patch, 5 partsRemove throws IOException from UnpackedObjectLoader.getCachedBytes

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
index 7552b42..1352b72 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
@@ -201,7 +201,7 @@ public long getSize() {
 	}
 
 	@Override
-	public byte[] getCachedBytes() throws IOException {
+	public byte[] getCachedBytes() {
 		return bytes;
 	}
 

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
index 1352b72..e2de41c 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/UnpackedObjectLoader.java
@@ -192,10 +192,12 @@ private void decompress(final AnyObjectId id, final Inflater inf, int p)
 			throw new CorruptObjectException(id, "incorrect length");
 	}
 
+	@Override
 	public int getType() {
 		return objectType;
 	}
 
+	@Override
 	public long getSize() {
 		return objectSize;
 	}

org.spearce.jgit/src/org/spearce/jgit/lib/DeltaOfsPackedObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/DeltaRefPackedObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/ObjectDirectory.java, org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java, org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java, org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/WholePackedObjectLoader.java

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaOfsPackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaOfsPackedObjectLoader.java
index 5c9fb00..ee2a0de 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaOfsPackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaOfsPackedObjectLoader.java
@@ -46,14 +46,15 @@
 class DeltaOfsPackedObjectLoader extends DeltaPackedObjectLoader {
 	private final long deltaBase;
 
-	DeltaOfsPackedObjectLoader(final WindowCursor curs, final PackFile pr,
+	DeltaOfsPackedObjectLoader(final PackFile pr,
 			final long dataOffset, final long objectOffset, final int deltaSz,
 			final long base) {
-		super(curs, pr, dataOffset, objectOffset, deltaSz);
+		super(pr, dataOffset, objectOffset, deltaSz);
 		deltaBase = base;
 	}
 
-	protected PackedObjectLoader getBaseLoader() throws IOException {
+	protected PackedObjectLoader getBaseLoader(final WindowCursor curs)
+			throws IOException {
 		return pack.resolveBase(curs, deltaBase);
 	}
 
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java
index 85f2bda..8194d94 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java
@@ -49,47 +49,39 @@
 
 	private final int deltaSize;
 
-	DeltaPackedObjectLoader(final WindowCursor curs, final PackFile pr,
-			final long dataOffset, final long objectOffset, final int deltaSz) {
-		super(curs, pr, dataOffset, objectOffset);
+	DeltaPackedObjectLoader(final PackFile pr, final long dataOffset,
+			final long objectOffset, final int deltaSz) {
+		super(pr, dataOffset, objectOffset);
 		objectType = -1;
 		deltaSize = deltaSz;
 	}
 
-	public int getType() throws IOException {
-		if (objectType < 0)
-			getCachedBytes();
-		return objectType;
-	}
-
-	public long getSize() throws IOException {
-		if (objectType < 0)
-			getCachedBytes();
-		return objectSize;
-	}
-
 	@Override
-	public byte[] getCachedBytes() throws IOException {
+	public void materialize(final WindowCursor curs) throws IOException {
+		if (cachedBytes != null) {
+			return;
+		}
+
 		if (objectType != OBJ_COMMIT) {
 			final UnpackedObjectCache.Entry cache = pack.readCache(dataOffset);
 			if (cache != null) {
 				curs.release();
 				objectType = cache.type;
 				objectSize = cache.data.length;
-				return cache.data;
+				cachedBytes = cache.data;
 			}
 		}
 
 		try {
-			final PackedObjectLoader baseLoader = getBaseLoader();
-			final byte[] data = BinaryDelta.apply(baseLoader.getCachedBytes(),
+			final PackedObjectLoader baseLoader = getBaseLoader(curs);
+			baseLoader.materialize(curs);
+			cachedBytes = BinaryDelta.apply(baseLoader.getCachedBytes(),
 					pack.decompress(dataOffset, deltaSize, curs));
 			curs.release();
 			objectType = baseLoader.getType();
-			objectSize = data.length;
+			objectSize = cachedBytes.length;
 			if (objectType != OBJ_COMMIT)
-				pack.saveCache(dataOffset, data, objectType);
-			return data;
+				pack.saveCache(dataOffset, cachedBytes, objectType);
 		} catch (DataFormatException dfe) {
 			final CorruptObjectException coe;
 			coe = new CorruptObjectException("Object at " + dataOffset + " in "
@@ -105,8 +97,11 @@ public long getRawSize() {
 	}
 
 	/**
+	 * @param curs
+	 *            temporary thread storage during data access.
 	 * @return the object loader for the base object
 	 * @throws IOException
 	 */
-	protected abstract PackedObjectLoader getBaseLoader() throws IOException;
+	protected abstract PackedObjectLoader getBaseLoader(WindowCursor curs)
+			throws IOException;
 }
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaRefPackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaRefPackedObjectLoader.java
index b126bbd..82a3a7f 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaRefPackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaRefPackedObjectLoader.java
@@ -46,14 +46,15 @@
 class DeltaRefPackedObjectLoader extends DeltaPackedObjectLoader {
 	private final ObjectId deltaBase;
 
-	DeltaRefPackedObjectLoader(final WindowCursor curs, final PackFile pr,
+	DeltaRefPackedObjectLoader(final PackFile pr,
 			final long dataOffset, final long objectOffset, final int deltaSz,
 			final ObjectId base) {
-		super(curs, pr, dataOffset, objectOffset, deltaSz);
+		super(pr, dataOffset, objectOffset, deltaSz);
 		deltaBase = base;
 	}
 
-	protected PackedObjectLoader getBaseLoader() throws IOException {
+	protected PackedObjectLoader getBaseLoader(final WindowCursor curs)
+			throws IOException {
 		final PackedObjectLoader or = pack.get(curs, deltaBase);
 		if (or == null)
 			throw new MissingObjectException(deltaBase, "delta base");
@@ -61,7 +62,7 @@ protected PackedObjectLoader getBaseLoader() throws IOException {
 	}
 
 	@Override
-	public int getRawType() throws IOException {
+	public int getRawType() {
 		return Constants.OBJ_REF_DELTA;
 	}
 
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectDirectory.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectDirectory.java
index 6ba0180..3e9ed1c 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectDirectory.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectDirectory.java
@@ -197,8 +197,9 @@ protected ObjectLoader openObject1(final WindowCursor curs,
 		SEARCH: for (;;) {
 			for (final PackFile p : pList) {
 				try {
-					final ObjectLoader ldr = p.get(curs, objectId);
+					final PackedObjectLoader ldr = p.get(curs, objectId);
 					if (ldr != null) {
+						ldr.materialize(curs);
 						return ldr;
 					}
 				} catch (PackMismatchException e) {
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java
index 5485d8d..6b92694 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectLoader.java
@@ -38,7 +38,6 @@
 
 package org.spearce.jgit.lib;
 
-import java.io.IOException;
 
 /**
  * Base class for a set of loaders for different representations of Git objects.
@@ -47,15 +46,13 @@
 public abstract class ObjectLoader {
 	/**
 	 * @return Git in pack object type, see {@link Constants}.
-	 * @throws IOException
 	 */
-	public abstract int getType() throws IOException;
+	public abstract int getType();
 
 	/**
 	 * @return size of object in bytes
-	 * @throws IOException
 	 */
-	public abstract long getSize() throws IOException;
+	public abstract long getSize();
 
 	/**
 	 * Obtain a copy of the bytes of this object.
@@ -64,10 +61,8 @@
 	 * be modified by the caller.
 	 * 
 	 * @return the bytes of this object.
-	 * @throws IOException
-	 *             the object cannot be read.
 	 */
-	public final byte[] getBytes() throws IOException {
+	public final byte[] getBytes() {
 		final byte[] data = getCachedBytes();
 		final byte[] copy = new byte[data.length];
 		System.arraycopy(data, 0, copy, 0, data.length);
@@ -83,25 +78,19 @@
 	 * Changes (if made) will affect the cache but not the repository itself.
 	 * 
 	 * @return the cached bytes of this object. Do not modify it.
-	 * @throws IOException
-	 *             the object cannot be read.
 	 */
-	public abstract byte[] getCachedBytes() throws IOException;
+	public abstract byte[] getCachedBytes();
 
 	/**
 	 * @return raw object type from object header, as stored in storage (pack,
 	 *         loose file). This may be different from {@link #getType()} result
 	 *         for packs (see {@link Constants}).
-	 * @throws IOException
-	 *             when type cannot be read from the object header.
 	 */
-	public abstract int getRawType() throws IOException;
+	public abstract int getRawType();
 
 	/**
 	 * @return raw size of object from object header (pack, loose file).
 	 *         Interpretation of this value depends on {@link #getRawType()}.
-	 * @throws IOException
-	 *             when raw size cannot be read from the object header.
 	 */
-	public abstract long getRawSize() throws IOException;
+	public abstract long getRawSize();
 }
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
index dccc067..813ebc7 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
@@ -244,11 +244,11 @@ final void saveCache(final long position, final byte[] data, final int type) {
 	}
 
 	final void copyRawData(final PackedObjectLoader loader,
-			final OutputStream out, final byte buf[]) throws IOException {
+			final OutputStream out, final byte buf[], final WindowCursor curs)
+			throws IOException {
 		final long objectOffset = loader.objectOffset;
 		final long dataOffset = loader.dataOffset;
 		final int cnt = (int) (findEndOffset(objectOffset) - dataOffset);
-		final WindowCursor curs = loader.curs;
 		final PackIndex idx = idx();
 
 		if (idx.hasCRC32Support()) {
@@ -436,8 +436,8 @@ private PackedObjectLoader reader(final WindowCursor curs,
 		case Constants.OBJ_TREE:
 		case Constants.OBJ_BLOB:
 		case Constants.OBJ_TAG:
-			return new WholePackedObjectLoader(curs, this, pos, objOffset,
-					typeCode, (int) dataSize);
+			return new WholePackedObjectLoader(this, pos, objOffset, typeCode,
+					(int) dataSize);
 
 		case Constants.OBJ_OFS_DELTA: {
 			readFully(pos, ib, 0, 20, curs);
@@ -450,12 +450,12 @@ private PackedObjectLoader reader(final WindowCursor curs,
 				ofs <<= 7;
 				ofs += (c & 127);
 			}
-			return new DeltaOfsPackedObjectLoader(curs, this, pos + p,
-					objOffset, (int) dataSize, objOffset - ofs);
+			return new DeltaOfsPackedObjectLoader(this, pos + p, objOffset,
+					(int) dataSize, objOffset - ofs);
 		}
 		case Constants.OBJ_REF_DELTA: {
 			readFully(pos, ib, 0, 20, curs);
-			return new DeltaRefPackedObjectLoader(curs, this, pos + ib.length,
+			return new DeltaRefPackedObjectLoader(this, pos + ib.length,
 					objOffset, (int) dataSize, ObjectId.fromRaw(ib));
 		}
 		default:
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
index c2e6c4b..e1397fd 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
@@ -720,7 +720,7 @@ private void writeWholeObject(final ObjectToPack otp) throws IOException {
 		if (otp.hasReuseLoader()) {
 			final PackedObjectLoader loader = otp.getReuseLoader();
 			writeObjectHeader(otp.getType(), loader.getSize());
-			loader.copyRawData(out, buf);
+			loader.copyRawData(out, buf, windowCursor);
 			otp.disposeLoader();
 		} else {
 			final ObjectLoader loader = db.openObject(windowCursor, otp);
@@ -756,7 +756,7 @@ private void writeDeltaObject(final ObjectToPack otp) throws IOException {
 			otp.getDeltaBaseId().copyRawTo(buf, 0);
 			out.write(buf, 0, Constants.OBJECT_ID_LENGTH);
 		}
-		loader.copyRawData(out, buf);
+		loader.copyRawData(out, buf, windowCursor);
 		otp.disposeLoader();
 	}
 
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
index 56985c1..60333e7 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
@@ -47,8 +47,6 @@
 abstract class PackedObjectLoader extends ObjectLoader {
 	protected final PackFile pack;
 
-	protected final WindowCursor curs;
-
 	protected final long dataOffset;
 
 	protected final long objectOffset;
@@ -57,26 +55,53 @@
 
 	protected int objectSize;
 
-	PackedObjectLoader(final WindowCursor c, final PackFile pr,
-			final long dataOffset, final long objectOffset) {
-		curs = c;
+	protected byte[] cachedBytes;
+
+	PackedObjectLoader(final PackFile pr, final long dataOffset,
+			final long objectOffset) {
 		pack = pr;
 		this.dataOffset = dataOffset;
 		this.objectOffset = objectOffset;
 	}
 
-	public int getType() throws IOException {
+	/**
+	 * Force this object to be loaded into memory and pinned in this loader.
+	 * <p>
+	 * Once materialized, subsequent get operations for the following methods
+	 * will always succeed without raising an exception, as all information is
+	 * pinned in memory by this loader instance.
+	 * <ul>
+	 * <li>{@link #getType()}</li>
+	 * <li>{@link #getSize()}</li>
+	 * <li>{@link #getBytes()}, {@link #getCachedBytes}</li>
+	 * <li>{@link #getRawSize()}</li>
+	 * <li>{@link #getRawType()}</li>
+	 * </ul>
+	 *
+	 * @param curs
+	 *            temporary thread storage during data access.
+	 * @throws IOException
+	 *             the object cannot be read.
+	 */
+	public abstract void materialize(WindowCursor curs) throws IOException;
+
+	public final int getType() {
 		return objectType;
 	}
 
-	public long getSize() throws IOException {
+	public final long getSize() {
 		return objectSize;
 	}
 
+	@Override
+	public final byte[] getCachedBytes() {
+		return cachedBytes;
+	}
+
 	/**
 	 * @return offset of object data within pack file
 	 */
-	public long getDataOffset() {
+	public final long getDataOffset() {
 		return dataOffset;
 	}
 
@@ -92,11 +117,14 @@ public long getDataOffset() {
 	 * @param buf
 	 *            temporary buffer used during copying. Recommended size is at
 	 *            least few kB.
+	 * @param curs
+	 *            temporary thread storage during data access.
 	 * @throws IOException
 	 *             when the object cannot be read.
 	 */
-	public void copyRawData(OutputStream out, byte buf[]) throws IOException {
-		pack.copyRawData(this, out, buf);
+	public void copyRawData(OutputStream out, byte buf[], WindowCursor curs)
+			throws IOException {
+		pack.copyRawData(this, out, buf, curs);
 	}
 
 	/**
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/WholePackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/WholePackedObjectLoader.java
index 3b4f90d..a1df3d2 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/WholePackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WholePackedObjectLoader.java
@@ -46,30 +46,33 @@
 class WholePackedObjectLoader extends PackedObjectLoader {
 	private static final int OBJ_COMMIT = Constants.OBJ_COMMIT;
 
-	WholePackedObjectLoader(final WindowCursor curs, final PackFile pr,
-			final long dataOffset, final long objectOffset, final int type,
-			final int size) {
-		super(curs, pr, dataOffset, objectOffset);
+	WholePackedObjectLoader(final PackFile pr, final long dataOffset,
+			final long objectOffset, final int type, final int size) {
+		super(pr, dataOffset, objectOffset);
 		objectType = type;
 		objectSize = size;
 	}
 
 	@Override
-	public byte[] getCachedBytes() throws IOException {
+	public void materialize(final WindowCursor curs) throws IOException {
+		if (cachedBytes != null) {
+			return;
+		}
+
 		if (objectType != OBJ_COMMIT) {
 			final UnpackedObjectCache.Entry cache = pack.readCache(dataOffset);
 			if (cache != null) {
 				curs.release();
-				return cache.data;
+				cachedBytes = cache.data;
+				return;
 			}
 		}
 
 		try {
-			final byte[] data = pack.decompress(dataOffset, objectSize, curs);
+			cachedBytes = pack.decompress(dataOffset, objectSize, curs);
 			curs.release();
 			if (objectType != OBJ_COMMIT)
-				pack.saveCache(dataOffset, data, objectType);
-			return data;
+				pack.saveCache(dataOffset, cachedBytes, objectType);
 		} catch (DataFormatException dfe) {
 			final CorruptObjectException coe;
 			coe = new CorruptObjectException("Object at " + dataOffset + " in "

diff --git a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ConcurrentRepackTest.java b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ConcurrentRepackTest.java
index 825fbb8..b56e0f4 100644
--- a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ConcurrentRepackTest.java
+++ b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ConcurrentRepackTest.java
@@ -41,6 +41,7 @@
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.util.Arrays;
 
 import org.spearce.jgit.errors.IncorrectObjectTypeException;
 import org.spearce.jgit.errors.MissingObjectException;
@@ -128,6 +129,45 @@ public void testObjectMovedWithinPack()
 		assertEquals(o2.name(), parse(o2).name());
 	}
 
+	public void testObjectMovedToNewPack2()
+			throws IncorrectObjectTypeException, IOException {
+		// Create an object and pack it. Then remove that pack and put the
+		// object into a different pack file, with some other object. We
+		// still should be able to access the objects.
+		//
+		final Repository eden = createNewEmptyRepo();
+		final RevObject o1 = writeBlob(eden, "o1");
+		final File[] out1 = pack(eden, o1);
+		assertEquals(o1.name(), parse(o1).name());
+
+		final ObjectLoader load1 = db.openBlob(o1);
+		assertNotNull(load1);
+
+		final RevObject o2 = writeBlob(eden, "o2");
+		pack(eden, o2, o1);
+
+		// Force close, and then delete, the old pack.
+		//
+		whackCache();
+		delete(out1);
+
+		// Now here is the interesting thing... can the loader we made
+		// earlier still resolve the object, even though its underlying
+		// pack is gone, but the object still exists.
+		//
+		final ObjectLoader load2 = db.openBlob(o1);
+		assertNotNull(load2);
+		assertNotSame(load1, load2);
+
+		final byte[] data2 = load2.getCachedBytes();
+		final byte[] data1 = load1.getCachedBytes();
+		assertNotNull(data2);
+		assertNotNull(data1);
+		assertNotSame(data1, data2); // cache should be per-pack, not per object
+		assertTrue(Arrays.equals(data1, data2));
+		assertEquals(load2.getType(), load1.getType());
+	}
+
 	private static void whackCache() {
 		final WindowCacheConfig config = new WindowCacheConfig();
 

org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java, org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java, org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
index e1397fd..2da8bbc 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackWriter.java
@@ -606,14 +606,7 @@ private void searchForReuse() throws IOException {
 					throw new IOException(
 							"Packing cancelled during objects writing");
 				reuseLoaders.clear();
-				db.openObjectInAllPacks(otp, reuseLoaders, windowCursor);
-				if (reuseDeltas) {
-					selectDeltaReuseForObject(otp, reuseLoaders);
-				}
-				// delta reuse is preferred over object reuse
-				if (reuseObjects && !otp.hasReuseLoader()) {
-					selectObjectReuseForObject(otp, reuseLoaders);
-				}
+				searchForReuse(reuseLoaders, otp);
 				initMonitor.update(1);
 			}
 		}
@@ -621,6 +614,19 @@ private void searchForReuse() throws IOException {
 		initMonitor.endTask();
 	}
 
+	private void searchForReuse(
+			final Collection<PackedObjectLoader> reuseLoaders,
+			final ObjectToPack otp) throws IOException {
+		db.openObjectInAllPacks(otp, reuseLoaders, windowCursor);
+		if (reuseDeltas) {
+			selectDeltaReuseForObject(otp, reuseLoaders);
+		}
+		// delta reuse is preferred over object reuse
+		if (reuseObjects && !otp.hasReuseLoader()) {
+			selectObjectReuseForObject(otp, reuseLoaders);
+		}
+	}
+
 	private void selectDeltaReuseForObject(final ObjectToPack otp,
 			final Collection<PackedObjectLoader> loaders) throws IOException {
 		PackedObjectLoader bestLoader = null;
@@ -707,40 +713,69 @@ private void writeObject(final ObjectToPack otp) throws IOException {
 
 		out.resetCRC32();
 		otp.setOffset(out.length());
-		if (otp.isDeltaRepresentation())
-			writeDeltaObject(otp);
-		else
-			writeWholeObject(otp);
+		
+		final PackedObjectLoader reuse = open(otp);
+		if (reuse != null) {
+			try {
+				if (otp.isDeltaRepresentation()) {
+					writeDeltaObjectReuse(otp, reuse);
+				} else {
+					writeObjectHeader(otp.getType(), reuse.getSize());
+					reuse.copyRawData(out, buf, windowCursor);
+				}
+			} finally {
+				reuse.endCopyRawData();
+			}
+		} else if (otp.isDeltaRepresentation()) {
+			throw new IOException("creating deltas is not implemented");
+		} else {
+			writeWholeObjectDeflate(otp);
+		}
 		otp.setCRC(out.getCRC32());
 
 		writeMonitor.update(1);
 	}
 
-	private void writeWholeObject(final ObjectToPack otp) throws IOException {
-		if (otp.hasReuseLoader()) {
-			final PackedObjectLoader loader = otp.getReuseLoader();
-			writeObjectHeader(otp.getType(), loader.getSize());
-			loader.copyRawData(out, buf, windowCursor);
-			otp.disposeLoader();
-		} else {
-			final ObjectLoader loader = db.openObject(windowCursor, otp);
-			final byte[] data = loader.getCachedBytes();
-			writeObjectHeader(otp.getType(), data.length);
-			deflater.reset();
-			deflater.setInput(data, 0, data.length);
-			deflater.finish();
-			do {
-				final int n = deflater.deflate(buf, 0, buf.length);
-				if (n > 0)
-					out.write(buf, 0, n);
-			} while (!deflater.finished());
-		}
-	}
-
-	private void writeDeltaObject(final ObjectToPack otp) throws IOException {
-		final PackedObjectLoader loader = otp.getReuseLoader();
+	private PackedObjectLoader open(final ObjectToPack otp) throws IOException {
+		for (;;) {
+			PackedObjectLoader reuse = otp.useLoader();
+			if (reuse == null) {
+				return null;
+			}
+
+			try {
+				reuse.beginCopyRawData();
+				return reuse;
+			} catch (IOException err) {
+				// The pack we found the object in originally is gone, or
+				// it has been overwritten with a different layout.
+				//
+				otp.clearDeltaBase();
+				searchForReuse(new ArrayList<PackedObjectLoader>(), otp);
+				continue;
+			}
+		}
+	}
+
+	private void writeWholeObjectDeflate(final ObjectToPack otp)
+			throws IOException {
+		final ObjectLoader loader = db.openObject(windowCursor, otp);
+		final byte[] data = loader.getCachedBytes();
+		writeObjectHeader(otp.getType(), data.length);
+		deflater.reset();
+		deflater.setInput(data, 0, data.length);
+		deflater.finish();
+		do {
+			final int n = deflater.deflate(buf, 0, buf.length);
+			if (n > 0)
+				out.write(buf, 0, n);
+		} while (!deflater.finished());
+	}
+
+	private void writeDeltaObjectReuse(final ObjectToPack otp,
+			final PackedObjectLoader reuse) throws IOException {
 		if (deltaBaseAsOffset && otp.getDeltaBase() != null) {
-			writeObjectHeader(Constants.OBJ_OFS_DELTA, loader.getRawSize());
+			writeObjectHeader(Constants.OBJ_OFS_DELTA, reuse.getRawSize());
 
 			final ObjectToPack deltaBase = otp.getDeltaBase();
 			long offsetDiff = otp.getOffset() - deltaBase.getOffset();
@@ -752,12 +787,11 @@ private void writeDeltaObject(final ObjectToPack otp) throws IOException {
 
 			out.write(buf, pos, buf.length - pos);
 		} else {
-			writeObjectHeader(Constants.OBJ_REF_DELTA, loader.getRawSize());
+			writeObjectHeader(Constants.OBJ_REF_DELTA, reuse.getRawSize());
 			otp.getDeltaBaseId().copyRawTo(buf, 0);
 			out.write(buf, 0, Constants.OBJECT_ID_LENGTH);
 		}
-		loader.copyRawData(out, buf, windowCursor);
-		otp.disposeLoader();
+		reuse.copyRawData(out, buf, windowCursor);
 	}
 
 	private void writeObjectHeader(final int objectType, long dataLength)
@@ -955,8 +989,10 @@ boolean isWritten() {
 			return getOffset() != 0;
 		}
 
-		PackedObjectLoader getReuseLoader() {
-			return reuseLoader;
+		PackedObjectLoader useLoader() {
+			final PackedObjectLoader r = reuseLoader;
+			reuseLoader = null;
+			return r;
 		}
 
 		boolean hasReuseLoader() {
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
index 60333e7..6066ba1 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
@@ -106,6 +106,30 @@ public final long getDataOffset() {
 	}
 
 	/**
+	 * Peg the pack file open to support data copying.
+	 * <p>
+	 * Applications trying to copy raw pack data should ensure the pack stays
+	 * open and available throughout the entire copy. To do that use:
+	 * 
+	 * <pre>
+	 * loader.beginCopyRawData();
+	 * try {
+	 * 	loader.copyRawData(out, tmpbuf, curs);
+	 * } finally {
+	 * 	loader.endCopyRawData();
+	 * }
+	 * </pre>
+	 * 
+	 * @throws IOException
+	 *             this loader contains stale information and cannot be used.
+	 *             The most likely cause is the underlying pack file has been
+	 *             deleted, and the object has moved to another pack file.
+	 */
+	public void beginCopyRawData() throws IOException {
+		WindowCache.pin(pack);
+	}
+
+	/**
 	 * Copy raw object representation from storage to provided output stream.
 	 * <p>
 	 * Copied data doesn't include object header. User must provide temporary
@@ -121,12 +145,18 @@ public final long getDataOffset() {
 	 *            temporary thread storage during data access.
 	 * @throws IOException
 	 *             when the object cannot be read.
+	 * @see #beginCopyRawData()
 	 */
 	public void copyRawData(OutputStream out, byte buf[], WindowCursor curs)
 			throws IOException {
 		pack.copyRawData(this, out, buf, curs);
 	}
 
+	/** Release resources after {@link #beginCopyRawData()}. */
+	public void endCopyRawData() {
+		WindowCache.unpin(pack);
+	}
+
 	/**
 	 * @return true if this loader is capable of fast raw-data copying basing on
 	 *         compressed data checksum; false if raw-data copying needs
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
index 03e531a..51d149c 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
@@ -223,6 +223,19 @@ public static final void get(final WindowCursor curs, final PackFile wp,
 		curs.window.ensureLoaded(curs.handle);
 	}
 
+	static synchronized final void pin(final PackFile wp) throws IOException {
+		if (++wp.openCount == 1) {
+			openFile(wp);
+		}
+	}
+
+	static synchronized final void unpin(final PackFile wp) {
+		if (--wp.openCount == 0) {
+			openFileCount--;
+			wp.cacheClose();
+		}
+	}
+
 	private static synchronized final void getImpl(final WindowCursor curs,
 			final PackFile wp, final long position) throws IOException {
 		final int id = (int) (position >> windowSizeShift);
@@ -241,27 +254,7 @@ private static synchronized final void getImpl(final WindowCursor curs,
 		}
 
 		if (wp.openCount == 0) {
-			try {
-				openFileCount++;
-				releaseMemory();
-				runClearedWindowQueue();
-				wp.openCount = 1;
-				wp.cacheOpen();
-			} catch (IOException ioe) {
-				openFileCount--;
-				wp.openCount = 0;
-				throw ioe;
-			} catch (RuntimeException ioe) {
-				openFileCount--;
-				wp.openCount = 0;
-				throw ioe;
-			} catch (Error ioe) {
-				openFileCount--;
-				wp.openCount = 0;
-				throw ioe;
-			} finally {
-				wp.openCount--;
-			}
+			openFile(wp);
 
 			// The cacheOpen may have mapped the window we are trying to
 			// map ourselves. Retrying the search ensures that does not
@@ -294,6 +287,30 @@ private static synchronized final void getImpl(final WindowCursor curs,
 		insertLRU(e);
 	}
 
+	private static void openFile(final PackFile wp) throws IOException {
+		try {
+			openFileCount++;
+			releaseMemory();
+			runClearedWindowQueue();
+			wp.openCount = 1;
+			wp.cacheOpen();
+		} catch (IOException ioe) {
+			openFileCount--;
+			wp.openCount = 0;
+			throw ioe;
+		} catch (RuntimeException ioe) {
+			openFileCount--;
+			wp.openCount = 0;
+			throw ioe;
+		} catch (Error ioe) {
+			openFileCount--;
+			wp.openCount = 0;
+			throw ioe;
+		} finally {
+			wp.openCount--;
+		}
+	}
+
 	static synchronized void markLoaded(final ByteWindow w) {
 		if (--w.provider.openCount == 0) {
 			openFileCount--;