
+      return segmentCount;
+    }
+
+    @Override
+    public String getSegmentsFileName() {
+      return segmentsFileName;
+    }
+
+    @Override
+    public Collection<String> getFileNames() {
+      return files;
+    }
+
+    @Override
+    public Directory getDirectory() {
+      return dir;
+    }
+
+    @Override
+    public long getVersion() {
+      return version;
+    }
+
+    @Override
+    public long getGeneration() {
+      return generation;
+    }
+
+    @Override
+    public boolean isDeleted() {
+      return false;
+    }
+
+    @Override
+    public Map<String,String> getUserData() {
+      return userData;
+    }
+
+    @Override
+    public void delete() {
+      throw new UnsupportedOperationException("This IndexCommit does not support deletions");
+    }
+  }
+
+  static class MultiTermEnum extends TermEnum {
+    IndexReader topReader; // used for matching TermEnum to TermDocs
+    private SegmentMergeQueue queue;
+  
+    private Term term;
+    private int docFreq;
+    final SegmentMergeInfo[] matchingSegments; // null terminated array of matching segments
+
+    public MultiTermEnum(IndexReader topReader, IndexReader[] readers, int[] starts, Term t)
+      throws IOException {
+      this.topReader = topReader;
+      queue = new SegmentMergeQueue(readers.length);
+      matchingSegments = new SegmentMergeInfo[readers.length+1];
+      for (int i = 0; i < readers.length; i++) {
+        IndexReader reader = readers[i];
+        TermEnum termEnum;
+  
+        if (t != null) {
+          termEnum = reader.terms(t);
+        } else
+          termEnum = reader.terms();
+  
+        SegmentMergeInfo smi = new SegmentMergeInfo(starts[i], termEnum, reader);
+        smi.ord = i;
+        if (t == null ? smi.next() : termEnum.term() != null)
+          queue.add(smi);          // initialize queue
+        else
+          smi.close();
+      }
+  
+      if (t != null && queue.size() > 0) {
+        next();
+      }
+    }
+  
+    @Override
+    public boolean next() throws IOException {
+      for (int i=0; i<matchingSegments.length; i++) {
+        SegmentMergeInfo smi = matchingSegments[i];
+        if (smi==null) break;
+        if (smi.next())
+          queue.add(smi);
+        else
+          smi.close(); // done with segment
+      }
+      
+      int numMatchingSegments = 0;
+      matchingSegments[0] = null;
+
+      SegmentMergeInfo top = queue.top();
+
+      if (top == null) {
+        term = null;
+        return false;
+      }
+  
+      term = top.term;
+      docFreq = 0;
+  
+      while (top != null && term.compareTo(top.term) == 0) {
+        matchingSegments[numMatchingSegments++] = top;
+        queue.pop();
+        docFreq += top.termEnum.docFreq();    // increment freq
+        top = queue.top();
+      }
+
+      matchingSegments[numMatchingSegments] = null;
+      return true;
+    }
+  
+    @Override
+    public Term term() {
+      return term;
+    }
+  
+    @Override
+    public int docFreq() {
+      return docFreq;
+    }
+  
+    @Override
+    public void close() throws IOException {
+      queue.close();
+    }
+  }
+
+  static class MultiTermDocs implements TermDocs {
+    IndexReader topReader;  // used for matching TermEnum to TermDocs
+    protected IndexReader[] readers;
+    protected int[] starts;
+    protected Term term;
+  
+    protected int base = 0;
+    protected int pointer = 0;
+  
+    private TermDocs[] readerTermDocs;
+    protected TermDocs current;              // == readerTermDocs[pointer]
+
+    private MultiTermEnum tenum;  // the term enum used for seeking... can be null
+    int matchingSegmentPos;  // position into the matching segments from tenum
+    SegmentMergeInfo smi;     // current segment mere info... can be null
+
+    public MultiTermDocs(IndexReader topReader, IndexReader[] r, int[] s) {
+      this.topReader = topReader;
+      readers = r;
+      starts = s;
+  
+      readerTermDocs = new TermDocs[r.length];
+    }
+
+    public int doc() {
+      return base + current.doc();
+    }
+    public int freq() {
+      return current.freq();
+    }
+  
+    public void seek(Term term) {
+      this.term = term;
+      this.base = 0;
+      this.pointer = 0;
+      this.current = null;
+      this.tenum = null;
+      this.smi = null;
+      this.matchingSegmentPos = 0;
+    }
+  
+    public void seek(TermEnum termEnum) throws IOException {
+      seek(termEnum.term());
+      if (termEnum instanceof MultiTermEnum) {
+        tenum = (MultiTermEnum)termEnum;
+        if (topReader != tenum.topReader)
+          tenum = null;
+      }
+    }
+  
+    public boolean next() throws IOException {
+      for(;;) {
+        if (current!=null && current.next()) {
+          return true;
+        }
+        else if (pointer < readers.length) {
+          if (tenum != null) {
+            smi = tenum.matchingSegments[matchingSegmentPos++];
+            if (smi==null) {
+              pointer = readers.length;
+              return false;
+            }
+            pointer = smi.ord;
+          }
+          base = starts[pointer];
+          current = termDocs(pointer++);
+        } else {
+          return false;
+        }
+      }
+    }
+  
+    /** Optimized implementation. */
+    public int read(final int[] docs, final int[] freqs) throws IOException {
+      while (true) {
+        while (current == null) {
+          if (pointer < readers.length) {      // try next segment
+            if (tenum != null) {
+              smi = tenum.matchingSegments[matchingSegmentPos++];
+              if (smi==null) {
+                pointer = readers.length;
+                return 0;
+              }
+              pointer = smi.ord;
+            }
+            base = starts[pointer];
+            current = termDocs(pointer++);
+          } else {
+            return 0;
+          }
+        }
+        int end = current.read(docs, freqs);
+        if (end == 0) {          // none left in segment
+          current = null;
+        } else {            // got some
+          final int b = base;        // adjust doc numbers
+          for (int i = 0; i < end; i++)
+           docs[i] += b;
+          return end;
+        }
+      }
+    }
+  
+   /* A Possible future optimization could skip entire segments */ 
+    public boolean skipTo(int target) throws IOException {
+      for(;;) {
+        if (current != null && current.skipTo(target-base)) {
+          return true;
+        } else if (pointer < readers.length) {
+          if (tenum != null) {
+            SegmentMergeInfo smi = tenum.matchingSegments[matchingSegmentPos++];
+            if (smi==null) {
+              pointer = readers.length;
+              return false;
+            }
+            pointer = smi.ord;
+          }
+          base = starts[pointer];
+          current = termDocs(pointer++);
+        } else
+          return false;
+      }
+    }
+  
+    private TermDocs termDocs(int i) throws IOException {
+      TermDocs result = readerTermDocs[i];
+      if (result == null)
+        result = readerTermDocs[i] = termDocs(readers[i]);
+      if (smi != null) {
+        assert(smi.ord == i);
+        assert(smi.termEnum.term().equals(term));
+        result.seek(smi.termEnum);
+      } else {
+        result.seek(term);
+      }
+      return result;
+    }
+  
+    protected TermDocs termDocs(IndexReader reader)
+      throws IOException {
+      return term==null ? reader.termDocs(null) : reader.termDocs();
+    }
+  
+    public void close() throws IOException {
+      for (int i = 0; i < readerTermDocs.length; i++) {
+        if (readerTermDocs[i] != null)
+          readerTermDocs[i].close();
+      }
+    }
+  }
+
+  static class MultiTermPositions extends MultiTermDocs implements TermPositions {
+    public MultiTermPositions(IndexReader topReader, IndexReader[] r, int[] s) {
+      super(topReader,r,s);
+    }
+  
+    @Override
+    protected TermDocs termDocs(IndexReader reader) throws IOException {
+      return reader.termPositions();
+    }
+  
+    public int nextPosition() throws IOException {
+      return ((TermPositions)current).nextPosition();
+    }
+    
+    public int getPayloadLength() {
+      return ((TermPositions)current).getPayloadLength();
+    }
+     
+    public byte[] getPayload(byte[] data, int offset) throws IOException {
+      return ((TermPositions)current).getPayload(data, offset);
+    }
+  
+  
+    // TODO: Remove warning after API has been finalized
+    public boolean isPayloadAvailable() {
+      return ((TermPositions) current).isPayloadAvailable();
+    }
+  }
+}