Merge "Fix MissingObjectException race in ObjectDirectory"

5 files changed, 290 insertions, 394 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
index eb4f01caca..a81d8ec0e9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/CachedObjectDirectory.java
@@ -72,11 +72,11 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	 * The set that contains unpacked objects identifiers, it is created when
 	 * the cached instance is created.
 	 */
-	private final ObjectIdOwnerMap<UnpackedObjectId> unpackedObjects = new ObjectIdOwnerMap<UnpackedObjectId>();
+	private ObjectIdOwnerMap<UnpackedObjectId> unpackedObjects;
 
 	private final ObjectDirectory wrapped;
 
-	private AlternateHandle[] alts;
+	private CachedObjectDirectory[] alts;
 
 	/**
 	 * The constructor
@@ -86,11 +86,15 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	 */
 	CachedObjectDirectory(ObjectDirectory wrapped) {
 		this.wrapped = wrapped;
+		this.unpackedObjects = scanLoose();
+	}
 
+	private ObjectIdOwnerMap<UnpackedObjectId> scanLoose() {
+		ObjectIdOwnerMap<UnpackedObjectId> m = new ObjectIdOwnerMap<UnpackedObjectId>();
 		File objects = wrapped.getDirectory();
 		String[] fanout = objects.list();
 		if (fanout == null)
-			fanout = new String[0];
+			return m;
 		for (String d : fanout) {
 			if (d.length() != 2)
 				continue;
@@ -102,12 +106,13 @@ class CachedObjectDirectory extends FileObjectDatabase {
 					continue;
 				try {
 					ObjectId id = ObjectId.fromString(d + e);
-					unpackedObjects.add(new UnpackedObjectId(id));
+					m.add(new UnpackedObjectId(id));
 				} catch (IllegalArgumentException notAnObject) {
 					// ignoring the file that does not represent loose object
 				}
 			}
 		}
+		return m;
 	}
 
 	@Override
@@ -121,13 +126,13 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	}
 
 	@Override
-	FileObjectDatabase newCachedFileObjectDatabase() {
-		return this;
+	File getDirectory() {
+		return wrapped.getDirectory();
 	}
 
 	@Override
-	File getDirectory() {
-		return wrapped.getDirectory();
+	File fileFor(AnyObjectId id) {
+		return wrapped.fileFor(id);
 	}
 
 	@Override
@@ -145,15 +150,12 @@ class CachedObjectDirectory extends FileObjectDatabase {
 		return wrapped.getShallowCommits();
 	}
 
-	@Override
-	AlternateHandle[] myAlternates() {
+	private CachedObjectDirectory[] myAlternates() {
 		if (alts == null) {
-			AlternateHandle[] src = wrapped.myAlternates();
-			alts = new AlternateHandle[src.length];
-			for (int i = 0; i < alts.length; i++) {
-				FileObjectDatabase s = src[i].db;
-				alts[i] = new AlternateHandle(s.newCachedFileObjectDatabase());
-			}
+			ObjectDirectory.AlternateHandle[] src = wrapped.myAlternates();
+			alts = new CachedObjectDirectory[src.length];
+			for (int i = 0; i < alts.length; i++)
+				alts[i] = src[i].db.newCachedFileObjectDatabase();
 		}
 		return alts;
 	}
@@ -170,61 +172,53 @@ class CachedObjectDirectory extends FileObjectDatabase {
 	}
 
 	@Override
-	boolean tryAgain1() {
-		return wrapped.tryAgain1();
-	}
-
-	@Override
-	public boolean has(final AnyObjectId objectId) {
-		return hasObjectImpl1(objectId);
-	}
-
-	@Override
-	boolean hasObject1(AnyObjectId objectId) {
-		return unpackedObjects.contains(objectId)
-				|| wrapped.hasObject1(objectId);
+	public boolean has(final AnyObjectId objectId) throws IOException {
+		if (unpackedObjects.contains(objectId))
+			return true;
+		if (wrapped.hasPackedObject(objectId))
+			return true;
+		for (CachedObjectDirectory alt : myAlternates()) {
+			if (alt.has(objectId))
+				return true;
+		}
+		return false;
 	}
 
 	@Override
 	ObjectLoader openObject(final WindowCursor curs,
 			final AnyObjectId objectId) throws IOException {
-		return openObjectImpl1(curs, objectId);
-	}
-
-	@Override
-	ObjectLoader openObject1(WindowCursor curs, AnyObjectId objectId)
-			throws IOException {
-		if (unpackedObjects.contains(objectId))
-			return wrapped.openObject2(curs, objectId.name(), objectId);
-		return wrapped.openObject1(curs, objectId);
-	}
-
-	@Override
-	boolean hasObject2(String objectId) {
-		return unpackedObjects.contains(ObjectId.fromString(objectId));
-	}
-
-	@Override
-	ObjectLoader openObject2(WindowCursor curs, String objectName,
-			AnyObjectId objectId) throws IOException {
-		if (unpackedObjects.contains(objectId))
-			return wrapped.openObject2(curs, objectName, objectId);
+		ObjectLoader ldr = openLooseObject(curs, objectId);
+		if (ldr != null)
+			return ldr;
+		ldr = wrapped.openPackedObject(curs, objectId);
+		if (ldr != null)
+			return ldr;
+		for (CachedObjectDirectory alt : myAlternates()) {
+			ldr = alt.openObject(curs, objectId);
+			if (ldr != null)
+				return ldr;
+		}
 		return null;
 	}
 
 	@Override
-	long getObjectSize1(WindowCursor curs, AnyObjectId objectId) throws IOException {
-		if (unpackedObjects.contains(objectId))
-			return wrapped.getObjectSize2(curs, objectId.name(), objectId);
-		return wrapped.getObjectSize1(curs, objectId);
+	long getObjectSize(WindowCursor curs, AnyObjectId objectId)
+			throws IOException {
+		// Object size is unlikely to be requested from contexts using
+		// this type. Don't bother trying to accelerate the lookup.
+		return wrapped.getObjectSize(curs, objectId);
 	}
 
 	@Override
-	long getObjectSize2(WindowCursor curs, String objectName, AnyObjectId objectId)
+	ObjectLoader openLooseObject(WindowCursor curs, AnyObjectId id)
 			throws IOException {
-		if (unpackedObjects.contains(objectId))
-			return wrapped.getObjectSize2(curs, objectName, objectId);
-		return -1;
+		if (unpackedObjects.contains(id)) {
+			ObjectLoader ldr = wrapped.openLooseObject(curs, id);
+			if (ldr != null)
+				return ldr;
+			unpackedObjects = scanLoose();
+		}
+		return null;
 	}
 
 	@Override
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
index ba45334bd3..3afc050ba6 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileObjectDatabase.java
@@ -74,61 +74,6 @@ abstract class FileObjectDatabase extends ObjectDatabase {
 		return new ObjectDirectoryInserter(this, getConfig());
 	}
 
-	/**
-	 * Does the requested object exist in this database?
-	 * <p>
-	 * Alternates (if present) are searched automatically.
-	 *
-	 * @param objectId
-	 *            identity of the object to test for existence of.
-	 * @return true if the specified object is stored in this database, or any
-	 *         of the alternate databases.
-	 */
-	public boolean has(final AnyObjectId objectId) {
-		return hasObjectImpl1(objectId) || hasObjectImpl2(objectId.name());
-	}
-
-	/**
-	 * Compute the location of a loose object file.
-	 *
-	 * @param objectId
-	 *            identity of the loose object to map to the directory.
-	 * @return location of the object, if it were to exist as a loose object.
-	 */
-	File fileFor(final AnyObjectId objectId) {
-		return fileFor(objectId.name());
-	}
-
-	File fileFor(final String objectName) {
-		final String d = objectName.substring(0, 2);
-		final String f = objectName.substring(2);
-		return new File(new File(getDirectory(), d), f);
-	}
-
-	final boolean hasObjectImpl1(final AnyObjectId objectId) {
-		if (hasObject1(objectId))
-			return true;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			if (alt.db.hasObjectImpl1(objectId))
-				return true;
-		}
-
-		return tryAgain1() && hasObject1(objectId);
-	}
-
-	final boolean hasObjectImpl2(final String objectId) {
-		if (hasObject2(objectId))
-			return true;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			if (alt.db.hasObjectImpl2(objectId))
-				return true;
-		}
-
-		return false;
-	}
-
 	abstract void resolve(Set<ObjectId> matches, AbbreviatedObjectId id)
 			throws IOException;
 
@@ -138,180 +83,26 @@ abstract class FileObjectDatabase extends ObjectDatabase {
 
 	abstract Set<ObjectId> getShallowCommits() throws IOException;
 
-	/**
-	 * Open an object from this database.
-	 * <p>
-	 * Alternates (if present) are searched automatically.
-	 *
-	 * @param curs
-	 *            temporary working space associated with the calling thread.
-	 * @param objectId
-	 *            identity of the object to open.
-	 * @return a {@link ObjectLoader} for accessing the data of the named
-	 *         object, or null if the object does not exist.
-	 * @throws IOException
-	 */
-	ObjectLoader openObject(final WindowCursor curs, final AnyObjectId objectId)
-			throws IOException {
-		ObjectLoader ldr;
-
-		ldr = openObjectImpl1(curs, objectId);
-		if (ldr != null)
-			return ldr;
-
-		ldr = openObjectImpl2(curs, objectId.name(), objectId);
-		if (ldr != null)
-			return ldr;
-
-		return null;
-	}
-
-	final ObjectLoader openObjectImpl1(final WindowCursor curs,
-			final AnyObjectId objectId) throws IOException {
-		ObjectLoader ldr;
-
-		ldr = openObject1(curs, objectId);
-		if (ldr != null)
-			return ldr;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			ldr = alt.db.openObjectImpl1(curs, objectId);
-			if (ldr != null)
-				return ldr;
-		}
-
-		if (tryAgain1()) {
-			ldr = openObject1(curs, objectId);
-			if (ldr != null)
-				return ldr;
-		}
-
-		return null;
-	}
-
-	final ObjectLoader openObjectImpl2(final WindowCursor curs,
-			final String objectName, final AnyObjectId objectId)
-			throws IOException {
-		ObjectLoader ldr;
-
-		ldr = openObject2(curs, objectName, objectId);
-		if (ldr != null)
-			return ldr;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			ldr = alt.db.openObjectImpl2(curs, objectName, objectId);
-			if (ldr != null)
-				return ldr;
-		}
-
-		return null;
-	}
-
-	long getObjectSize(WindowCursor curs, AnyObjectId objectId)
-			throws IOException {
-		long sz = getObjectSizeImpl1(curs, objectId);
-		if (0 <= sz)
-			return sz;
-		return getObjectSizeImpl2(curs, objectId.name(), objectId);
-	}
-
-	final long getObjectSizeImpl1(final WindowCursor curs,
-			final AnyObjectId objectId) throws IOException {
-		long sz;
-
-		sz = getObjectSize1(curs, objectId);
-		if (0 <= sz)
-			return sz;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			sz = alt.db.getObjectSizeImpl1(curs, objectId);
-			if (0 <= sz)
-				return sz;
-		}
-
-		if (tryAgain1()) {
-			sz = getObjectSize1(curs, objectId);
-			if (0 <= sz)
-				return sz;
-		}
-
-		return -1;
-	}
-
-	final long getObjectSizeImpl2(final WindowCursor curs,
-			final String objectName, final AnyObjectId objectId)
-			throws IOException {
-		long sz;
-
-		sz = getObjectSize2(curs, objectName, objectId);
-		if (0 <= sz)
-			return sz;
-
-		for (final AlternateHandle alt : myAlternates()) {
-			sz = alt.db.getObjectSizeImpl2(curs, objectName, objectId);
-			if (0 <= sz)
-				return sz;
-		}
-
-		return -1;
-	}
-
 	abstract void selectObjectRepresentation(PackWriter packer,
 			ObjectToPack otp, WindowCursor curs) throws IOException;
 
 	abstract File getDirectory();
 
-	abstract AlternateHandle[] myAlternates();
+	abstract File fileFor(AnyObjectId id);
 
-	abstract boolean tryAgain1();
-
-	abstract boolean hasObject1(AnyObjectId objectId);
-
-	abstract boolean hasObject2(String objectId);
-
-	abstract ObjectLoader openObject1(WindowCursor curs, AnyObjectId objectId)
+	abstract ObjectLoader openObject(WindowCursor curs, AnyObjectId objectId)
 			throws IOException;
 
-	abstract ObjectLoader openObject2(WindowCursor curs, String objectName,
-			AnyObjectId objectId) throws IOException;
-
-	abstract long getObjectSize1(WindowCursor curs, AnyObjectId objectId)
+	abstract long getObjectSize(WindowCursor curs, AnyObjectId objectId)
 			throws IOException;
 
-	abstract long getObjectSize2(WindowCursor curs, String objectName,
-			AnyObjectId objectId) throws IOException;
+	abstract ObjectLoader openLooseObject(WindowCursor curs, AnyObjectId id)
+			throws IOException;
 
 	abstract InsertLooseObjectResult insertUnpackedObject(File tmp,
 			ObjectId id, boolean createDuplicate) throws IOException;
 
 	abstract PackFile openPack(File pack) throws IOException;
 
-	abstract FileObjectDatabase newCachedFileObjectDatabase();
-
 	abstract Collection<PackFile> getPacks();
-
-	static class AlternateHandle {
-		final FileObjectDatabase db;
-
-		AlternateHandle(FileObjectDatabase db) {
-			this.db = db;
-		}
-
-		void close() {
-			db.close();
-		}
-	}
-
-	static class AlternateRepository extends AlternateHandle {
-		final FileRepository repository;
-
-		AlternateRepository(FileRepository r) {
-			super(r.getObjectDatabase());
-			repository = r;
-		}
-
-		void close() {
-			repository.close();
-		}
-	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
index 33026aad72..148781dfe9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/FileRepository.java
@@ -59,8 +59,8 @@ import org.eclipse.jgit.events.ConfigChangedEvent;
 import org.eclipse.jgit.events.ConfigChangedListener;
 import org.eclipse.jgit.events.IndexChangedEvent;
 import org.eclipse.jgit.internal.JGitText;
-import org.eclipse.jgit.internal.storage.file.FileObjectDatabase.AlternateHandle;
-import org.eclipse.jgit.internal.storage.file.FileObjectDatabase.AlternateRepository;
+import org.eclipse.jgit.internal.storage.file.ObjectDirectory.AlternateHandle;
+import org.eclipse.jgit.internal.storage.file.ObjectDirectory.AlternateRepository;
 import org.eclipse.jgit.lib.BaseRepositoryBuilder;
 import org.eclipse.jgit.lib.ConfigConstants;
 import org.eclipse.jgit.lib.Constants;
@@ -368,7 +368,7 @@ public class FileRepository extends Repository {
 	 */
 	public Set<ObjectId> getAdditionalHaves() {
 		HashSet<ObjectId> r = new HashSet<ObjectId>();
-		for (AlternateHandle d : objectDatabase. myAlternates()) {
+		for (AlternateHandle d : objectDatabase.myAlternates()) {
 			if (d instanceof AlternateRepository) {
 				Repository repo;
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedDeltaObject.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedDeltaObject.java
index f6bbae2b91..18f15b068c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedDeltaObject.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/LargePackedDeltaObject.java
@@ -173,7 +173,7 @@ class LargePackedDeltaObject extends ObjectLoader {
 		//
 		final ObjectId myId = getObjectId();
 		final WindowCursor wc = new WindowCursor(db);
-		ObjectLoader ldr = db.openObject2(wc, myId.name(), myId);
+		ObjectLoader ldr = db.openLooseObject(wc, myId);
 		if (ldr != null)
 			return ldr.openStream();
 
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
index 3b6901bd51..1795683aa8 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
@@ -200,32 +200,20 @@ public class ObjectDirectory extends FileObjectDatabase {
 		unpackedObjectCache.clear();
 
 		final PackList packs = packList.get();
-		packList.set(NO_PACKS);
-		for (final PackFile p : packs.packs)
-			p.close();
+		if (packs != NO_PACKS && packList.compareAndSet(packs, NO_PACKS)) {
+			for (PackFile p : packs.packs)
+				p.close();
+		}
 
 		// Fully close all loaded alternates and clear the alternate list.
 		AlternateHandle[] alt = alternates.get();
-		if (alt != null) {
-			alternates.set(null);
+		if (alt != null && alternates.compareAndSet(alt, null)) {
 			for(final AlternateHandle od : alt)
 				od.close();
 		}
 	}
 
 	/**
-	 * Compute the location of a loose object file.
-	 *
-	 * @param objectId
-	 *            identity of the loose object to map to the directory.
-	 * @return location of the object, if it were to exist as a loose object.
-	 */
-	@Override
-	public File fileFor(final AnyObjectId objectId) {
-		return super.fileFor(objectId);
-	}
-
-	/**
 	 * @return unmodifiable collection of all known pack files local to this
 	 *         directory. Most recent packs are presented first. Packs most
 	 *         likely to contain more recent objects appear before packs
@@ -277,37 +265,64 @@ public class ObjectDirectory extends FileObjectDatabase {
 
 	@Override
 	public String toString() {
-		return "ObjectDirectory[" + getDirectory() + "]"; //$NON-NLS-1$
+		return "ObjectDirectory[" + getDirectory() + "]"; //$NON-NLS-1$ //$NON-NLS-2$
+	}
+
+	@Override
+	public boolean has(AnyObjectId objectId) {
+		return unpackedObjectCache.isUnpacked(objectId)
+				|| hasPackedInSelfOrAlternate(objectId)
+				|| hasLooseInSelfOrAlternate(objectId);
 	}
 
-	boolean hasObject1(final AnyObjectId objectId) {
-		if (unpackedObjectCache.isUnpacked(objectId))
+	private boolean hasPackedInSelfOrAlternate(AnyObjectId objectId) {
+		if (hasPackedObject(objectId))
 			return true;
-		for (final PackFile p : packList.get().packs) {
-			try {
-				if (p.hasObject(objectId)) {
-					return true;
+		for (AlternateHandle alt : myAlternates()) {
+			if (alt.db.hasPackedInSelfOrAlternate(objectId))
+				return true;
+		}
+		return false;
+	}
+
+	private boolean hasLooseInSelfOrAlternate(AnyObjectId objectId) {
+		if (fileFor(objectId).exists())
+			return true;
+		for (AlternateHandle alt : myAlternates()) {
+			if (alt.db.hasLooseInSelfOrAlternate(objectId))
+				return true;
+		}
+		return false;
+	}
+
+	boolean hasPackedObject(AnyObjectId objectId) {
+		PackList pList;
+		do {
+			pList = packList.get();
+			for (PackFile p : pList.packs) {
+				try {
+					if (p.hasObject(objectId))
+						return true;
+				} catch (IOException e) {
+					// The hasObject call should have only touched the index,
+					// so any failure here indicates the index is unreadable
+					// by this process, and the pack is likewise not readable.
+					removePack(p);
 				}
-			} catch (IOException e) {
-				// The hasObject call should have only touched the index,
-				// so any failure here indicates the index is unreadable
-				// by this process, and the pack is likewise not readable.
-				//
-				removePack(p);
-				continue;
 			}
-		}
+		} while (searchPacksAgain(pList));
 		return false;
 	}
 
+	@Override
 	void resolve(Set<ObjectId> matches, AbbreviatedObjectId id)
 			throws IOException {
 		// Go through the packs once. If we didn't find any resolutions
 		// scan for new packs and check once more.
-		//
 		int oldSize = matches.size();
-		PackList pList = packList.get();
-		for (;;) {
+		PackList pList;
+		do {
+			pList = packList.get();
 			for (PackFile p : pList.packs) {
 				try {
 					p.resolve(matches, id, RESOLVE_ABBREV_LIMIT);
@@ -319,15 +334,7 @@ public class ObjectDirectory extends FileObjectDatabase {
 				if (matches.size() > RESOLVE_ABBREV_LIMIT)
 					return;
 			}
-			if (matches.size() == oldSize) {
-				PackList nList = scanPacks(pList);
-				if (nList == pList || nList.packs.length == 0)
-					break;
-				pList = nList;
-				continue;
-			}
-			break;
-		}
+		} while (matches.size() == oldSize && searchPacksAgain(pList));
 
 		String fanOut = id.name().substring(0, 2);
 		String[] entries = new File(getDirectory(), fanOut).list();
@@ -354,74 +361,164 @@ public class ObjectDirectory extends FileObjectDatabase {
 		}
 	}
 
-	ObjectLoader openObject1(final WindowCursor curs,
-			final AnyObjectId objectId) throws IOException {
+	@Override
+	ObjectLoader openObject(WindowCursor curs, AnyObjectId objectId)
+			throws IOException {
 		if (unpackedObjectCache.isUnpacked(objectId)) {
-			ObjectLoader ldr = openObject2(curs, objectId.name(), objectId);
+			ObjectLoader ldr = openLooseObject(curs, objectId);
 			if (ldr != null)
 				return ldr;
-			else
-				unpackedObjectCache.remove(objectId);
 		}
+		ObjectLoader ldr = openPackedFromSelfOrAlternate(curs, objectId);
+		if (ldr != null)
+			return ldr;
+		return openLooseFromSelfOrAlternate(curs, objectId);
+	}
 
-		PackList pList = packList.get();
-		SEARCH: for (;;) {
-			for (final PackFile p : pList.packs) {
-				try {
-					final ObjectLoader ldr = p.get(curs, objectId);
-					if (ldr != null)
-						return ldr;
-				} catch (PackMismatchException e) {
-					// Pack was modified; refresh the entire pack list.
-					//
-					pList = scanPacks(pList);
-					continue SEARCH;
-				} catch (IOException e) {
-					// Assume the pack is corrupted.
-					//
-					removePack(p);
+	private ObjectLoader openPackedFromSelfOrAlternate(WindowCursor curs,
+			AnyObjectId objectId) {
+		ObjectLoader ldr = openPackedObject(curs, objectId);
+		if (ldr != null)
+			return ldr;
+		for (AlternateHandle alt : myAlternates()) {
+			ldr = alt.db.openPackedFromSelfOrAlternate(curs, objectId);
+			if (ldr != null)
+				return ldr;
+		}
+		return null;
+	}
+
+	private ObjectLoader openLooseFromSelfOrAlternate(WindowCursor curs,
+			AnyObjectId objectId) throws IOException {
+		ObjectLoader ldr = openLooseObject(curs, objectId);
+		if (ldr != null)
+			return ldr;
+		for (AlternateHandle alt : myAlternates()) {
+			ldr = alt.db.openLooseFromSelfOrAlternate(curs, objectId);
+			if (ldr != null)
+				return ldr;
+		}
+		return null;
+	}
+
+	ObjectLoader openPackedObject(WindowCursor curs, AnyObjectId objectId) {
+		PackList pList;
+		do {
+			SEARCH: for (;;) {
+				pList = packList.get();
+				for (PackFile p : pList.packs) {
+					try {
+						ObjectLoader ldr = p.get(curs, objectId);
+						if (ldr != null)
+							return ldr;
+					} catch (PackMismatchException e) {
+						// Pack was modified; refresh the entire pack list.
+						if (searchPacksAgain(pList))
+							continue SEARCH;
+					} catch (IOException e) {
+						// Assume the pack is corrupted.
+						removePack(p);
+					}
 				}
+				break SEARCH;
 			}
+		} while (searchPacksAgain(pList));
+		return null;
+	}
+
+	ObjectLoader openLooseObject(WindowCursor curs, AnyObjectId id)
+			throws IOException {
+		try {
+			File path = fileFor(id);
+			FileInputStream in = new FileInputStream(path);
+			try {
+				unpackedObjectCache.add(id);
+				return UnpackedObject.open(in, path, id, curs);
+			} finally {
+				in.close();
+			}
+		} catch (FileNotFoundException noFile) {
+			unpackedObjectCache.remove(id);
 			return null;
 		}
 	}
 
-	long getObjectSize1(final WindowCursor curs, final AnyObjectId objectId)
+	long getObjectSize(WindowCursor curs, AnyObjectId id)
 			throws IOException {
-		PackList pList = packList.get();
-		SEARCH: for (;;) {
-			for (final PackFile p : pList.packs) {
-				try {
-					long sz = p.getObjectSize(curs, objectId);
-					if (0 <= sz)
-						return sz;
-				} catch (PackMismatchException e) {
-					// Pack was modified; refresh the entire pack list.
-					//
-					pList = scanPacks(pList);
-					continue SEARCH;
-				} catch (IOException e) {
-					// Assume the pack is corrupted.
-					//
-					removePack(p);
+		if (unpackedObjectCache.isUnpacked(id)) {
+			long len = getLooseObjectSize(curs, id);
+			if (0 <= len)
+				return len;
+		}
+		long len = getPackedSizeFromSelfOrAlternate(curs, id);
+		if (0 <= len)
+			return len;
+		return getLooseSizeFromSelfOrAlternate(curs, id);
+	}
+
+	private long getPackedSizeFromSelfOrAlternate(WindowCursor curs,
+			AnyObjectId id) {
+		long len = getPackedObjectSize(curs, id);
+		if (0 <= len)
+			return len;
+		for (AlternateHandle alt : myAlternates()) {
+			len = alt.db.getPackedSizeFromSelfOrAlternate(curs, id);
+			if (0 <= len)
+				return len;
+		}
+		return -1;
+	}
+
+	private long getLooseSizeFromSelfOrAlternate(WindowCursor curs,
+			AnyObjectId id) throws IOException {
+		long len = getLooseObjectSize(curs, id);
+		if (0 <= len)
+			return len;
+		for (AlternateHandle alt : myAlternates()) {
+			len = alt.db.getLooseSizeFromSelfOrAlternate(curs, id);
+			if (0 <= len)
+				return len;
+		}
+		return -1;
+	}
+
+	private long getPackedObjectSize(WindowCursor curs, AnyObjectId id) {
+		PackList pList;
+		do {
+			SEARCH: for (;;) {
+				pList = packList.get();
+				for (PackFile p : pList.packs) {
+					try {
+						long len = p.getObjectSize(curs, id);
+						if (0 <= len)
+							return len;
+					} catch (PackMismatchException e) {
+						// Pack was modified; refresh the entire pack list.
+						if (searchPacksAgain(pList))
+							continue SEARCH;
+					} catch (IOException e) {
+						// Assume the pack is corrupted.
+						removePack(p);
+					}
 				}
+				break SEARCH;
 			}
-			return -1;
-		}
+		} while (searchPacksAgain(pList));
+		return -1;
 	}
 
-	@Override
-	long getObjectSize2(WindowCursor curs, String objectName,
-			AnyObjectId objectId) throws IOException {
+	private long getLooseObjectSize(WindowCursor curs, AnyObjectId id)
+			throws IOException {
 		try {
-			File path = fileFor(objectName);
-			FileInputStream in = new FileInputStream(path);
+			FileInputStream in = new FileInputStream(fileFor(id));
 			try {
-				return UnpackedObject.getSize(in, objectId, curs);
+				unpackedObjectCache.add(id);
+				return UnpackedObject.getSize(in, id, curs);
 			} finally {
 				in.close();
 			}
 		} catch (FileNotFoundException noFile) {
+			unpackedObjectCache.remove(id);
 			return -1;
 		}
 	}
@@ -454,28 +551,6 @@ public class ObjectDirectory extends FileObjectDatabase {
 			h.db.selectObjectRepresentation(packer, otp, curs);
 	}
 
-	boolean hasObject2(final String objectName) {
-		return fileFor(objectName).exists();
-	}
-
-	ObjectLoader openObject2(final WindowCursor curs,
-			final String objectName, final AnyObjectId objectId)
-			throws IOException {
-		try {
-			File path = fileFor(objectName);
-			FileInputStream in = new FileInputStream(path);
-			try {
-				unpackedObjectCache.add(objectId);
-				return UnpackedObject.open(in, path, objectId, curs);
-			} finally {
-				in.close();
-			}
-		} catch (FileNotFoundException noFile) {
-			unpackedObjectCache.remove(objectId);
-			return null;
-		}
-	}
-
 	@Override
 	InsertLooseObjectResult insertUnpackedObject(File tmp, ObjectId id,
 			boolean createDuplicate) throws IOException {
@@ -530,11 +605,8 @@ public class ObjectDirectory extends FileObjectDatabase {
 		return InsertLooseObjectResult.FAILURE;
 	}
 
-	boolean tryAgain1() {
-		final PackList old = packList.get();
-		if (old.snapshot.isModified(packDirectory))
-			return old != scanPacks(old);
-		return false;
+	private boolean searchPacksAgain(PackList old) {
+		return old.snapshot.isModified(packDirectory) && old != scanPacks(old);
 	}
 
 	Config getConfig() {
@@ -794,6 +866,20 @@ public class ObjectDirectory extends FileObjectDatabase {
 		return new AlternateHandle(db);
 	}
 
+	/**
+	 * Compute the location of a loose object file.
+	 *
+	 * @param objectId
+	 *            identity of the loose object to map to the directory.
+	 * @return location of the object, if it were to exist as a loose object.
+	 */
+	public File fileFor(AnyObjectId objectId) {
+		String n = objectId.name();
+		String d = n.substring(0, 2);
+		String f = n.substring(2);
+		return new File(new File(getDirectory(), d), f);
+	}
+
 	private static final class PackList {
 		/** State just before reading the pack directory. */
 		final FileSnapshot snapshot;
@@ -807,12 +893,37 @@ public class ObjectDirectory extends FileObjectDatabase {
 		}
 	}
 
+	static class AlternateHandle {
+		final ObjectDirectory db;
+
+		AlternateHandle(ObjectDirectory db) {
+			this.db = db;
+		}
+
+		void close() {
+			db.close();
+		}
+	}
+
+	static class AlternateRepository extends AlternateHandle {
+		final FileRepository repository;
+
+		AlternateRepository(FileRepository r) {
+			super(r.getObjectDatabase());
+			repository = r;
+		}
+
+		void close() {
+			repository.close();
+		}
+	}
+
 	@Override
 	public ObjectDatabase newCachedDatabase() {
 		return newCachedFileObjectDatabase();
 	}
 
-	FileObjectDatabase newCachedFileObjectDatabase() {
+	CachedObjectDirectory newCachedFileObjectDatabase() {
 		return new CachedObjectDirectory(this);
 	}
 }