[JGIT PATCH 00/18] Misc. performance tweaks

@@ -251,7 +251,8 @@ public RevObject nextObject() throws MissingObjectException,
 
 			switch (sType) {
 			case Constants.OBJ_BLOB: {
-				final RevObject o = lookupAny(treeWalk.getObjectId(0), sType);
+				treeWalk.getObjectId(idBuffer, 0);
+				final RevObject o = lookupAny(idBuffer, sType);
 				if ((o.flags & SEEN) != 0)
 					continue;
 				o.flags |= SEEN;

@@ -262,7 +263,8 @@ public RevObject nextObject() throws MissingObjectException,
 				return o;
 			}
 			case Constants.OBJ_TREE: {
-				final RevObject o = lookupAny(treeWalk.getObjectId(0), sType);
+				treeWalk.getObjectId(idBuffer, 0);
+				final RevObject o = lookupAny(idBuffer, sType);
 				if ((o.flags & SEEN) != 0)
 					continue;
 				o.flags |= SEEN;

@@ -276,8 +278,9 @@ public RevObject nextObject() throws MissingObjectException,
 			default:
 				if (FileMode.GITLINK.equals(mode))
 					continue;
+				treeWalk.getObjectId(idBuffer, 0);
 				throw new CorruptObjectException("Invalid mode " + mode
-						+ " for " + treeWalk.getObjectId(0).name() + " "
+						+ " for " + idBuffer.name() + " "
 						+ treeWalk.getPathString() + " in " + currentTree + ".");
 			}
 		}

@@ -390,13 +393,13 @@ private void markTreeUninteresting(final RevTree tree)
 
 			switch (sType) {
 			case Constants.OBJ_BLOB: {
-				final ObjectId sid = treeWalk.getObjectId(0);
-				lookupAny(sid, sType).flags |= UNINTERESTING;
+				treeWalk.getObjectId(idBuffer, 0);
+				lookupAny(idBuffer, sType).flags |= UNINTERESTING;
 				continue;
 			}
 			case Constants.OBJ_TREE: {
-				final ObjectId sid = treeWalk.getObjectId(0);
-				final RevObject subtree = lookupAny(sid, sType);
+				treeWalk.getObjectId(idBuffer, 0);
+				final RevObject subtree = lookupAny(idBuffer, sType);
 				if ((subtree.flags & UNINTERESTING) == 0) {
 					subtree.flags |= UNINTERESTING;
 					treeWalk.enterSubtree();

@@ -406,8 +409,9 @@ private void markTreeUninteresting(final RevTree tree)
 			default:
 				if (FileMode.GITLINK.equals(mode))
 					continue;
+				treeWalk.getObjectId(idBuffer, 0);
 				throw new CorruptObjectException("Invalid mode " + mode
-						+ " for " + treeWalk.getObjectId(0).name() + " "
+						+ " for " + idBuffer.name() + " "
 						+ treeWalk.getPathString() + " in " + tree + ".");
 			}
 		}

@@ -66,6 +66,15 @@ MutableObjectId(MutableObjectId src) {
 		this.w5 = src.w5;
 	}
 
+	/** Make this id match {@link ObjectId#zeroId()}. */
+	public void clear() {
+		w1 = 0;
+		w2 = 0;
+		w3 = 0;
+		w4 = 0;
+		w5 = 0;
+	}
+
 	/**
 	 * Convert an ObjectId from raw binary representation.
 	 * 

@@ -55,7 +55,7 @@ public void test003_lookupCompressedObject() throws IOException {
 
 		id = ObjectId.fromString("902d5476fa249b7abc9d84c611577a81381f0327");
 		pr = new PackFile(db, TEST_IDX, TEST_PACK);
-		or = pr.get(id);
+		or = pr.get(new WindowCursor(), id);
 		assertNotNull(or);
 		assertEquals(id, or.getId());
 		assertEquals(Constants.OBJ_TREE, or.getType());

@@ -117,25 +117,6 @@ public boolean hasObject(final AnyObjectId id) {
 	/**
 	 * Get an object from this pack.
 	 * 
-	 * @param id
-	 *            the object to obtain from the pack. Must not be null.
-	 * @return the object loader for the requested object if it is contained in
-	 *         this pack; null if the object was not found.
-	 * @throws IOException
-	 *             the pack file or the index could not be read.
-	 */
-	public PackedObjectLoader get(final AnyObjectId id) throws IOException {
-		final WindowCursor wc = new WindowCursor();
-		try {
-			return get(wc, id);
-		} finally {
-			wc.release();
-		}
-	}
-
-	/**
-	 * Get an object from this pack.
-	 * 
 	 * @param curs
 	 *            temporary working space associated with the calling thread.
 	 * @param id

@@ -51,6 +51,7 @@
 import org.spearce.jgit.errors.IncorrectObjectTypeException;
 import org.spearce.jgit.errors.MissingObjectException;
 import org.spearce.jgit.lib.ObjectId;
+import org.spearce.jgit.lib.WindowCursor;
 import org.spearce.jgit.treewalk.AbstractTreeIterator;
 import org.spearce.jgit.treewalk.CanonicalTreeParser;
 import org.spearce.jgit.treewalk.FileTreeIterator;

@@ -110,8 +111,9 @@ public int parseArguments(final Parameters params) throws CmdLineException {
 			throw new CmdLineException(name + " is not a tree");
 
 		final CanonicalTreeParser p = new CanonicalTreeParser();
+		final WindowCursor curs = new WindowCursor();
 		try {
-			p.reset(clp.getRepository(), clp.getRevWalk().parseTree(id));
+			p.reset(clp.getRepository(), clp.getRevWalk().parseTree(id), curs);
 		} catch (MissingObjectException e) {
 			throw new CmdLineException(name + " is not a tree");
 		} catch (IncorrectObjectTypeException e) {

@@ -119,6 +121,8 @@ public int parseArguments(final Parameters params) throws CmdLineException {
 		} catch (IOException e) {
 			throw new CmdLineException("cannot read " + name + ": "
 					+ e.getMessage());
+		} finally {
+			curs.release();
 		}
 
 		setter.addValue(p);

@@ -45,7 +45,6 @@
 import org.spearce.jgit.lib.AnyObjectId;
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
-import org.spearce.jgit.lib.ObjectId;
 import org.spearce.jgit.lib.Repository;
 import org.spearce.jgit.treewalk.TreeWalk;
 

@@ -296,7 +295,7 @@ public RevObject nextObject() throws MissingObjectException,
 				continue;
 			if (o instanceof RevTree) {
 				currentTree = (RevTree) o;
-				treeWalk.reset(new ObjectId[] { currentTree });
+				treeWalk.reset(currentTree);
 			}
 			return o;
 		}

@@ -386,7 +385,7 @@ private void markTreeUninteresting(final RevTree tree)
 			return;
 		tree.flags |= UNINTERESTING;
 
-		treeWalk.reset(new ObjectId[] { tree });
+		treeWalk.reset(tree);
 		while (treeWalk.next()) {
 			final FileMode mode = treeWalk.getFileMode(0);
 			final int sType = mode.getObjectType();

@@ -296,7 +296,7 @@ private void processBlob(final RevObject obj) throws TransportException {
 
 	private void processTree(final RevObject obj) throws TransportException {
 		try {
-			treeWalk.reset(new ObjectId[] { obj });
+			treeWalk.reset(obj);
 			while (treeWalk.next()) {
 				final FileMode mode = treeWalk.getFileMode(0);
 				final int sType = mode.getObjectType();

@@ -720,7 +720,7 @@ private void markTreeComplete(final RevTree tree) throws IOException {
 		if (tree.has(COMPLETE))
 			return;
 		tree.add(COMPLETE);
-		treeWalk.reset(new ObjectId[] { tree });
+		treeWalk.reset(tree);
 		while (treeWalk.next()) {
 			final FileMode mode = treeWalk.getFileMode(0);
 			final int sType = mode.getObjectType();

@@ -46,8 +46,10 @@
 import org.spearce.jgit.errors.IncorrectObjectTypeException;
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
+import org.spearce.jgit.lib.MutableObjectId;
 import org.spearce.jgit.lib.ObjectId;
 import org.spearce.jgit.lib.Repository;
+import org.spearce.jgit.lib.WindowCursor;
 import org.spearce.jgit.treewalk.filter.TreeFilter;
 
 /**

@@ -347,6 +349,32 @@ public abstract AbstractTreeIterator createSubtreeIterator(Repository repo)
 			throws IncorrectObjectTypeException, IOException;
 
 	/**
+	 * Create a new iterator for the current entry's subtree.
+	 * <p>
+	 * The parent reference of the iterator must be <code>this</code>, otherwise
+	 * the caller would not be able to exit out of the subtree iterator
+	 * correctly and return to continue walking <code>this</code>.
+	 * 
+	 * @param repo
+	 *            repository to load the tree data from.
+	 * @param idBuffer
+	 *            temporary ObjectId buffer for use by this method.
+	 * @param curs
+	 *            window cursor to use during repository access.
+	 * @return a new parser that walks over the current subtree.
+	 * @throws IncorrectObjectTypeException
+	 *             the current entry is not actually a tree and cannot be parsed
+	 *             as though it were a tree.
+	 * @throws IOException
+	 *             a loose object or pack file could not be read.
+	 */
+	public AbstractTreeIterator createSubtreeIterator(final Repository repo,
+			final MutableObjectId idBuffer, final WindowCursor curs)
+			throws IncorrectObjectTypeException, IOException {
+		return createSubtreeIterator(repo);
+	}
+
+	/**
 	 * Is this tree iterator positioned on its first entry?
 	 * <p>
 	 * An iterator is positioned on the first entry if <code>back(1)</code>

@@ -41,11 +41,14 @@
 
 import org.spearce.jgit.errors.IncorrectObjectTypeException;
 import org.spearce.jgit.errors.MissingObjectException;
+import org.spearce.jgit.lib.AnyObjectId;
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
+import org.spearce.jgit.lib.MutableObjectId;
 import org.spearce.jgit.lib.ObjectId;
 import org.spearce.jgit.lib.ObjectLoader;
 import org.spearce.jgit.lib.Repository;
+import org.spearce.jgit.lib.WindowCursor;
 
 /** Parses raw Git trees from the canonical semi-text/semi-binary format. */
 public class CanonicalTreeParser extends AbstractTreeIterator {

@@ -87,6 +90,8 @@ public void reset(final byte[] treeData) {
 	 * @param id
 	 *            identity of the tree being parsed; used only in exception
 	 *            messages if data corruption is found.
+	 * @param curs
+	 *            window cursor to use during repository access.
 	 * @throws MissingObjectException
 	 *             the object supplied is not available from the repository.
 	 * @throws IncorrectObjectTypeException

@@ -95,27 +100,46 @@ public void reset(final byte[] treeData) {
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
-	public void reset(final Repository repo, final ObjectId id)
+	public void reset(final Repository repo, final AnyObjectId id,
+			final WindowCursor curs)
 			throws IncorrectObjectTypeException, IOException {
-		final ObjectLoader ldr = repo.openObject(id);
-		if (ldr == null)
-			throw new MissingObjectException(id, Constants.TYPE_TREE);
+		final ObjectLoader ldr = repo.openObject(curs, id);
+		if (ldr == null) {
+			final ObjectId me = id.toObjectId();
+			throw new MissingObjectException(me, Constants.TYPE_TREE);
+		}
 		final byte[] subtreeData = ldr.getCachedBytes();
-		if (ldr.getType() != Constants.OBJ_TREE)
-			throw new IncorrectObjectTypeException(id, Constants.TYPE_TREE);
+		if (ldr.getType() != Constants.OBJ_TREE) {
+			final ObjectId me = id.toObjectId();
+			throw new IncorrectObjectTypeException(me, Constants.TYPE_TREE);
+		}
 		reset(subtreeData);
 	}
 
-	public CanonicalTreeParser createSubtreeIterator(final Repository repo)
+	@Override
+	public CanonicalTreeParser createSubtreeIterator(final Repository repo,
+			final MutableObjectId idBuffer, final WindowCursor curs)
 			throws IncorrectObjectTypeException, IOException {
-		final ObjectId id = getEntryObjectId();
-		if (!FileMode.TREE.equals(mode))
-			throw new IncorrectObjectTypeException(id, Constants.TYPE_TREE);
+		idBuffer.fromRaw(idBuffer(), idOffset());
+		if (!FileMode.TREE.equals(mode)) {
+			final ObjectId me = idBuffer.toObjectId();
+			throw new IncorrectObjectTypeException(me, Constants.TYPE_TREE);
+		}
 		final CanonicalTreeParser p = new CanonicalTreeParser(this);
-		p.reset(repo, id);
+		p.reset(repo, idBuffer, curs);
 		return p;
 	}
 
+	public CanonicalTreeParser createSubtreeIterator(final Repository repo)
+			throws IncorrectObjectTypeException, IOException {
+		final WindowCursor curs = new WindowCursor();
+		try {
+			return createSubtreeIterator(repo, new MutableObjectId(), curs);
+		} finally {
+			curs.release();
+		}
+	}
+
 	@Override
 	public byte[] idBuffer() {
 		return raw;

@@ -44,11 +44,13 @@
 import org.spearce.jgit.errors.IncorrectObjectTypeException;
 import org.spearce.jgit.errors.MissingObjectException;
 import org.spearce.jgit.errors.StopWalkException;
+import org.spearce.jgit.lib.AnyObjectId;
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
 import org.spearce.jgit.lib.MutableObjectId;
 import org.spearce.jgit.lib.ObjectId;
 import org.spearce.jgit.lib.Repository;
+import org.spearce.jgit.lib.WindowCursor;
 import org.spearce.jgit.revwalk.RevTree;
 import org.spearce.jgit.treewalk.filter.PathFilterGroup;
 import org.spearce.jgit.treewalk.filter.TreeFilter;

@@ -99,7 +101,7 @@
 	 *             a tree object was not found.
 	 */
 	public static TreeWalk forPath(final Repository db, final String path,
-			final ObjectId[] trees) throws MissingObjectException,
+			final AnyObjectId[] trees) throws MissingObjectException,
 			IncorrectObjectTypeException, CorruptObjectException, IOException {
 		final TreeWalk r = new TreeWalk(db);
 		r.setFilter(PathFilterGroup.createFromStrings(Collections

@@ -142,6 +144,10 @@ public static TreeWalk forPath(final Repository db, final String path,
 
 	private final Repository db;
 
+	private final MutableObjectId idBuffer = new MutableObjectId();
+
+	private final WindowCursor curs = new WindowCursor();
+
 	private TreeFilter filter;
 
 	AbstractTreeIterator[] trees;

@@ -278,6 +284,46 @@ public void reset() {
 	}
 
 	/**
+	 * Reset this walker to run over a single existing tree.
+	 * 
+	 * @param id
+	 *            the tree we need to parse. The walker will execute over this
+	 *            single tree if the reset is successful.
+	 * @throws MissingObjectException
+	 *             the given tree object does not exist in this repository.
+	 * @throws IncorrectObjectTypeException
+	 *             the given object id does not denote a tree, but instead names
+	 *             some other non-tree type of object. Note that commits are not
+	 *             trees, even if they are sometimes called a "tree-ish".
+	 * @throws CorruptObjectException
+	 *             the object claimed to be a tree, but its contents did not
+	 *             appear to be a tree. The repository may have data corruption.
+	 * @throws IOException
+	 *             a loose object or pack file could not be read.
+	 */
+	public void reset(final AnyObjectId id) throws MissingObjectException,
+			IncorrectObjectTypeException, CorruptObjectException, IOException {
+		if (trees.length == 1) {
+			AbstractTreeIterator o = trees[0];
+			while (o.parent != null)
+				o = o.parent;
+			if (o instanceof CanonicalTreeParser) {
+				o.matches = null;
+				o.matchShift = 0;
+				((CanonicalTreeParser) o).reset(db, id, curs);
+				trees[0] = o;
+			} else {
+				trees[0] = parserFor(id);
+			}
+		} else {
+			trees = new AbstractTreeIterator[] { parserFor(id) };
+		}
+
+		advance = false;
+		depth = 0;
+	}
+
+	/**
 	 * Reset this walker to run over a set of existing trees.
 	 * 
 	 * @param ids

@@ -295,7 +341,7 @@ public void reset() {
 	 * @throws IOException
 	 *             a loose object or pack file could not be read.
 	 */
-	public void reset(final ObjectId[] ids) throws MissingObjectException,
+	public void reset(final AnyObjectId[] ids) throws MissingObjectException,
 			IncorrectObjectTypeException, CorruptObjectException, IOException {
 		final int oldLen = trees.length;
 		final int newLen = ids.length;

@@ -311,7 +357,7 @@ public void reset(final ObjectId[] ids) throws MissingObjectException,
 				if (o instanceof CanonicalTreeParser) {
 					o.matches = null;
 					o.matchShift = 0;
-					((CanonicalTreeParser) o).reset(db, ids[i]);
+					((CanonicalTreeParser) o).reset(db, ids[i], curs);
 					r[i] = o;
 					continue;
 				}

@@ -709,7 +755,7 @@ public void enterSubtree() throws MissingObjectException,
 			final AbstractTreeIterator t = trees[i];
 			final AbstractTreeIterator n;
 			if (t.matches == ch && !t.eof() && FileMode.TREE.equals(t.mode))
-				n = t.createSubtreeIterator(db);
+				n = t.createSubtreeIterator(db, idBuffer, curs);
 			else
 				n = new EmptyTreeIterator(t);
 			tmp[i] = n;

@@ -781,10 +827,10 @@ private void exitSubtree() {
 		currentHead = minRef;
 	}
 
-	private CanonicalTreeParser parserFor(final ObjectId id)
+	private CanonicalTreeParser parserFor(final AnyObjectId id)
 			throws IncorrectObjectTypeException, IOException {
 		final CanonicalTreeParser p = new CanonicalTreeParser();
-		p.reset(db, id);
+		p.reset(db, id, curs);
 		return p;
 	}
 

@@ -46,7 +46,7 @@
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
 import org.spearce.jgit.lib.Repository;
-import org.spearce.jgit.treewalk.TreeWalk;
+import org.spearce.jgit.treewalk.CanonicalTreeParser;
 
 /**
  * Specialized subclass of RevWalk to include trees, blobs and tags.

@@ -74,7 +74,7 @@
 	 */
 	private static final int IN_PENDING = RevWalk.REWRITE;
 
-	private final TreeWalk treeWalk;
+	private CanonicalTreeParser treeWalk;
 
 	private BlockObjQueue pendingObjects;
 

@@ -92,8 +92,8 @@
 	 */
 	public ObjectWalk(final Repository repo) {
 		super(repo);
-		treeWalk = new TreeWalk(repo);
 		pendingObjects = new BlockObjQueue();
+		treeWalk = new CanonicalTreeParser();
 	}
 
 	/**

@@ -240,17 +240,17 @@ public RevObject nextObject() throws MissingObjectException,
 		fromTreeWalk = false;
 
 		if (enterSubtree) {
-			treeWalk.enterSubtree();
+			treeWalk = treeWalk.createSubtreeIterator(db, idBuffer, curs);
 			enterSubtree = false;
 		}
 
-		while (treeWalk.next()) {
-			final FileMode mode = treeWalk.getFileMode(0);
+		for (; !treeWalk.eof(); treeWalk = treeWalk.next()) {
+			final FileMode mode = treeWalk.getEntryFileMode();
 			final int sType = mode.getObjectType();
 
 			switch (sType) {
 			case Constants.OBJ_BLOB: {
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				final RevObject o = lookupAny(idBuffer, sType);
 				if ((o.flags & SEEN) != 0)
 					continue;

@@ -262,7 +262,7 @@ public RevObject nextObject() throws MissingObjectException,
 				return o;
 			}
 			case Constants.OBJ_TREE: {
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				final RevObject o = lookupAny(idBuffer, sType);
 				if ((o.flags & SEEN) != 0)
 					continue;

@@ -277,10 +277,11 @@ public RevObject nextObject() throws MissingObjectException,
 			default:
 				if (FileMode.GITLINK.equals(mode))
 					continue;
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				throw new CorruptObjectException("Invalid mode " + mode
 						+ " for " + idBuffer.name() + " "
-						+ treeWalk.getPathString() + " in " + currentTree + ".");
+						+ treeWalk.getEntryPathString() + " in " + currentTree
+						+ ".");
 			}
 		}
 

@@ -295,7 +296,7 @@ public RevObject nextObject() throws MissingObjectException,
 				continue;
 			if (o instanceof RevTree) {
 				currentTree = (RevTree) o;
-				treeWalk.reset(currentTree);
+				treeWalk = treeWalk.resetRoot(db, currentTree, curs);
 			}
 			return o;
 		}

@@ -353,7 +354,7 @@ public void checkConnectivity() throws MissingObjectException,
 	 *         has no path, such as for annotated tags or root level trees.
 	 */
 	public String getPathString() {
-		return fromTreeWalk ? treeWalk.getPathString() : null;
+		return fromTreeWalk ? treeWalk.getEntryPathString() : null;
 	}
 
 	@Override

@@ -385,33 +386,34 @@ private void markTreeUninteresting(final RevTree tree)
 			return;
 		tree.flags |= UNINTERESTING;
 
-		treeWalk.reset(tree);
-		while (treeWalk.next()) {
-			final FileMode mode = treeWalk.getFileMode(0);
+		treeWalk = treeWalk.resetRoot(db, tree, curs);
+		for (;!treeWalk.eof(); treeWalk = treeWalk.next()) {
+			final FileMode mode = treeWalk.getEntryFileMode();
 			final int sType = mode.getObjectType();
 
 			switch (sType) {
 			case Constants.OBJ_BLOB: {
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				lookupAny(idBuffer, sType).flags |= UNINTERESTING;
 				continue;
 			}
 			case Constants.OBJ_TREE: {
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				final RevObject subtree = lookupAny(idBuffer, sType);
 				if ((subtree.flags & UNINTERESTING) == 0) {
 					subtree.flags |= UNINTERESTING;
-					treeWalk.enterSubtree();
+					treeWalk = treeWalk.createSubtreeIterator(db, idBuffer,
+							curs);
 				}
 				continue;
 			}
 			default:
 				if (FileMode.GITLINK.equals(mode))
 					continue;
-				treeWalk.getObjectId(idBuffer, 0);
+				treeWalk.getEntryObjectId(idBuffer);
 				throw new CorruptObjectException("Invalid mode " + mode
 						+ " for " + idBuffer.name() + " "
-						+ treeWalk.getPathString() + " in " + tree + ".");
+						+ treeWalk.getEntryPathString() + " in " + tree + ".");
 			}
 		}
 	}

@@ -308,6 +308,26 @@ public ObjectId getEntryObjectId() {
 	}
 
 	/**
+	 * Obtain the ObjectId for the current entry.
+	 * 
+	 * @param out
+	 *            buffer to copy the object id into.
+	 */
+	public void getEntryObjectId(final MutableObjectId out) {
+		out.fromRaw(idBuffer(), idOffset());
+	}
+
+	/** @return the file mode of the current entry. */
+	public FileMode getEntryFileMode() {
+		return FileMode.fromBits(mode);
+	}
+
+	/** @return path of the current entry, as a string. */
+	public String getEntryPathString() {
+		return TreeWalk.pathOf(this);
+	}
+
+	/**
 	 * Get the byte array buffer object IDs must be copied out of.
 	 * <p>
 	 * The id buffer contains the bytes necessary to construct an ObjectId for

@@ -52,6 +52,8 @@
 
 /** Parses raw Git trees from the canonical semi-text/semi-binary format. */
 public class CanonicalTreeParser extends AbstractTreeIterator {
+	private static final byte[] EMPTY = {};
+
 	private byte[] raw;
 
 	/** First offset within {@link #raw} of the current entry's data. */

@@ -62,7 +64,7 @@
 
 	/** Create a new parser. */
 	public CanonicalTreeParser() {
-		// Nothing necessary.
+		raw = EMPTY;
 	}
 
 	private CanonicalTreeParser(final CanonicalTreeParser p) {

@@ -92,6 +94,41 @@ public void reset(final byte[] treeData) {
 	 *            messages if data corruption is found.
 	 * @param curs
 	 *            window cursor to use during repository access.
+	 * @return the root level parser.
+	 * @throws MissingObjectException
+	 *             the object supplied is not available from the repository.
+	 * @throws IncorrectObjectTypeException
+	 *             the object supplied as an argument is not actually a tree and
+	 *             cannot be parsed as though it were a tree.
+	 * @throws IOException
+	 *             a loose object or pack file could not be read.
+	 */
+	public CanonicalTreeParser resetRoot(final Repository repo,
+			final AnyObjectId id, final WindowCursor curs)
+			throws IncorrectObjectTypeException, IOException {
+		CanonicalTreeParser p = this;
+		while (p.parent != null)
+			p = (CanonicalTreeParser) p.parent;
+		p.reset(repo, id, curs);
+		return p;
+	}
+
+	/** @return this iterator, or its parent, if the tree is at eof. */
+	public CanonicalTreeParser next() {
+		next(1);
+		return eof() && parent != null ? (CanonicalTreeParser) parent : this;
+	}
+
+	/**
+	 * Reset this parser to walk through the given tree.
+	 * 
+	 * @param repo
+	 *            repository to load the tree data from.
+	 * @param id
+	 *            identity of the tree being parsed; used only in exception
+	 *            messages if data corruption is found.
+	 * @param curs
+	 *            window cursor to use during repository access.
 	 * @throws MissingObjectException
 	 *             the object supplied is not available from the repository.
 	 * @throws IncorrectObjectTypeException

@@ -596,7 +596,7 @@ public ObjectId getObjectId(final int nth) {
 	public void getObjectId(final MutableObjectId out, final int nth) {
 		final AbstractTreeIterator t = trees[nth];
 		if (t.matches == currentHead)
-			out.fromRaw(t.idBuffer(), t.idOffset());
+			t.getEntryObjectId(out);
 		else
 			out.clear();
 	}

@@ -834,7 +834,7 @@ private CanonicalTreeParser parserFor(final AnyObjectId id)
 		return p;
 	}
 
-	private static String pathOf(final AbstractTreeIterator t) {
+	static String pathOf(final AbstractTreeIterator t) {
 		return RawParseUtils.decode(Constants.CHARSET, t.path, 0, t.pathLen);
 	}
 }

@@ -40,17 +40,14 @@
 import java.lang.ref.SoftReference;
 
 class UnpackedObjectCache {
-	private static final int CACHE_SZ = 256;
+	private static final int CACHE_SZ = 1024;
 
 	private static final int MB = 1024 * 1024;
 
 	private static final SoftReference<Entry> DEAD;
 
-	private static int hash(final WindowedFile pack, final long position) {
-		int h = pack.hash + (int) position;
-		h += h >>> 16;
-		h += h >>> 8;
-		return h & (CACHE_SZ - 1);
+	private static int hash(final long position) {
+		return (((int) position) << 22) >>> 22;
 	}
 
 	private static int maxByteCount;

@@ -80,7 +77,7 @@ static synchronized void reconfigure(final int dbLimit) {
 	}
 
 	static synchronized Entry get(final WindowedFile pack, final long position) {
-		final Slot e = cache[hash(pack, position)];
+		final Slot e = cache[hash(position)];
 		if (e.provider == pack && e.position == position) {
 			final Entry buf = e.data.get();
 			if (buf != null) {

@@ -96,7 +93,7 @@ static synchronized void store(final WindowedFile pack,
 		if (data.length > maxByteCount)
 			return; // Too large to cache.
 
-		final Slot e = cache[hash(pack, position)];
+		final Slot e = cache[hash(position)];
 		clearEntry(e);
 
 		openByteCount += data.length;

@@ -104,6 +101,7 @@ static synchronized void store(final WindowedFile pack,
 
 		e.provider = pack;
 		e.position = position;
+		e.sz = data.length;
 		e.data = new SoftReference<Entry>(new Entry(data, objectType));
 		moveToHead(e);
 	}

@@ -155,11 +153,10 @@ private static void unlink(final Slot e) {
 	}
 
 	private static void clearEntry(final Slot e) {
-		final Entry old = e.data.get();
-		if (old != null)
-			openByteCount -= old.data.length;
+		openByteCount -= e.sz;
 		e.provider = null;
 		e.data = DEAD;
+		e.sz = 0;
 	}
 
 	private UnpackedObjectCache() {

@@ -186,6 +183,8 @@ Entry(final byte[] aData, final int aType) {
 
 		long position;
 
+		int sz;
+
 		SoftReference<Entry> data = DEAD;
 	}
 }

@@ -46,6 +46,7 @@
 import org.spearce.jgit.errors.StopWalkException;
 import org.spearce.jgit.lib.Constants;
 import org.spearce.jgit.lib.FileMode;
+import org.spearce.jgit.lib.MutableObjectId;
 import org.spearce.jgit.lib.ObjectId;
 import org.spearce.jgit.lib.Repository;
 import org.spearce.jgit.revwalk.RevTree;

@@ -513,7 +514,8 @@ public FileMode getFileMode(final int nth) {
 	 * <p>
 	 * Using this method to compare ObjectId values between trees of this walker
 	 * is very inefficient. Applications should try to use
-	 * {@link #idEqual(int, int)} whenever possible.
+	 * {@link #idEqual(int, int)} or {@link #getObjectId(MutableObjectId, int)}
+	 * whenever possible.
 	 * <p>
 	 * Every tree supplies an object id, even if the tree does not contain the
 	 * current entry. In the latter case {@link ObjectId#zeroId()} is returned.

@@ -521,6 +523,7 @@ public FileMode getFileMode(final int nth) {
 	 * @param nth
 	 *            tree to obtain the object identifier from.
 	 * @return object identifier for the current tree entry.
+	 * @see #getObjectId(MutableObjectId, int)
 	 * @see #idEqual(int, int)
 	 */
 	public ObjectId getObjectId(final int nth) {

@@ -530,6 +533,29 @@ public ObjectId getObjectId(final int nth) {
 	}
 
 	/**
+	 * Obtain the ObjectId for the current entry.
+	 * <p>
+	 * Every tree supplies an object id, even if the tree does not contain the
+	 * current entry. In the latter case {@link ObjectId#zeroId()} is supplied.
+	 * <p>
+	 * Applications should try to use {@link #idEqual(int, int)} when possible
+	 * as it avoids conversion overheads.
+	 * 
+	 * @param out
+	 *            buffer to copy the object id into.
+	 * @param nth
+	 *            tree to obtain the object identifier from.
+	 * @see #idEqual(int, int)
+	 */
+	public void getObjectId(final MutableObjectId out, final int nth) {
+		final AbstractTreeIterator t = trees[nth];
+		if (t.matches == currentHead)
+			out.fromRaw(t.idBuffer(), t.idOffset());
+		else
+			out.clear();
+	}
+
+	/**
 	 * Compare two tree's current ObjectId values for equality.
 	 * 
 	 * @param nthA