/**
	 * Expunges the deleted documents.
	 * Compacts and merges all segments containing deleted documents.
	 * @throws IOException
	 */
	public final void expungeDeleted() throws IOException {
		final Vector segmentsToDelete = new Vector();
		final SegmentInfos newInfos = new SegmentInfos();

		if (infoStream != null) {
			infoStream.print("Expunging deleted documents.");
		}
		
		// iterate thru all the segment infos
		for (int i = 0; i < segmentInfos.size(); i++) {
			SegmentInfo si = segmentInfos.info(i);

			Directory directory = si.dir;

			if (SegmentReader.hasDeletions(si)) { // found a deletion

				// make a new segment and merge itself
				String newSegment = newSegmentName();

				SegmentReader reader = SegmentReader.get(si);
				SegmentMerger merger = new SegmentMerger(directory, newSegment);
				merger.add(reader);
				int newDocCount = merger.merge();
				merger.closeReaders();

				// do the compound file thing
				if (useCompoundFile) {
					final Vector filesToDelete = merger
							.createCompoundFile(newSegment + ".tmp");
					synchronized (directory) { // in- & inter-process sync

						boolean locked = false;
						Lock lock = directory.makeLock(COMMIT_LOCK_NAME);
						try {
							locked = lock.obtain(COMMIT_LOCK_TIMEOUT);
							//      make compound file visible for SegmentReaders
							directory.renameFile(newSegment + ".tmp",
									newSegment + ".cfs");
							// delete now unused files of segment
							deleteFiles(filesToDelete);
						} finally {
							if (locked)
								lock.release();
						}
					}
				}

				if ((reader.directory() == this.directory) || // if we own the
															  // directory
						(reader.directory() == this.ramDirectory)) {
					segmentsToDelete.add(reader);
				}

				newInfos
						.add(new SegmentInfo(newSegment, newDocCount, directory));
			} else {
				newInfos.add(si);
			}
		}

		// rewrite the segment info if there is something changed
		if (segmentsToDelete.size() > 0) {
			synchronized (directory) { // in- & inter-process sync
				new Lock.With(directory.makeLock(COMMIT_LOCK_NAME),
						COMMIT_LOCK_TIMEOUT) {
					public Object doBody() throws IOException {
						newInfos.write(directory); // commit before deleting
						deleteSegments(segmentsToDelete); // delete now-unused
														  // segments
						return null;
					}
				}.run();
			}
		}
	}