[JGIT PATCH v2 00/11] WindowCache rewrite... with tests

[JGIT PATCH v2 00/11] WindowCache rewrite... with tests

[Shawn O. Pearce]

Actually, this is my entire outstanding patch set series.

1 and 2 should be trivial to apply.

3-6 should be fairly straightforward.

7 maybe we delay until later, but I don't think any applications
use that map type.

8 is pretty trivial, and is needed to prevent 9 from deadlocking.

9-11 is the rewrite of WindowCache, with new unit tests to get higher
levels of coverage in this section of the code.  Actually doing
better is really hard, as we'd need to cause thread race conditions
deep within critical sections.  The only way I can think to do that
is to add injection points where we can insert "evil other thread"
logic during the unit test, and rely on the JIT to compile them
out in normal application usage.  Ick.  Its also quite fragile.

Shawn O. Pearce (11):
  Fix more computation of integer average overflows
  Fix performance problem recently introduced to
    DeltaPackedObjectLoader
  Replace inefficient new String(String) constructor to silence
    FindBugs
  Replace inefficient new Long(long) constructor to silence FindBugs
  Change IndexPack to use ObjectIdSubclassMap instead of ObjectIdMap
  Use getCachedBytes in IndexPack to avoid an unnecessary copy
  Remove ObjectIdMap from the JGit library
  Don't use ByteWindows when checking pack file headers/footers
  Rewrite WindowCache to be easier to follow and maintain
  Add tests for WindowCache.reconfigure cases
  Add tests to increase coverage of WindowCache

 .../jgit/test/resources/all_packed_objects.txt     |   96 ++++
 .../org/spearce/jgit/lib/ConcurrentRepackTest.java |    4 -
 .../tst/org/spearce/jgit/lib/ObjectIdMapTest.java  |  103 ----
 .../org/spearce/jgit/lib/WindowCacheGetTest.java   |  143 ++++++
 .../jgit/lib/WindowCacheReconfigureTest.java       |  119 +++++
 .../src/org/spearce/jgit/lib/ByteArrayWindow.java  |   57 +--
 .../src/org/spearce/jgit/lib/ByteBufferWindow.java |   41 +-
 .../src/org/spearce/jgit/lib/ByteWindow.java       |   91 +---
 .../spearce/jgit/lib/DeltaPackedObjectLoader.java  |    1 +
 .../src/org/spearce/jgit/lib/ObjectIdMap.java      |  201 --------
 .../org/spearce/jgit/lib/ObjectIdSubclassMap.java  |   31 ++-
 .../src/org/spearce/jgit/lib/OffsetCache.java      |  534 ++++++++++++++++++++
 .../src/org/spearce/jgit/lib/PackFile.java         |  128 +++--
 .../src/org/spearce/jgit/lib/PackIndexV1.java      |    2 +-
 .../src/org/spearce/jgit/lib/PackIndexV2.java      |    6 +-
 .../org/spearce/jgit/lib/PackedObjectLoader.java   |   11 +-
 .../src/org/spearce/jgit/lib/RefDatabase.java      |    3 +-
 .../src/org/spearce/jgit/lib/WindowCache.java      |  424 +++++-----------
 .../src/org/spearce/jgit/lib/WindowCursor.java     |   42 +-
 .../src/org/spearce/jgit/transport/IndexPack.java  |  129 +++--
 .../src/org/spearce/jgit/transport/LongMap.java    |  152 ++++++
 org.spearce.jgit/src/org/spearce/jgit/util/NB.java |   32 ++
 22 files changed, 1465 insertions(+), 885 deletions(-)
 create mode 100644 org.spearce.jgit.test/tst-rsrc/org/spearce/jgit/test/resources/all_packed_objects.txt
 delete mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/ObjectIdMapTest.java
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheGetTest.java
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheReconfigureTest.java
 delete mode 100644 org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdMap.java
 create mode 100644 org.spearce.jgit/src/org/spearce/jgit/lib/OffsetCache.java
 create mode 100644 org.spearce.jgit/src/org/spearce/jgit/transport/LongMap.java

[JGIT PATCH 01/11] Fix more computation of integer average overflows

[Shawn O. Pearce]

In 1d99aaab8e364c6ad722437e43c77fd54e13b071 Matthias Sohn pointed
out that (low+high)/2 can overflow, so (low+high)>>>1 is a better
choice when the result will be used as an array index.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../src/org/spearce/jgit/lib/PackIndexV1.java      |    2 +-
 .../src/org/spearce/jgit/lib/PackIndexV2.java      |    6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV1.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV1.java
index fdaa094..0ad29e1 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV1.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV1.java
@@ -129,7 +129,7 @@ long findOffset(final AnyObjectId objId) {
 		int high = data.length / (4 + Constants.OBJECT_ID_LENGTH);
 		int low = 0;
 		do {
-			final int mid = (low + high) / 2;
+			final int mid = (low + high) >>> 1;
 			final int pos = ((4 + Constants.OBJECT_ID_LENGTH) * mid) + 4;
 			final int cmp = objId.compareTo(data, pos);
 			if (cmp < 0)
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV2.java b/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV2.java
index eb56ed9..b539547 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV2.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackIndexV2.java
@@ -108,7 +108,7 @@ PackIndexV2(final InputStream fd) throws IOException {
 
 			final int intNameLen = (int) nameLen;
 			final byte[] raw = new byte[intNameLen];
-			final int[] bin = new int[intNameLen >> 2];
+			final int[] bin = new int[intNameLen >>> 2];
 			NB.readFully(fd, raw, 0, raw.length);
 			for (int i = 0; i < bin.length; i++)
 				bin[i] = NB.decodeInt32(raw, i << 2);
@@ -212,12 +212,12 @@ boolean hasCRC32Support() {
 
 	private int binarySearchLevelTwo(final AnyObjectId objId, final int levelOne) {
 		final int[] data = names[levelOne];
-		int high = offset32[levelOne].length >> 2;
+		int high = offset32[levelOne].length >>> 2;
 		if (high == 0)
 			return -1;
 		int low = 0;
 		do {
-			final int mid = (low + high) >> 1;
+			final int mid = (low + high) >>> 1;
 			final int mid4 = mid << 2;
 			final int cmp;
 
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 02/11] Fix performance problem recently introduced to DeltaPackedObjectLoader

[Shawn O. Pearce]

In fe6c8248e1ed6bd9db76a8314103081a02d55393 ("Fully materialize an
ObjectLoader before returning it from ObjectDatabase") I missed a
crucial return call here in DeltaPackedObjectLoadeder.  That one
missing line caused cache hits in the UnpackedObjectCache to then
fall through and unpack the delta base, and apply the delta onto
it, ignoring the fact that we had a successful cache hit.

When packing and serving e.g. the Linux kernel repository this
resulted in a 10x increase in the number of WindowCache.get()
invocations we saw, as the UnpackedObjectCache was useless.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../spearce/jgit/lib/DeltaPackedObjectLoader.java  |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

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 8194d94..7d3f30d 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/DeltaPackedObjectLoader.java
@@ -69,6 +69,7 @@ public void materialize(final WindowCursor curs) throws IOException {
 				objectType = cache.type;
 				objectSize = cache.data.length;
 				cachedBytes = cache.data;
+				return;
 			}
 		}
 
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 03/11] Replace inefficient new String(String) constructor to silence FindBugs

[Shawn O. Pearce]

FindBugs keeps reporting that our usage of new String(String)
is not the most efficient way to construct a string.

http://thread.gmane.org/gmane.comp.version-control.git/113739/focus=113787
> I had a specific reason for forcing a new String object here.
>
> The line in question, p, is from the packed-refs file and
> contains the entire SHA-1 in hex form at the beginning of it.
> We've converted that into binary as an ObjectId, it uses 1/4 the
> space of the string portion.
>
> The Ref object, its ObjectId, and its name string, are going to be
> cached in a Map, probably long-term.  We're better off shedding the
> 80 bytes of memory used to hold the hex SHA-1 then risk substring()
> deciding its "faster" to reuse the char[] then to make a copy of it.

Another way to force this new unique String instance with its own
private char[] is to use a StringBuilder and append onto it the
ref name.  This shouldn't be a warning for FindBugs, but it would
accomplish the same goal of producing 1 clean copy, with no extra
transient temporary array.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
CC: Yann Simon <yann.simon.fr@gmail.com>
CC: Matthias Sohn <matthias.sohn@sap.com>
---

 Unchanged.

 .../src/org/spearce/jgit/lib/RefDatabase.java      |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/RefDatabase.java b/org.spearce.jgit/src/org/spearce/jgit/lib/RefDatabase.java
index 87f26bf..bccf2d0 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/RefDatabase.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/RefDatabase.java
@@ -447,7 +447,8 @@ private synchronized void refreshPackedRefs() {
 
 					final int sp = p.indexOf(' ');
 					final ObjectId id = ObjectId.fromString(p.substring(0, sp));
-					final String name = new String(p.substring(sp + 1));
+					final String name = new StringBuilder(p.length() - (sp + 1))
+							.append(p, sp + 1, p.length()).toString();
 					last = new Ref(Ref.Storage.PACKED, name, name, id);
 					newPackedRefs.put(last.getName(), last);
 				}
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 04/11] Replace inefficient new Long(long) constructor to silence FindBugs

[Shawn O. Pearce]

FindBugs keeps warning us that new Long(long) is inefficient because
it doesn't permit using cached values in the -128..127 range.

http://thread.gmane.org/gmane.comp.version-control.git/113738/focus=113785
> Why I box with new Long() over Long.valueOf():
>
>  The standard only requires -128..127 to be cached.  A JRE can
>  cache value outside of this range if it chooses, but long has a
>  huge range, its unlikely to cache much beyond this required region.
>
>  Most pack files are in the 10 MB...100+ MB range.  Most objects
>  take more than 100 bytes in a pack, even compressed delta encoded.
>  Thus any object after the first is going to have its offset outside
>  of the cached range.
>
>  In other words, why waste the CPU cycles on the "cached range
>  bounds check" when I'm always going to fail and allocate.  I might
>  as well just allocate
>
>  These sections of code are rather performance critical for the
>  indexing phase of a pack receive, on either side of a connection.
>  I need to shave even more instructions out of the critical paths,
>  as its not fast enough as-is.  Using new Long() is quicker than
>  using Long.valueOf(), so new Long() it is.

We now use a custom Map implementation which supports primitive long
as the hash key, rather than requiring boxing for java.util.HashMap.
This removes the issue FindBugs was identifying.

This version performs slightly better than before.
index-pack on linux-2.6:

  parent commit:  2m58.611s
  this commit  :  2m57.068s

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
CC: Yann Simon <yann.simon.fr@gmail.com>
CC: Matthias Sohn <matthias.sohn@sap.com>
---

 Unchanged.
 
 .../src/org/spearce/jgit/transport/IndexPack.java  |   12 +-
 .../src/org/spearce/jgit/transport/LongMap.java    |  152 ++++++++++++++++++++
 2 files changed, 157 insertions(+), 7 deletions(-)
 create mode 100644 org.spearce.jgit/src/org/spearce/jgit/transport/LongMap.java

diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
index e0e4855..59fdeae 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
@@ -47,7 +47,6 @@
 import java.security.MessageDigest;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.List;
 import java.util.zip.CRC32;
 import java.util.zip.DataFormatException;
@@ -163,7 +162,7 @@ public static IndexPack create(final Repository db, final InputStream is)
 
 	private ObjectIdMap<ArrayList<UnresolvedDelta>> baseById;
 
-	private HashMap<Long, ArrayList<UnresolvedDelta>> baseByPos;
+	private LongMap<ArrayList<UnresolvedDelta>> baseByPos;
 
 	private byte[] objectData;
 
@@ -303,7 +302,7 @@ public void index(final ProgressMonitor progress) throws IOException {
 
 				entries = new PackedObjectInfo[(int) objectCount];
 				baseById = new ObjectIdMap<ArrayList<UnresolvedDelta>>();
-				baseByPos = new HashMap<Long, ArrayList<UnresolvedDelta>>();
+				baseByPos = new LongMap<ArrayList<UnresolvedDelta>>();
 
 				progress.beginTask(PROGRESS_DOWNLOAD, (int) objectCount);
 				for (int done = 0; done < objectCount; done++) {
@@ -382,8 +381,7 @@ private void resolveDeltas(final ProgressMonitor progress)
 
 	private void resolveDeltas(final PackedObjectInfo oe) throws IOException {
 		final int oldCRC = oe.getCRC();
-		if (baseById.containsKey(oe)
-				|| baseByPos.containsKey(new Long(oe.getOffset())))
+		if (baseById.containsKey(oe) || baseByPos.containsKey(oe.getOffset()))
 			resolveDeltas(oe.getOffset(), oldCRC, Constants.OBJ_BAD, null, oe);
 	}
 
@@ -448,7 +446,7 @@ private void resolveDeltas(final long pos, final int oldCRC, int type,
 	private void resolveChildDeltas(final long pos, int type, byte[] data,
 			PackedObjectInfo oe) throws IOException {
 		final ArrayList<UnresolvedDelta> a = baseById.remove(oe);
-		final ArrayList<UnresolvedDelta> b = baseByPos.remove(new Long(pos));
+		final ArrayList<UnresolvedDelta> b = baseByPos.remove(pos);
 		int ai = 0, bi = 0;
 		if (a != null && b != null) {
 			while (ai < a.size() && bi < b.size()) {
@@ -679,7 +677,7 @@ private void indexOneObject() throws IOException {
 				ofs <<= 7;
 				ofs += (c & 127);
 			}
-			final Long base = new Long(pos - ofs);
+			final long base = pos - ofs;
 			ArrayList<UnresolvedDelta> r = baseByPos.get(base);
 			if (r == null) {
 				r = new ArrayList<UnresolvedDelta>(8);
diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/LongMap.java b/org.spearce.jgit/src/org/spearce/jgit/transport/LongMap.java
new file mode 100644
index 0000000..ac41f56
--- /dev/null
+++ b/org.spearce.jgit/src/org/spearce/jgit/transport/LongMap.java
@@ -0,0 +1,152 @@
+/*
+ * Copyright (C) 2009, Google Inc.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Git Development Community nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.spearce.jgit.transport;
+
+/**
+ * Simple Map<long,Object> helper for {@link IndexPack}.
+ *
+ * @param <V>
+ *            type of the value instance.
+ */
+final class LongMap<V> {
+	private static final float LOAD_FACTOR = 0.75f;
+
+	private Node<V>[] table;
+
+	/** Number of entries currently in the map. */
+	private int size;
+
+	/** Next {@link #size} to trigger a {@link #grow()}. */
+	private int growAt;
+
+	LongMap() {
+		table = createArray(64);
+		growAt = (int) (table.length * LOAD_FACTOR);
+	}
+
+	boolean containsKey(final long key) {
+		return get(key) != null;
+	}
+
+	V get(final long key) {
+		for (Node<V> n = table[index(key)]; n != null; n = n.next) {
+			if (n.key == key)
+				return n.value;
+		}
+		return null;
+	}
+
+	V remove(final long key) {
+		Node<V> n = table[index(key)];
+		Node<V> prior = null;
+		while (n != null) {
+			if (n.key == key) {
+				if (prior == null)
+					table[index(key)] = n.next;
+				else
+					prior.next = n.next;
+				size--;
+				return n.value;
+			}
+			prior = n;
+			n = n.next;
+		}
+		return null;
+	}
+
+	V put(final long key, final V value) {
+		for (Node<V> n = table[index(key)]; n != null; n = n.next) {
+			if (n.key == key) {
+				final V o = n.value;
+				n.value = value;
+				return o;
+			}
+		}
+
+		if (++size == growAt)
+			grow();
+		insert(new Node<V>(key, value));
+		return null;
+	}
+
+	private void insert(final Node<V> n) {
+		final int idx = index(n.key);
+		n.next = table[idx];
+		table[idx] = n;
+	}
+
+	private void grow() {
+		final Node<V>[] oldTable = table;
+		final int oldSize = table.length;
+
+		table = createArray(oldSize << 1);
+		growAt = (int) (table.length * LOAD_FACTOR);
+		for (int i = 0; i < oldSize; i++) {
+			Node<V> e = oldTable[i];
+			while (e != null) {
+				final Node<V> n = e.next;
+				insert(e);
+				e = n;
+			}
+		}
+	}
+
+	private final int index(final long key) {
+		int h = ((int) key) >>> 1;
+		h ^= (h >>> 20) ^ (h >>> 12);
+		return h & (table.length - 1);
+	}
+
+	@SuppressWarnings("unchecked")
+	private static final <V> Node<V>[] createArray(final int sz) {
+		return new Node[sz];
+	}
+
+	private static class Node<V> {
+		final long key;
+
+		V value;
+
+		Node<V> next;
+
+		Node(final long k, final V v) {
+			key = k;
+			value = v;
+		}
+	}
+}
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 05/11] Change IndexPack to use ObjectIdSubclassMap instead of ObjectIdMap

[Shawn O. Pearce]

The ObjectIdSubclassMap performs slightly better on average than the
ObjectIdMap, and uses a lot less memory as we don't need to allocate
a tree node per tracked object.

This reduces the memory footprint of IndexPack, by storing a linked
list of the UnresolvedDelta objects directly in each map, which is
slightly smaller than using an ArrayList inside of a TreeMap.

Performance is marginally faster, but we now can declare ObjectIdMap
to be fully deprecated and start removing it from the library.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../org/spearce/jgit/lib/ObjectIdSubclassMap.java  |   31 +++++-
 .../src/org/spearce/jgit/transport/IndexPack.java  |  123 +++++++++++++-------
 2 files changed, 109 insertions(+), 45 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdSubclassMap.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdSubclassMap.java
index 2a13204..bdacec4 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdSubclassMap.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdSubclassMap.java
@@ -37,6 +37,8 @@
 
 package org.spearce.jgit.lib;
 
+import java.util.Iterator;
+
 /**
  * Fast, efficient map specifically for {@link ObjectId} subclasses.
  * <p>
@@ -51,7 +53,7 @@
  * @param <V>
  *            type of subclass of ObjectId that will be stored in the map.
  */
-public class ObjectIdSubclassMap<V extends ObjectId> {
+public class ObjectIdSubclassMap<V extends ObjectId> implements Iterable<V> {
 	private int size;
 
 	private V[] obj_hash;
@@ -114,6 +116,33 @@ public int size() {
 		return size;
 	}
 
+	public Iterator<V> iterator() {
+		return new Iterator<V>() {
+			private int found;
+
+			private int i;
+
+			public boolean hasNext() {
+				return found < size;
+			}
+
+			public V next() {
+				while (i < obj_hash.length) {
+					final V v = obj_hash[i++];
+					if (v != null) {
+						found++;
+						return v;
+					}
+				}
+				throw new IllegalStateException();
+			}
+
+			public void remove() {
+				throw new UnsupportedOperationException();
+			}
+		};
+	}
+
 	private final int index(final AnyObjectId id) {
 		return (id.w1 >>> 1) % obj_hash.length;
 	}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
index 59fdeae..eecad9c 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
@@ -62,7 +62,7 @@
 import org.spearce.jgit.lib.MutableObjectId;
 import org.spearce.jgit.lib.ObjectChecker;
 import org.spearce.jgit.lib.ObjectId;
-import org.spearce.jgit.lib.ObjectIdMap;
+import org.spearce.jgit.lib.ObjectIdSubclassMap;
 import org.spearce.jgit.lib.ObjectLoader;
 import org.spearce.jgit.lib.PackIndexWriter;
 import org.spearce.jgit.lib.ProgressMonitor;
@@ -160,9 +160,9 @@ public static IndexPack create(final Repository db, final InputStream is)
 
 	private final CRC32 crc = new CRC32();
 
-	private ObjectIdMap<ArrayList<UnresolvedDelta>> baseById;
+	private ObjectIdSubclassMap<DeltaChain> baseById;
 
-	private LongMap<ArrayList<UnresolvedDelta>> baseByPos;
+	private LongMap<UnresolvedDelta> baseByPos;
 
 	private byte[] objectData;
 
@@ -301,8 +301,8 @@ public void index(final ProgressMonitor progress) throws IOException {
 				readPackHeader();
 
 				entries = new PackedObjectInfo[(int) objectCount];
-				baseById = new ObjectIdMap<ArrayList<UnresolvedDelta>>();
-				baseByPos = new LongMap<ArrayList<UnresolvedDelta>>();
+				baseById = new ObjectIdSubclassMap<DeltaChain>();
+				baseByPos = new LongMap<UnresolvedDelta>();
 
 				progress.beginTask(PROGRESS_DOWNLOAD, (int) objectCount);
 				for (int done = 0; done < objectCount; done++) {
@@ -381,7 +381,7 @@ private void resolveDeltas(final ProgressMonitor progress)
 
 	private void resolveDeltas(final PackedObjectInfo oe) throws IOException {
 		final int oldCRC = oe.getCRC();
-		if (baseById.containsKey(oe) || baseByPos.containsKey(oe.getOffset()))
+		if (baseById.get(oe) != null || baseByPos.containsKey(oe.getOffset()))
 			resolveDeltas(oe.getOffset(), oldCRC, Constants.OBJ_BAD, null, oe);
 	}
 
@@ -443,34 +443,45 @@ private void resolveDeltas(final long pos, final int oldCRC, int type,
 		resolveChildDeltas(pos, type, data, oe);
 	}
 
+	private UnresolvedDelta removeBaseById(final AnyObjectId id){
+		final DeltaChain d = baseById.get(id);
+		return d != null ? d.remove() : null;
+	}
+
+	private static UnresolvedDelta reverse(UnresolvedDelta c) {
+		UnresolvedDelta tail = null;
+		while (c != null) {
+			final UnresolvedDelta n = c.next;
+			c.next = tail;
+			tail = c;
+			c = n;
+		}
+		return tail;
+	}
+
 	private void resolveChildDeltas(final long pos, int type, byte[] data,
 			PackedObjectInfo oe) throws IOException {
-		final ArrayList<UnresolvedDelta> a = baseById.remove(oe);
-		final ArrayList<UnresolvedDelta> b = baseByPos.remove(pos);
-		int ai = 0, bi = 0;
-		if (a != null && b != null) {
-			while (ai < a.size() && bi < b.size()) {
-				final UnresolvedDelta ad = a.get(ai);
-				final UnresolvedDelta bd = b.get(bi);
-				if (ad.position < bd.position) {
-					resolveDeltas(ad.position, ad.crc, type, data, null);
-					ai++;
-				} else {
-					resolveDeltas(bd.position, bd.crc, type, data, null);
-					bi++;
-				}
+		UnresolvedDelta a = reverse(removeBaseById(oe));
+		UnresolvedDelta b = reverse(baseByPos.remove(pos));
+		while (a != null && b != null) {
+			if (a.position < b.position) {
+				resolveDeltas(a.position, a.crc, type, data, null);
+				a = a.next;
+			} else {
+				resolveDeltas(b.position, b.crc, type, data, null);
+				b = b.next;
 			}
 		}
-		if (a != null)
-			while (ai < a.size()) {
-				final UnresolvedDelta ad = a.get(ai++);
-				resolveDeltas(ad.position, ad.crc, type, data, null);
-			}
-		if (b != null)
-			while (bi < b.size()) {
-				final UnresolvedDelta bd = b.get(bi++);
-				resolveDeltas(bd.position, bd.crc, type, data, null);
-			}
+		resolveChildDeltaChain(type, data, a);
+		resolveChildDeltaChain(type, data, b);
+	}
+
+	private void resolveChildDeltaChain(final int type, final byte[] data,
+			UnresolvedDelta a) throws IOException {
+		while (a != null) {
+			resolveDeltas(a.position, a.crc, type, data, null);
+			a = a.next;
+		}
 	}
 
 	private void fixThinPack(final ProgressMonitor progress) throws IOException {
@@ -479,11 +490,16 @@ private void fixThinPack(final ProgressMonitor progress) throws IOException {
 		packDigest.reset();
 		originalEOF = packOut.length() - 20;
 		final Deflater def = new Deflater(Deflater.DEFAULT_COMPRESSION, false);
+		final List<DeltaChain> missing = new ArrayList<DeltaChain>(64);
 		long end = originalEOF;
-		for (final ObjectId baseId : new ArrayList<ObjectId>(baseById.keySet())) {
+		for (final DeltaChain baseId : baseById) {
+			if (baseId.head == null)
+				continue;
 			final ObjectLoader ldr = repo.openObject(readCurs, baseId);
-			if (ldr == null)
+			if (ldr == null) {
+				missing.add(baseId);
 				continue;
+			}
 			final byte[] data = ldr.getBytes();
 			final int typeCode = ldr.getType();
 			final PackedObjectInfo oe;
@@ -501,9 +517,9 @@ private void fixThinPack(final ProgressMonitor progress) throws IOException {
 		}
 		def.end();
 
-		if (!baseById.isEmpty()) {
-			final ObjectId need = baseById.keySet().iterator().next();
-			throw new MissingObjectException(need, "delta base");
+		for (final DeltaChain base : missing) {
+			if (base.head != null)
+				throw new MissingObjectException(base, "delta base");
 		}
 
 		fixHeaderFooter(packcsum, packDigest.digest());
@@ -678,13 +694,10 @@ private void indexOneObject() throws IOException {
 				ofs += (c & 127);
 			}
 			final long base = pos - ofs;
-			ArrayList<UnresolvedDelta> r = baseByPos.get(base);
-			if (r == null) {
-				r = new ArrayList<UnresolvedDelta>(8);
-				baseByPos.put(base, r);
-			}
+			final UnresolvedDelta n;
 			skipInflateFromInput(sz);
-			r.add(new UnresolvedDelta(pos, (int) crc.getValue()));
+			n = new UnresolvedDelta(pos, (int) crc.getValue());
+			n.next = baseByPos.put(base, n);
 			deltaCount++;
 			break;
 		}
@@ -693,10 +706,10 @@ private void indexOneObject() throws IOException {
 			crc.update(buf, c, 20);
 			final ObjectId base = ObjectId.fromRaw(buf, c);
 			use(20);
-			ArrayList<UnresolvedDelta> r = baseById.get(base);
+			DeltaChain r = baseById.get(base);
 			if (r == null) {
-				r = new ArrayList<UnresolvedDelta>(8);
-				baseById.put(base, r);
+				r = new DeltaChain(base);
+				baseById.add(r);
 			}
 			skipInflateFromInput(sz);
 			r.add(new UnresolvedDelta(pos, (int) crc.getValue()));
@@ -937,11 +950,33 @@ private static CorruptObjectException corrupt(final DataFormatException dfe) {
 				+ dfe.getMessage());
 	}
 
+	private static class DeltaChain extends ObjectId {
+		UnresolvedDelta head;
+
+		DeltaChain(final AnyObjectId id) {
+			super(id);
+		}
+
+		UnresolvedDelta remove() {
+			final UnresolvedDelta r = head;
+			if (r != null)
+				head = null;
+			return r;
+		}
+
+		void add(final UnresolvedDelta d) {
+			d.next = head;
+			head = d;
+		}
+	}
+
 	private static class UnresolvedDelta {
 		final long position;
 
 		final int crc;
 
+		UnresolvedDelta next;
+
 		UnresolvedDelta(final long headerOffset, final int crc32) {
 			position = headerOffset;
 			crc = crc32;
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 06/11] Use getCachedBytes in IndexPack to avoid an unnecessary copy

[Shawn O. Pearce]

This is deep within the library code, where we know we won't overwrite
the cached buffer for an object.  Using getCachedBytes saves a full
array copy while fixing a thin pack and appending whole objects.  The
extra copy isn't so much an issue of CPU time as it is about creating
unnecessary temporary garbage for the GC to clean up.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../src/org/spearce/jgit/transport/IndexPack.java  |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
index eecad9c..eeeae16 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/transport/IndexPack.java
@@ -500,7 +500,7 @@ private void fixThinPack(final ProgressMonitor progress) throws IOException {
 				missing.add(baseId);
 				continue;
 			}
-			final byte[] data = ldr.getBytes();
+			final byte[] data = ldr.getCachedBytes();
 			final int typeCode = ldr.getType();
 			final PackedObjectInfo oe;
 
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 07/11] Remove ObjectIdMap from the JGit library

[Shawn O. Pearce]

Nobody within the library uses it anymore.

Applications should consider ObjectIdSubclassMap, or just use a normal
JDK map type like HashMap or TreeMap.  In general ObjectIdSubclassMap
supports major map functionality, runs faster, and uses less memory for
the same sized data set.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../tst/org/spearce/jgit/lib/ObjectIdMapTest.java  |  103 ----------
 .../src/org/spearce/jgit/lib/ObjectIdMap.java      |  201 --------------------
 2 files changed, 0 insertions(+), 304 deletions(-)
 delete mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/ObjectIdMapTest.java
 delete mode 100644 org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdMap.java

diff --git a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ObjectIdMapTest.java b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ObjectIdMapTest.java
deleted file mode 100644
index f1c1c0c..0000000
--- a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/ObjectIdMapTest.java
+++ /dev/null
@@ -1,103 +0,0 @@
-/*
- * Copyright (C) 2008, Robin Rosenberg <robin.rosenberg@dewire.com>
- *
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or
- * without modification, are permitted provided that the following
- * conditions are met:
- *
- * - Redistributions of source code must retain the above copyright
- *   notice, this list of conditions and the following disclaimer.
- *
- * - Redistributions in binary form must reproduce the above
- *   copyright notice, this list of conditions and the following
- *   disclaimer in the documentation and/or other materials provided
- *   with the distribution.
- *
- * - Neither the name of the Git Development Community nor the
- *   names of its contributors may be used to endorse or promote
- *   products derived from this software without specific prior
- *   written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
- * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
- * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
- * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
- * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
- * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
- * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
- * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
- * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-package org.spearce.jgit.lib;
-
-import java.util.Arrays;
-import java.util.Collection;
-import java.util.Map;
-import java.util.TreeMap;
-
-import junit.framework.TestCase;
-
-/**
- * Test functionality of ObjectIdMap
- *
- * The reason this class exists is performance, but those figures
- * are hard to make stable.
- */
-public class ObjectIdMapTest extends TestCase {
-
-	ObjectId[] ids = new ObjectId[500];
-	
-	protected void setUp() throws Exception {
-		int b=0;
-		for (int i=0; i<ids.length; ++i) {
-			byte[] data = new byte[Constants.OBJECT_ID_LENGTH];
-			for (int j=0; j<Constants.OBJECT_ID_LENGTH; ++j)
-				data[j] = (byte) (b++^0xEE);
-			ids[i] = ObjectId.fromRaw(data);
-		}
-	}
-
-	protected void tearDown() throws Exception {
-		ids = null; // avoid out of memory
-	}
-
-	/**
-	 * Verify that ObjectIdMap and TreeMap functionally are equivalent.
-	 */
-	@SuppressWarnings("unchecked")
-	public void testFunc() {
-		Map treeMap = new TreeMap();
-		for (int i=0; i<ids.length/100; ++i)
-			treeMap.put(ids[i],ids[i]);
-		Map levelMapWithTree = new ObjectIdMap(new TreeMap());
-		for (int i=0; i<ids.length/100; ++i)
-			levelMapWithTree.put(ids[i],ids[i]);
-		
-		assertEquals(treeMap, levelMapWithTree);
-		assertEquals(treeMap.values(), levelMapWithTree.values());
-		assertEquals(treeMap.keySet(), levelMapWithTree.keySet());
-
-		treeMap.remove(ids[30]);
-		levelMapWithTree.remove(ids[30]);
-		assertFalse(treeMap.containsKey(ids[30]));
-		assertFalse(levelMapWithTree.containsKey(ids[30]));
-		assertEquals(treeMap.values(), levelMapWithTree.values());
-		assertEquals(treeMap.keySet(), levelMapWithTree.keySet());
-	}
-
-	void assertEquals(Collection a, Collection b) {
-		Object[] aa = a.toArray();
-		Object[] ba = b.toArray();
-		Arrays.sort(aa);
-		Arrays.sort(ba);
-		assertTrue(Arrays.equals(aa, ba));
-	}
-
-}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdMap.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdMap.java
deleted file mode 100644
index d5b4294..0000000
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ObjectIdMap.java
+++ /dev/null
@@ -1,201 +0,0 @@
-/*
- * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
- *
- * All rights reserved.
- *
- * Redistribution and use in source and binary forms, with or
- * without modification, are permitted provided that the following
- * conditions are met:
- *
- * - Redistributions of source code must retain the above copyright
- *   notice, this list of conditions and the following disclaimer.
- *
- * - Redistributions in binary form must reproduce the above
- *   copyright notice, this list of conditions and the following
- *   disclaimer in the documentation and/or other materials provided
- *   with the distribution.
- *
- * - Neither the name of the Git Development Community nor the
- *   names of its contributors may be used to endorse or promote
- *   products derived from this software without specific prior
- *   written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
- * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
- * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
- * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
- * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
- * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
- * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
- * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
- * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
- * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
- * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-package org.spearce.jgit.lib;
-
-import java.lang.reflect.InvocationTargetException;
-import java.lang.reflect.Method;
-import java.util.AbstractMap;
-import java.util.AbstractSet;
-import java.util.Iterator;
-import java.util.Map;
-import java.util.Set;
-import java.util.TreeMap;
-
-/**
- * Very much like a map, but specialized to partition the data on the first byte
- * of the key. This is about twice as fast. See test class.
- *
- * Inspiration is taken from the Git pack file format which uses this technique
- * to improve lookup performance.
- *
- * @param <V>
- *            The value we map ObjectId's to.
- *
- */
-public class ObjectIdMap<V> extends AbstractMap<ObjectId, V> {
-
-	@SuppressWarnings("unchecked")
-	final Map<ObjectId, V>[] level0 = new Map[256];
-	
-	/**
-	 * Construct an ObjectIdMap with an underlying TreeMap implementation
-	 */
-	public ObjectIdMap() {
-		this(new TreeMap());
-	}
-
-	/**
-	 * Construct an ObjectIdMap with the same underlying map implementation as
-	 * the provided example.
-	 *
-	 * @param sample
-	 */
-	@SuppressWarnings("unchecked")
-	public ObjectIdMap(Map sample) {
-		try {
-			Method m=sample.getClass().getMethod("clone", (Class[])null);
-			for (int i=0; i<256; ++i) {
-				level0[i] = (Map)m.invoke(sample, (Object[])null);
-			}
-		} catch (IllegalAccessException e) {
-			throw new IllegalArgumentException(e);
-		} catch (IllegalArgumentException e) {
-			throw new IllegalArgumentException(e);
-		} catch (InvocationTargetException e) {
-			throw new IllegalArgumentException(e);
-		} catch (SecurityException e) {
-			throw new IllegalArgumentException(e);
-		} catch (NoSuchMethodException e) {
-			throw new IllegalArgumentException(e);
-		}
-	}
-	
-	public void clear() {
-		for (int i=0; i<256; ++i)
-			level0[i].clear();
-	}
-
-	public boolean containsKey(Object key) {
-		return submap((ObjectId)key).containsKey(key);
-	}
-
-	private final Map<ObjectId, V> submap(ObjectId key) {
-		return level0[key.getFirstByte()];
-	}
-
-	public boolean containsValue(Object value) {
-		for (int i=0; i<256; ++i)
-			if (level0[i].containsValue(value))
-				return true;
-		return false;
-	}
-
-	private Set<Map.Entry<ObjectId, V>> entrySet =
-		new AbstractSet<Map.Entry<ObjectId, V>>() {
-
-			@Override
-			final public Iterator<Map.Entry<ObjectId, V>> iterator() {
-				return new Iterator<Entry<ObjectId,V>>() {
-					private int levelIndex;
-					private boolean hasNext;
-					private Iterator<Map.Entry<ObjectId, V>> levelIterator;
-					private Iterator<Map.Entry<ObjectId, V>> lastIterator;
-					{
-						step();
-					}
-					public boolean hasNext() {
-						return hasNext;
-					}
-					public java.util.Map.Entry<ObjectId, V> next() {
-						Entry<ObjectId, V> ret = levelIterator.next();
-						step();
-						return ret;
-					}
-					public void remove() {
-						lastIterator.remove();
-					}
-
-					private void step() {
-						hasNext = false;
-						lastIterator = levelIterator;
-						while ((levelIterator==null || !(hasNext=levelIterator.hasNext()))) {
-							if (levelIndex < level0.length)
-								levelIterator = level0[levelIndex++].entrySet().iterator();
-							else
-								break;
-						}
-					}
-				};
-			}
-
-			@Override
-			public int size() {
-				int ret=0;
-				for (int i=0; i<256; ++i)
-					ret += level0[i].size();
-				return ret;
-			}
-	};
-
-
-	public Set<Map.Entry<ObjectId, V>> entrySet() {
-		return entrySet;
-	}
-
-	public V get(Object key) {
-		return submap((ObjectId)key).get(key);
-	}
-
-	public boolean isEmpty() {
-		for (int i=0; i<256; ++i)
-			if (!level0[i].isEmpty())
-				return false;
-		return true;
-	}
-
-	public V put(ObjectId key, V value) {
-		return submap(key).put(key, value);
-	}
-
-	public void putAll(Map<? extends ObjectId, ? extends V> arg0) {
-		for (Map.Entry<? extends ObjectId, ? extends V> entry : arg0.entrySet()) {
-			final ObjectId k = entry.getKey();
-			final V v = entry.getValue();
-			put(k,v);
-		}
-	}
-
-	public V remove(Object key) {
-		return submap((ObjectId) key).remove(key);
-	}
-
-	public int size() {
-		return entrySet().size();
-	}
-
-}
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 08/11] Don't use ByteWindows when checking pack file headers/footers

[Shawn O. Pearce]

Its highly unlikely we need the 8 KiB surrounding the pack file header
or footer immediately after opening the pack file.  Reading those as
full blocks and registering them in the WindowCache is probably just
churning garbage through the cache.  Instead, read the header with a
single 12 byte read, and the footer with a single 20 byte read, and
bypass the cache altogether.

This nicely removes a deadlock condition we had previously where the
WindowCache was recursively calling itself during the pack file open,
and got stuck on its own locks.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 Unchanged.

 .../src/org/spearce/jgit/lib/PackFile.java         |    5 +--
 org.spearce.jgit/src/org/spearce/jgit/util/NB.java |   32 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

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 813ebc7..360442f 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
@@ -389,10 +389,9 @@ void allocWindow(final WindowCursor curs, final int windowId,
 
 	private void onOpenPack() throws IOException {
 		final PackIndex idx = idx();
-		final WindowCursor curs = new WindowCursor();
 		final byte[] buf = new byte[20];
 
-		readFully(0, buf, 0, 12, curs);
+		NB.readFully(fd.getChannel(), 0, buf, 0, 12);
 		if (RawParseUtils.match(buf, 0, Constants.PACK_SIGNATURE) != 4)
 			throw new IOException("Not a PACK file.");
 		final long vers = NB.decodeUInt32(buf, 4);
@@ -406,7 +405,7 @@ private void onOpenPack() throws IOException {
 					+ " index " + idx.getObjectCount()
 					+ ": " + getPackFile());
 
-		readFully(length - 20, buf, 0, 20, curs);
+		NB.readFully(fd.getChannel(), length - 20, buf, 0, 20);
 		if (!Arrays.equals(buf, idx.packChecksum))
 			throw new PackMismatchException("Pack checksum mismatch:"
 					+ " pack " + ObjectId.fromRaw(buf).name()
diff --git a/org.spearce.jgit/src/org/spearce/jgit/util/NB.java b/org.spearce.jgit/src/org/spearce/jgit/util/NB.java
index c65c6fa..032997f 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/util/NB.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/util/NB.java
@@ -40,6 +40,8 @@
 import java.io.EOFException;
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
 
 /** Conversion utilities for network byte order handling. */
 public final class NB {
@@ -71,6 +73,36 @@ public static void readFully(final InputStream fd, final byte[] dst,
 	}
 
 	/**
+	 * Read the entire byte array into memory, or throw an exception.
+	 *
+	 * @param fd
+	 *            file to read the data from.
+	 * @param pos
+	 *            position to read from the file at.
+	 * @param dst
+	 *            buffer that must be fully populated, [off, off+len).
+	 * @param off
+	 *            position within the buffer to start writing to.
+	 * @param len
+	 *            number of bytes that must be read.
+	 * @throws EOFException
+	 *             the stream ended before dst was fully populated.
+	 * @throws IOException
+	 *             there was an error reading from the stream.
+	 */
+	public static void readFully(final FileChannel fd, long pos,
+			final byte[] dst, int off, int len) throws IOException {
+		while (len > 0) {
+			final int r = fd.read(ByteBuffer.wrap(dst, off, len), pos);
+			if (r <= 0)
+				throw new EOFException("Short read of block.");
+			pos += r;
+			off += r;
+			len -= r;
+		}
+	}
+
+	/**
 	 * Skip an entire region of an input stream.
 	 * <p>
 	 * The input stream's position is moved forward by the number of requested
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH v2 09/11] Rewrite WindowCache to be easier to follow and maintain

[Shawn O. Pearce]

The integration of WindowCache, ByteWindow, PackFile and WindowCursor
was a spaghetti of code that was impossible for even the original
author (me) to follow.  Due to the way the responsibility for the
PackFile's open RandomAccessFile "fd" was distributed between these
four classes I could no longer prove to myself that the fd wouldn't
be closed while it was being accessed by another thread.

This rewrite generalizes most of the cache logic into a new class,
OffsetCache.  The hope is that we can later reuse this code to make
a rewrite of UnpackedObjectCache, which uses similiar caching rules
as WindowCache, but applies a different hash function.  That rewrite
is deferred to another change, but is anticipated by this one.

The new OffsetCache class uses the Java 5 atomic APIs to create a
much more concurrent hash table than we had before.  We can now
perform no-miss reads without taking any locks.  Reads that do
miss acquire a lock in order to prevent concurrent threads from
performing duplicate work loading the same window from disk,
however concurrent reads of different windows is still permitted.

Due to the more concurrent nature of the OffsetCache, it is now
possible for the cache to temporarily overshoot its resource limits.
This is a small temporary overshoot that is roughly bounded by the
number of concurrent threads operating against the same cache.

The API of the ByteWindow subclasses is now simplified by removing
the base class of SoftReference.  It was a horrible idea to pass
the byte[] or MappedByteBuffer down through the call stack when the
implementation knew what type it should be operating on.  We now
instead use a more traditional OO pattern of allowing the subclass
to directly specify its referent.

Responsibility for the RandomAccessFile "fd" within PackFile is now
strictly within PackFile.  Two open reference counts track how the
callers are using the fd, ensuring that the fd remains open, so long
as the caller has made the appropriate begin*() invocation prior
to data access.  One counter, beginWindowCache() is exclusively
for the ByteWindows created by WindowCache.  Another counter,
beginCopyRawData(), is exclusively for PackWriter's need to lock
the PackFile open while it performs object reuse.

To keep the code simple a WindowCache.reconfigure() now discards the
entire current cache, and creates a new one.  That invalidates every
open file, and every open ByteWindow, and forces them to load again.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 I squashed a lot of the follow-up patches into this one.  They were
 all bug fixes to code introduced in this change anyway.

 .../org/spearce/jgit/lib/ConcurrentRepackTest.java |    4 -
 .../src/org/spearce/jgit/lib/ByteArrayWindow.java  |   57 +--
 .../src/org/spearce/jgit/lib/ByteBufferWindow.java |   41 +-
 .../src/org/spearce/jgit/lib/ByteWindow.java       |   91 +---
 .../src/org/spearce/jgit/lib/OffsetCache.java      |  534 ++++++++++++++++++++
 .../src/org/spearce/jgit/lib/PackFile.java         |  123 +++--
 .../org/spearce/jgit/lib/PackedObjectLoader.java   |    4 +-
 .../src/org/spearce/jgit/lib/WindowCache.java      |  418 ++++------------
 .../src/org/spearce/jgit/lib/WindowCursor.java     |   42 +-
 9 files changed, 787 insertions(+), 527 deletions(-)
 create mode 100644 org.spearce.jgit/src/org/spearce/jgit/lib/OffsetCache.java

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 b56e0f4..fa6345e 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
@@ -170,10 +170,6 @@ public void testObjectMovedToNewPack2()
 
 	private static void whackCache() {
 		final WindowCacheConfig config = new WindowCacheConfig();
-
-		config.setPackedGitOpenFiles(0);
-		WindowCache.reconfigure(config);
-
 		config.setPackedGitOpenFiles(1);
 		WindowCache.reconfigure(config);
 	}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteArrayWindow.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteArrayWindow.java
index 5dc3d28..6b96b10 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteArrayWindow.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteArrayWindow.java
@@ -38,41 +38,29 @@
 
 package org.spearce.jgit.lib;
 
-import java.io.IOException;
-import java.nio.ByteBuffer;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
 /**
  * A {@link ByteWindow} with an underlying byte array for storage.
  */
-final class ByteArrayWindow extends ByteWindow<byte[]> {
-	boolean loaded;
+final class ByteArrayWindow extends ByteWindow {
+	private final byte[] array;
 
-	/**
-	 * Constructor for ByteWindow.
-	 * 
-	 * @param o
-	 *            the PackFile providing data access
-	 * @param p
-	 *            the file offset.
-	 * @param d
-	 *            an id provided by the PackFile. See
-	 *            {@link WindowCache#get(WindowCursor, PackFile, long)}.
-	 * @param b
-	 *            byte array for storage
-	 */
-	ByteArrayWindow(final PackFile o, final long p, final int d, final byte[] b) {
-		super(o, p, d, b, b.length);
+	ByteArrayWindow(final PackFile pack, final long o, final byte[] b) {
+		super(pack, o, b.length);
+		array = b;
 	}
 
-	int copy(final byte[] array, final int p, final byte[] b, final int o, int n) {
+	@Override
+	protected int copy(final int p, final byte[] b, final int o, int n) {
 		n = Math.min(array.length - p, n);
 		System.arraycopy(array, p, b, o, n);
 		return n;
 	}
 
-	int inflate(final byte[] array, final int pos, final byte[] b, int o,
+	@Override
+	protected int inflate(final int pos, final byte[] b, int o,
 			final Inflater inf) throws DataFormatException {
 		while (!inf.finished()) {
 			if (inf.needsInput()) {
@@ -86,7 +74,8 @@ int inflate(final byte[] array, final int pos, final byte[] b, int o,
 		return o;
 	}
 
-	void inflateVerify(final byte[] array, final int pos, final Inflater inf)
+	@Override
+	protected void inflateVerify(final int pos, final Inflater inf)
 			throws DataFormatException {
 		while (!inf.finished()) {
 			if (inf.needsInput()) {
@@ -98,26 +87,4 @@ void inflateVerify(final byte[] array, final int pos, final Inflater inf)
 		while (!inf.finished() && !inf.needsInput())
 			inf.inflate(verifyGarbageBuffer, 0, verifyGarbageBuffer.length);
 	}
-
-	void ensureLoaded(final byte[] array) {
-		boolean release = false;
-		try {
-			synchronized (this) {
-				if (!loaded) {
-					release = true;
-					try {
-						provider.fd.getChannel().read(ByteBuffer.wrap(array),
-								start);
-					} catch (IOException e) {
-						throw new RuntimeException("Cannot fault in window", e);
-					}
-					loaded = true;
-				}
-			}
-		} finally {
-			if (release) {
-				WindowCache.markLoaded(this);
-			}
-		}
-	}
-}
\ No newline at end of file
+}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteBufferWindow.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteBufferWindow.java
index 01956fd..f9de9b4 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteBufferWindow.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteBufferWindow.java
@@ -47,24 +47,16 @@
  *
  * @see ByteWindow
  */
-final class ByteBufferWindow extends ByteWindow<ByteBuffer> {
-	/**
-	 * Constructor.
-	 *
-	 * @See ByteWindow
-	 *
-	 * @param o The PackFile
-	 * @param p the file offset.
-	 * @param d Window id
-	 * @param b ByteBuffer storage
-	 */
-	ByteBufferWindow(final PackFile o, final long p, final int d,
-			final ByteBuffer b) {
-		super(o, p, d, b, b.capacity());
+final class ByteBufferWindow extends ByteWindow {
+	private final ByteBuffer buffer;
+
+	ByteBufferWindow(final PackFile pack, final long o, final ByteBuffer b) {
+		super(pack, o, b.capacity());
+		buffer = b;
 	}
 
-	final int copy(final ByteBuffer buffer, final int p, final byte[] b,
-			final int o, int n) {
+	@Override
+	protected int copy(final int p, final byte[] b, final int o, int n) {
 		final ByteBuffer s = buffer.slice();
 		s.position(p);
 		n = Math.min(s.remaining(), n);
@@ -72,9 +64,9 @@ final int copy(final ByteBuffer buffer, final int p, final byte[] b,
 		return n;
 	}
 
-	int inflate(final ByteBuffer buffer, final int pos, final byte[] b, int o,
-			final Inflater inf)
-			throws DataFormatException {
+	@Override
+	protected int inflate(final int pos, final byte[] b, int o,
+			final Inflater inf) throws DataFormatException {
 		final byte[] tmp = new byte[512];
 		final ByteBuffer s = buffer.slice();
 		s.position(pos);
@@ -91,8 +83,9 @@ int inflate(final ByteBuffer buffer, final int pos, final byte[] b, int o,
 		return o;
 	}
 
-	void inflateVerify(final ByteBuffer buffer, final int pos,
-			final Inflater inf) throws DataFormatException {
+	@Override
+	protected void inflateVerify(final int pos, final Inflater inf)
+			throws DataFormatException {
 		final byte[] tmp = new byte[512];
 		final ByteBuffer s = buffer.slice();
 		s.position(pos);
@@ -107,8 +100,4 @@ void inflateVerify(final ByteBuffer buffer, final int pos,
 		while (!inf.finished() && !inf.needsInput())
 			inf.inflate(verifyGarbageBuffer, 0, verifyGarbageBuffer.length);
 	}
-
-	void ensureLoaded(final ByteBuffer ref) {
-		// Do nothing.
-	}
-}
\ No newline at end of file
+}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteWindow.java b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteWindow.java
index 0d01fca..e0bda2d 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/ByteWindow.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/ByteWindow.java
@@ -38,8 +38,6 @@
 
 package org.spearce.jgit.lib;
 
-import java.lang.ref.ReferenceQueue;
-import java.lang.ref.SoftReference;
 import java.util.zip.DataFormatException;
 import java.util.zip.Inflater;
 
@@ -51,64 +49,31 @@
  * is very low and has paged part of this process out to disk. Therefore copying
  * bytes from a window is very inexpensive.
  * </p>
- * 
- * @param <T>
- *            type of object reference used to manage the window data.
  */
-abstract class ByteWindow<T> extends SoftReference<T> {
-	boolean sizeActive = true;
+abstract class ByteWindow {
+	protected final PackFile pack;
 
-	ByteWindow<?> chainNext;
+	protected final long start;
 
-	ByteWindow<?> lruPrev;
+	protected final long end;
 
-	ByteWindow<?> lruNext;
-
-	final PackFile provider;
-
-	final int id;
-
-	final int size;
-
-	final long start;
-
-	final long end;
+	protected ByteWindow(final PackFile p, final long s, final int n) {
+		pack = p;
+		start = s;
+		end = start + n;
+	}
 
-	/**
-	 * Constructor for ByteWindow.
-	 * 
-	 * @param o
-	 *            the PackFile providing data access
-	 * @param pos
-	 *            the position in the file the data comes from.
-	 * @param d
-	 *            an id provided by the PackFile. See
-	 *            {@link WindowCache#get(WindowCursor, PackFile, long)}.
-	 * @param ref
-	 *            the object value required to perform data access.
-	 * @param sz
-	 *            the total number of bytes in this window.
-	 */
-	@SuppressWarnings("unchecked")
-	ByteWindow(final PackFile o, final long pos, final int d, final T ref,
-			final int sz) {
-		super(ref, (ReferenceQueue<T>) WindowCache.clearedWindowQueue);
-		provider = o;
-		size = sz;
-		id = d;
-		start = pos;
-		end = start + size;
+	final int size() {
+		return (int) (end - start);
 	}
 
 	final boolean contains(final PackFile neededFile, final long neededPos) {
-		return provider == neededFile && start <= neededPos && neededPos < end;
+		return pack == neededFile && start <= neededPos && neededPos < end;
 	}
 
 	/**
 	 * Copy bytes from the window to a caller supplied buffer.
 	 * 
-	 * @param ref
-	 *            the object value required to perform data access.
 	 * @param pos
 	 *            offset within the file to start copying from.
 	 * @param dstbuf
@@ -123,15 +88,13 @@ final boolean contains(final PackFile neededFile, final long neededPos) {
 	 *         <code>cnt</code> if <code>cnt</code> exceeded the number of
 	 *         bytes available.
 	 */
-	final int copy(T ref, long pos, byte[] dstbuf, int dstoff, int cnt) {
-		return copy(ref, (int) (pos - start), dstbuf, dstoff, cnt);
+	final int copy(long pos, byte[] dstbuf, int dstoff, int cnt) {
+		return copy((int) (pos - start), dstbuf, dstoff, cnt);
 	}
 
 	/**
 	 * Copy bytes from the window to a caller supplied buffer.
 	 * 
-	 * @param ref
-	 *            the object value required to perform data access.
 	 * @param pos
 	 *            offset within the window to start copying from.
 	 * @param dstbuf
@@ -146,15 +109,13 @@ final int copy(T ref, long pos, byte[] dstbuf, int dstoff, int cnt) {
 	 *         <code>cnt</code> if <code>cnt</code> exceeded the number of
 	 *         bytes available.
 	 */
-	abstract int copy(T ref, int pos, byte[] dstbuf, int dstoff, int cnt);
+	protected abstract int copy(int pos, byte[] dstbuf, int dstoff, int cnt);
 
 	/**
 	 * Pump bytes into the supplied inflater as input.
 	 * 
-	 * @param ref
-	 *            the object value required to perform data access.
 	 * @param pos
-	 *            offset within the window to start supplying input from.
+	 *            offset within the file to start supplying input from.
 	 * @param dstbuf
 	 *            destination buffer the inflater should output decompressed
 	 *            data to.
@@ -174,16 +135,14 @@ final int copy(T ref, long pos, byte[] dstbuf, int dstoff, int cnt) {
 	 *             the inflater encountered an invalid chunk of data. Data
 	 *             stream corruption is likely.
 	 */
-	final int inflate(T ref, long pos, byte[] dstbuf, int dstoff, Inflater inf)
+	final int inflate(long pos, byte[] dstbuf, int dstoff, Inflater inf)
 			throws DataFormatException {
-		return inflate(ref, (int) (pos - start), dstbuf, dstoff, inf);
+		return inflate((int) (pos - start), dstbuf, dstoff, inf);
 	}
 
 	/**
 	 * Pump bytes into the supplied inflater as input.
 	 * 
-	 * @param ref
-	 *            the object value required to perform data access.
 	 * @param pos
 	 *            offset within the window to start supplying input from.
 	 * @param dstbuf
@@ -205,18 +164,16 @@ final int inflate(T ref, long pos, byte[] dstbuf, int dstoff, Inflater inf)
 	 *             the inflater encountered an invalid chunk of data. Data
 	 *             stream corruption is likely.
 	 */
-	abstract int inflate(T ref, int pos, byte[] dstbuf, int dstoff, Inflater inf)
-			throws DataFormatException;
+	protected abstract int inflate(int pos, byte[] dstbuf, int dstoff,
+			Inflater inf) throws DataFormatException;
 
 	protected static final byte[] verifyGarbageBuffer = new byte[2048];
 
-	final void inflateVerify(T ref, long pos, Inflater inf)
+	final void inflateVerify(final long pos, final Inflater inf)
 			throws DataFormatException {
-		inflateVerify(ref, (int) (pos - start), inf);
+		inflateVerify((int) (pos - start), inf);
 	}
 
-	abstract void inflateVerify(T ref, int pos, Inflater inf)
+	protected abstract void inflateVerify(int pos, Inflater inf)
 			throws DataFormatException;
-
-	abstract void ensureLoaded(T ref);
-}
\ No newline at end of file
+}
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/OffsetCache.java b/org.spearce.jgit/src/org/spearce/jgit/lib/OffsetCache.java
new file mode 100644
index 0000000..a1cd4be
--- /dev/null
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/OffsetCache.java
@@ -0,0 +1,534 @@
+/*
+ * Copyright (C) 2009, Google Inc.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Git Development Community nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.spearce.jgit.lib;
+
+import java.io.IOException;
+import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.AtomicReferenceArray;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Least frequently used cache for objects specified by PackFile positions.
+ * <p>
+ * This cache maps a <code>({@link PackFile},position)</code> tuple to an Object.
+ * <p>
+ * This cache is suitable for objects that are "relative expensive" to compute
+ * from the underlying PackFile, given some known position in that file.
+ * <p>
+ * Whenever a cache miss occurs, {@link #load(PackFile, long)} is invoked by
+ * exactly one thread for the given <code>(PackFile,position)</code> key tuple.
+ * This is ensured by an array of locks, with the tuple hashed to a lock
+ * instance.
+ * <p>
+ * During a miss, older entries are evicted from the cache so long as
+ * {@link #isFull()} returns true.
+ * <p>
+ * Its too expensive during object access to be 100% accurate with a least
+ * recently used (LRU) algorithm. Strictly ordering every read is a lot of
+ * overhead that typically doesn't yield a corresponding benefit to the
+ * application.
+ * <p>
+ * This cache implements a loose LRU policy by randomly picking a window
+ * comprised of roughly 10% of the cache, and evicting the oldest accessed entry
+ * within that window.
+ * <p>
+ * Entities created by the cache are held under SoftReferences, permitting the
+ * Java runtime's garbage collector to evict entries when heap memory gets low.
+ * Most JREs implement a loose least recently used algorithm for this eviction.
+ * <p>
+ * The internal hash table does not expand at runtime, instead it is fixed in
+ * size at cache creation time. The internal lock table used to gate load
+ * invocations is also fixed in size.
+ * <p>
+ * The key tuple is passed through to methods as a pair of parameters rather
+ * than as a single Object, thus reducing the transient memory allocations of
+ * callers. It is more efficient to avoid the allocation, as we can't be 100%
+ * sure that a JIT would be able to stack-allocate a key tuple.
+ * <p>
+ * This cache has an implementation rule such that:
+ * <ul>
+ * <li>{@link #load(PackFile, long)} is invoked by at most one thread at a time
+ * for a given <code>(PackFile,position)</code> tuple.</li>
+ * <li>For every <code>load()</code> invocation there is exactly one
+ * {@link #createRef(PackFile, long, Object)} invocation to wrap a SoftReference
+ * around the cached entity.</li>
+ * <li>For every Reference created by <code>createRef()</code> there will be
+ * exactly one call to {@link #clear(Ref)} to cleanup any resources associated
+ * with the (now expired) cached entity.</li>
+ * </ul>
+ * <p>
+ * Therefore, it is safe to perform resource accounting increments during the
+ * {@link #load(PackFile, long)} or {@link #createRef(PackFile, long, Object)}
+ * methods, and matching decrements during {@link #clear(Ref)}. Implementors may
+ * need to override {@link #createRef(PackFile, long, Object)} in order to embed
+ * additional accounting information into an implementation specific
+ * {@link OffsetCache.Ref} subclass, as the cached entity may have already been
+ * evicted by the JRE's garbage collector.
+ * <p>
+ * To maintain higher concurrency workloads, during eviction only one thread
+ * performs the eviction work, while other threads can continue to insert new
+ * objects in parallel. This means that the cache can be temporarily over limit,
+ * especially if the nominated eviction thread is being starved relative to the
+ * other threads.
+ *
+ * @param <V>
+ *            type of value stored in the cache.
+ * @param <R>
+ *            type of {@link OffsetCache.Ref} subclass used by the cache.
+ */
+abstract class OffsetCache<V, R extends OffsetCache.Ref<V>> {
+	private static final Random rng = new Random();
+
+	/** ReferenceQueue that {@link #createRef(PackFile, long, Object)} must use. */
+	protected final ReferenceQueue<V> queue;
+
+	/** Number of entries in {@link #table}. */
+	private final int tableSize;
+
+	/** Access clock for loose LRU. */
+	private final AtomicLong clock;
+
+	/** Hash bucket directory; entries are chained below. */
+	private final AtomicReferenceArray<Entry<V>> table;
+
+	/** Locks to prevent concurrent loads for same (PackFile,position). */
+	private final Lock[] locks;
+
+	/** Lock to elect the eviction thread after a load occurs. */
+	private final ReentrantLock evictLock;
+
+	/** Number of {@link #table} buckets to scan for an eviction window. */
+	private final int evictBatch;
+
+	/**
+	 * Create a new cache with a fixed size entry table and lock table.
+	 *
+	 * @param tSize
+	 *            number of entries in the entry hash table.
+	 * @param lockCount
+	 *            number of entries in the lock table. This is the maximum
+	 *            concurrency rate for creation of new objects through
+	 *            {@link #load(PackFile, long)} invocations.
+	 */
+	OffsetCache(final int tSize, final int lockCount) {
+		if (tSize < 1)
+			throw new IllegalArgumentException("tSize must be >= 1");
+		if (lockCount < 1)
+			throw new IllegalArgumentException("lockCount must be >= 1");
+
+		queue = new ReferenceQueue<V>();
+		tableSize = tSize;
+		clock = new AtomicLong(1);
+		table = new AtomicReferenceArray<Entry<V>>(tableSize);
+		locks = new Lock[lockCount];
+		for (int i = 0; i < locks.length; i++)
+			locks[i] = new Lock();
+		evictLock = new ReentrantLock();
+
+		int eb = (int) (tableSize * .1);
+		if (64 < eb)
+			eb = 64;
+		else if (eb < 4)
+			eb = 4;
+		if (tableSize < eb)
+			eb = tableSize;
+		evictBatch = eb;
+	}
+
+	/**
+	 * Lookup a cached object, creating and loading it if it doesn't exist.
+	 *
+	 * @param pack
+	 *            the pack that "contains" the cached object.
+	 * @param position
+	 *            offset within <code>pack</code> of the object.
+	 * @return the object reference.
+	 * @throws IOException
+	 *             the object reference was not in the cache and could not be
+	 *             obtained by {@link #load(PackFile, long)}.
+	 */
+	V getOrLoad(final PackFile pack, final long position) throws IOException {
+		final int slot = slot(pack, position);
+		final Entry<V> e1 = table.get(slot);
+		V v = scan(e1, pack, position);
+		if (v != null)
+			return v;
+
+		synchronized (lock(pack, position)) {
+			Entry<V> e2 = table.get(slot);
+			if (e2 != e1) {
+				v = scan(e2, pack, position);
+				if (v != null)
+					return v;
+			}
+
+			v = load(pack, position);
+			final Ref<V> ref = createRef(pack, position, v);
+			hit(ref);
+			for (;;) {
+				final Entry<V> n = new Entry<V>(clean(e2), ref);
+				if (table.compareAndSet(slot, e2, n))
+					break;
+				e2 = table.get(slot);
+			}
+		}
+
+		if (evictLock.tryLock()) {
+			try {
+				gc();
+				evict();
+			} finally {
+				evictLock.unlock();
+			}
+		}
+
+		return v;
+	}
+
+	private V scan(Entry<V> n, final PackFile pack, final long position) {
+		for (; n != null; n = n.next) {
+			final Ref<V> r = n.ref;
+			if (r.pack == pack && r.position == position) {
+				final V v = r.get();
+				if (v != null) {
+					hit(r);
+					return v;
+				}
+				n.kill();
+				break;
+			}
+		}
+		return null;
+	}
+
+	private void hit(final Ref<V> r) {
+		// We don't need to be 100% accurate here. Its sufficient that at least
+		// one thread performs the increment. Any other concurrent access at
+		// exactly the same time can simply use the same clock value.
+		//
+		// Consequently we attempt the set, but we don't try to recover should
+		// it fail. This is why we don't use getAndIncrement() here.
+		//
+		final long c = clock.get();
+		clock.compareAndSet(c, c + 1);
+		r.lastAccess = c;
+	}
+
+	private void evict() {
+		final int start = rng.nextInt(tableSize);
+		int ptr = start;
+		while (isFull()) {
+			Entry<V> old = null;
+			int slot = 0;
+			for (int b = evictBatch - 1; b >= 0; b--) {
+				if (tableSize <= ptr)
+					ptr = 0;
+				for (Entry<V> e = table.get(ptr); e != null; e = e.next) {
+					if (e.dead)
+						continue;
+					if (old == null || e.ref.lastAccess < old.ref.lastAccess) {
+						old = e;
+						slot = ptr;
+					}
+				}
+				if (++ptr == start)
+					return;
+			}
+			if (old != null) {
+				old.kill();
+				gc();
+				final Entry<V> e1 = table.get(slot);
+				table.compareAndSet(slot, e1, clean(e1));
+			}
+		}
+	}
+
+	/**
+	 * Clear every entry from the cache.
+	 *<p>
+	 * This is a last-ditch effort to clear out the cache, such as before it
+	 * gets replaced by another cache that is configured differently. This
+	 * method tries to force every cached entry through {@link #clear(Ref)} to
+	 * ensure that resources are correctly accounted for and cleaned up by the
+	 * subclass. A concurrent reader loading entries while this method is
+	 * running may cause resource accounting failures.
+	 */
+	void removeAll() {
+		for (int s = 0; s < tableSize; s++) {
+			Entry<V> e1;
+			do {
+				e1 = table.get(s);
+				for (Entry<V> e = e1; e != null; e = e.next)
+					e.kill();
+			} while (!table.compareAndSet(s, e1, null));
+		}
+		gc();
+	}
+
+	/**
+	 * Clear all entries related to a single file.
+	 * <p>
+	 * Typically this method is invoked during {@link PackFile#close()}, when we
+	 * know the pack is never going to be useful to us again (for example, it no
+	 * longer exists on disk). A concurrent reader loading an entry from this
+	 * same pack may cause the pack to become stuck in the cache anyway.
+	 *
+	 * @param pack
+	 *            the file to purge all entries of.
+	 */
+	void removeAll(final PackFile pack) {
+		for (int s = 0; s < tableSize; s++) {
+			final Entry<V> e1 = table.get(s);
+			boolean hasDead = false;
+			for (Entry<V> e = e1; e != null; e = e.next) {
+				if (e.ref.pack == pack) {
+					e.kill();
+					hasDead = true;
+				} else if (e.dead)
+					hasDead = true;
+			}
+			if (hasDead)
+				table.compareAndSet(s, e1, clean(e1));
+		}
+		gc();
+	}
+
+	/**
+	 * Materialize an object that doesn't yet exist in the cache.
+	 * <p>
+	 * This method is invoked by {@link #getOrLoad(PackFile, long)} when the
+	 * specified entity does not yet exist in the cache. Internal locking
+	 * ensures that at most one thread can call this method for each unique
+	 * <code>(pack,position)</code>, but multiple threads can call this method
+	 * concurrently for different <code>(pack,position)</code> tuples.
+	 *
+	 * @param pack
+	 *            the file to materialize the entry from.
+	 * @param position
+	 *            offset within the file of the entry.
+	 * @return the materialized object. Must never be null.
+	 * @throws IOException
+	 *             the method was unable to materialize the object for this
+	 *             input pair. The usual reasons would be file corruption, file
+	 *             not found, out of file descriptors, etc.
+	 */
+	protected abstract V load(PackFile pack, long position) throws IOException;
+
+	/**
+	 * Construct a Ref (SoftReference) around a cached entity.
+	 * <p>
+	 * Implementing this is only necessary if the subclass is performing
+	 * resource accounting during {@link #load(PackFile, long)} and
+	 * {@link #clear(Ref)} requires some information to update the accounting.
+	 * <p>
+	 * Implementors <b>MUST</b> ensure that the returned reference uses the
+	 * {@link #queue} ReferenceQueue, otherwise {@link #clear(Ref)} will not be
+	 * invoked at the proper time.
+	 *
+	 * @param pack
+	 *            the file to materialize the entry from.
+	 * @param position
+	 *            offset within the file of the entry.
+	 * @param v
+	 *            the object returned by {@link #load(PackFile, long)}.
+	 * @return a soft reference subclass wrapped around <code>v</code>.
+	 */
+	@SuppressWarnings("unchecked")
+	protected R createRef(final PackFile pack, final long position, final V v) {
+		return (R) new Ref<V>(pack, position, v, queue);
+	}
+
+	/**
+	 * Update accounting information now that an object has left the cache.
+	 * <p>
+	 * This method is invoked exactly once for the combined
+	 * {@link #load(PackFile, long)} and
+	 * {@link #createRef(PackFile, long, Object)} invocation pair that was used
+	 * to construct and insert an object into the cache.
+	 *
+	 * @param ref
+	 *            the reference wrapped around the object. Implementations must
+	 *            be prepared for <code>ref.get()</code> to return null.
+	 */
+	protected void clear(final R ref) {
+		// Do nothing by default.
+	}
+
+	/**
+	 * Determine if the cache is full and requires eviction of entries.
+	 * <p>
+	 * By default this method returns false. Implementors may override to
+	 * consult with the accounting updated by {@link #load(PackFile, long)},
+	 * {@link #createRef(PackFile, long, Object)} and {@link #clear(Ref)}.
+	 *
+	 * @return true if the cache is still over-limit and requires eviction of
+	 *         more entries.
+	 */
+	protected boolean isFull() {
+		return false;
+	}
+
+	@SuppressWarnings("unchecked")
+	private void gc() {
+		R r;
+		while ((r = (R) queue.poll()) != null) {
+			// Sun's Java 5 and 6 implementation have a bug where a Reference
+			// can be enqueued and dequeued twice on the same reference queue
+			// due to a race condition within ReferenceQueue.enqueue(Reference).
+			//
+			// We CANNOT permit a Reference to come through us twice, as it will
+			// skew the resource counters we maintain. Our canClear() check here
+			// provides a way to skip the redundant dequeues, if any.
+			//
+			if (r.canClear()) {
+				clear(r);
+
+				boolean found = false;
+				final int s = slot(r.pack, r.position);
+				final Entry<V> e1 = table.get(s);
+				for (Entry<V> n = e1; n != null; n = n.next) {
+					if (n.ref == r) {
+						n.dead = true;
+						found = true;
+						break;
+					}
+				}
+				if (found)
+					table.compareAndSet(s, e1, clean(e1));
+			}
+		}
+	}
+
+	/**
+	 * Compute the hash code value for a <code>(PackFile,position)</code> tuple.
+	 * <p>
+	 * For example, <code>return packHash + (int) (position >>> 4)</code>.
+	 * Implementors must override with a suitable hash (for example, a different
+	 * right shift on the position).
+	 *
+	 * @param packHash
+	 *            hash code for the file being accessed.
+	 * @param position
+	 *            position within the file being accessed.
+	 * @return a reasonable hash code mixing the two values.
+	 */
+	protected abstract int hash(int packHash, long position);
+
+	private int slot(final PackFile pack, final long position) {
+		return (hash(pack.hash, position) >>> 1) % tableSize;
+	}
+
+	private Lock lock(final PackFile pack, final long position) {
+		return locks[(hash(pack.hash, position) >>> 1) % locks.length];
+	}
+
+	private static <V> Entry<V> clean(Entry<V> top) {
+		while (top != null && top.dead) {
+			top.ref.enqueue();
+			top = top.next;
+		}
+		if (top == null)
+			return null;
+		final Entry<V> n = clean(top.next);
+		return n == top.next ? top : new Entry<V>(n, top.ref);
+	}
+
+	private static class Entry<V> {
+		/** Next entry in the hash table's chain list. */
+		final Entry<V> next;
+
+		/** The referenced object. */
+		final Ref<V> ref;
+
+		/**
+		 * Marked true when ref.get() returns null and the ref is dead.
+		 * <p>
+		 * A true here indicates that the ref is no longer accessible, and that
+		 * we therefore need to eventually purge this Entry object out of the
+		 * bucket's chain.
+		 */
+		volatile boolean dead;
+
+		Entry(final Entry<V> n, final Ref<V> r) {
+			next = n;
+			ref = r;
+		}
+
+		final void kill() {
+			dead = true;
+			ref.enqueue();
+		}
+	}
+
+	/**
+	 * A soft reference wrapped around a cached object.
+	 *
+	 * @param <V>
+	 *            type of the cached object.
+	 */
+	protected static class Ref<V> extends SoftReference<V> {
+		final PackFile pack;
+
+		final long position;
+
+		long lastAccess;
+
+		private boolean cleared;
+
+		protected Ref(final PackFile pack, final long position, final V v,
+				final ReferenceQueue<V> queue) {
+			super(v, queue);
+			this.pack = pack;
+			this.position = position;
+		}
+
+		final synchronized boolean canClear() {
+			if (cleared)
+				return false;
+			cleared = true;
+			return true;
+		}
+	}
+
+	private static final class Lock {
+		// Used only for its implicit monitor.
+	}
+}
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 360442f..b107dfe 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackFile.java
@@ -77,12 +77,13 @@ public int compare(final PackFile a, final PackFile b) {
 
 	final int hash;
 
-	RandomAccessFile fd;
+	private RandomAccessFile fd;
 
 	long length;
 
-	/** Total number of windows actively in the associated cache. */
-	int openCount;
+	private int activeWindows;
+
+	private int activeCopyRawData;
 
 	private int packLastModified;
 
@@ -310,27 +311,57 @@ private void copyToStream(long position, final byte[] buf, long cnt,
 		}
 	}
 
-	void cacheOpen() throws IOException {
-		fd = new RandomAccessFile(packFile, "r");
-		length = fd.length();
+	synchronized void beginCopyRawData() throws IOException {
+		if (++activeCopyRawData == 1 && activeWindows == 0)
+			doOpen();
+	}
+
+	synchronized void endCopyRawData() {
+		if (--activeCopyRawData == 0 && activeWindows == 0)
+			doClose();
+	}
+
+	synchronized boolean beginWindowCache() throws IOException {
+		if (++activeWindows == 1) {
+			if (activeCopyRawData == 0)
+				doOpen();
+			return true;
+		}
+		return false;
+	}
+
+	synchronized boolean endWindowCache() {
+		final boolean r = --activeWindows == 0;
+		if (r && activeCopyRawData == 0)
+			doClose();
+		return r;
+	}
+
+	private void doOpen() throws IOException {
 		try {
+			fd = new RandomAccessFile(packFile, "r");
+			length = fd.length();
 			onOpenPack();
 		} catch (IOException ioe) {
-			invalid = true;
-			cacheClose();
+			openFail();
 			throw ioe;
 		} catch (RuntimeException re) {
-			invalid = true;
-			cacheClose();
+			openFail();
 			throw re;
 		} catch (Error re) {
-			invalid = true;
-			cacheClose();
+			openFail();
 			throw re;
 		}
 	}
 
-	void cacheClose() {
+	private void openFail() {
+		activeWindows = 0;
+		activeCopyRawData = 0;
+		invalid = true;
+		doClose();
+	}
+
+	private void doClose() {
 		if (fd != null) {
 			try {
 				fd.close();
@@ -343,48 +374,34 @@ void cacheClose() {
 		}
 	}
 
-	void allocWindow(final WindowCursor curs, final int windowId,
-			final long pos, final int size) {
-		if (WindowCache.mmap) {
-			MappedByteBuffer map;
-			try {
-				map = fd.getChannel().map(MapMode.READ_ONLY, pos, size);
-			} catch (IOException e) {
-				// The most likely reason this failed is the JVM has run out
-				// of virtual memory. We need to discard quickly, and try to
-				// force the GC to finalize and release any existing mappings.
-				try {
-					curs.release();
-					System.gc();
-					System.runFinalization();
-					map = fd.getChannel().map(MapMode.READ_ONLY, pos, size);
-				} catch (IOException ioe2) {
-					// Temporarily disable mmap and do buffered disk IO.
-					//
-					map = null;
-					System.err.println("warning: mmap failure: "+ioe2);
-				}
-			}
-			if (map != null) {
-				if (map.hasArray()) {
-					final byte[] b = map.array();
-					final ByteArrayWindow w;
-					w = new ByteArrayWindow(this, pos, windowId, b);
-					w.loaded = true;
-					curs.window = w;
-					curs.handle = b;
-				} else {
-					curs.window = new ByteBufferWindow(this, pos, windowId, map);
-					curs.handle = map;
-				}
-				return;
-			}
+	ByteArrayWindow read(final long pos, int size) throws IOException {
+		if (length < pos + size)
+			size = (int) (length - pos);
+		final byte[] buf = new byte[size];
+		NB.readFully(fd.getChannel(), pos, buf, 0, size);
+		return new ByteArrayWindow(this, pos, buf);
+	}
+
+	ByteWindow mmap(final long pos, int size) throws IOException {
+		if (length < pos + size)
+			size = (int) (length - pos);
+
+		MappedByteBuffer map;
+		try {
+			map = fd.getChannel().map(MapMode.READ_ONLY, pos, size);
+		} catch (IOException ioe1) {
+			// The most likely reason this failed is the JVM has run out
+			// of virtual memory. We need to discard quickly, and try to
+			// force the GC to finalize and release any existing mappings.
+			//
+			System.gc();
+			System.runFinalization();
+			map = fd.getChannel().map(MapMode.READ_ONLY, pos, size);
 		}
 
-		final byte[] b = new byte[size];
-		curs.window = new ByteArrayWindow(this, pos, windowId, b);
-		curs.handle = b;
-		openCount++; // Until the window loads, we must stay open.
+		if (map.hasArray())
+			return new ByteArrayWindow(this, pos, map.array());
+		return new ByteBufferWindow(this, pos, map);
 	}
 
 	private void onOpenPack() throws IOException {
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 d49562a..0c3e783 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
@@ -126,7 +126,7 @@ public final long getDataOffset() {
 	 *             deleted, and the object has moved to another pack file.
 	 */
 	public void beginCopyRawData() throws IOException {
-		WindowCache.pin(pack);
+		pack.beginCopyRawData();
 	}
 
 	/**
@@ -154,7 +154,7 @@ public void copyRawData(OutputStream out, byte buf[], WindowCursor curs)
 
 	/** Release resources after {@link #beginCopyRawData()}. */
 	public void endCopyRawData() {
-		WindowCache.unpin(pack);
+		pack.endCopyRawData();
 	}
 
 	/**
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 51d149c..0102a2d 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
@@ -40,12 +40,17 @@
 
 import java.io.IOException;
 import java.lang.ref.ReferenceQueue;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /**
- * The WindowCache manages reusable <code>Windows</code> and inflaters used by
- * the other windowed file access classes.
+ * Caches slices of a {@link PackFile} in memory for faster read access.
+ * <p>
+ * The WindowCache serves as a Java based "buffer cache", loading segments of a
+ * PackFile into the JVM heap prior to use. As JGit often wants to do reads of
+ * only tiny slices of a file, the WindowCache tries to smooth out these tiny
+ * reads into larger block-sized IO operations.
  */
-public class WindowCache {
+public class WindowCache extends OffsetCache<ByteWindow, WindowCache.WindowRef> {
 	private static final int bits(int newSize) {
 		if (newSize < 4096)
 			throw new IllegalArgumentException("Invalid window size");
@@ -54,41 +59,10 @@ private static final int bits(int newSize) {
 		return Integer.numberOfTrailingZeros(newSize);
 	}
 
-	private static int maxFileCount;
-
-	private static int maxByteCount;
-
-	private static int windowSize;
-
-	private static int windowSizeShift;
-
-	static boolean mmap;
-
-	static final ReferenceQueue<?> clearedWindowQueue;
-
-	private static ByteWindow[] cache;
-
-	private static ByteWindow lruHead;
-
-	private static ByteWindow lruTail;
-
-	private static int openFileCount;
-
-	private static int openByteCount;
+	private static volatile WindowCache cache;
 
 	static {
-		final WindowCacheConfig c = new WindowCacheConfig();
-		maxFileCount = c.getPackedGitOpenFiles();
-		maxByteCount = c.getPackedGitLimit();
-		windowSizeShift = bits(c.getPackedGitWindowSize());
-		windowSize = 1 << windowSizeShift;
-		mmap = c.isPackedGitMMAP();
-		cache = new ByteWindow[cacheTableSize()];
-		clearedWindowQueue = new ReferenceQueue<Object>();
-	}
-
-	private static int cacheTableSize() {
-		return 5 * (maxByteCount / windowSize) / 2;
+		reconfigure(new WindowCacheConfig());
 	}
 
 	/**
@@ -128,322 +102,144 @@ public static void reconfigure(final int packedGitLimit,
 	 *
 	 * @param cfg
 	 *            the new window cache configuration.
+	 * @throws IllegalArgumentException
+	 *             the cache configuration contains one or more invalid
+	 *             settings, usually too low of a limit.
 	 */
 	public static void reconfigure(final WindowCacheConfig cfg) {
-		reconfigureImpl(cfg);
+		final WindowCache nc = new WindowCache(cfg);
+		final WindowCache oc = cache;
+		if (oc != null)
+			oc.removeAll();
+		cache = nc;
 		UnpackedObjectCache.reconfigure(cfg);
 	}
 
-	private static synchronized void reconfigureImpl(final WindowCacheConfig cfg) {
-		boolean prune = false;
-		boolean evictAll = false;
-
-		if (maxFileCount < cfg.getPackedGitOpenFiles())
-			maxFileCount = cfg.getPackedGitOpenFiles();
-		else if (maxFileCount > cfg.getPackedGitOpenFiles()) {
-			maxFileCount = cfg.getPackedGitOpenFiles();
-			prune = true;
-		}
-
-		if (maxByteCount < cfg.getPackedGitLimit()) {
-			maxByteCount = cfg.getPackedGitLimit();
-		} else if (maxByteCount > cfg.getPackedGitLimit()) {
-			maxByteCount = cfg.getPackedGitLimit();
-			prune = true;
-		}
-
-		if (bits(cfg.getPackedGitWindowSize()) != windowSizeShift) {
-			windowSizeShift = bits(cfg.getPackedGitWindowSize());
-			windowSize = 1 << windowSizeShift;
-			evictAll = true;
-		}
-
-		if (mmap != cfg.isPackedGitMMAP()) {
-			mmap = cfg.isPackedGitMMAP();
-			evictAll = true;
-		}
-
-		if (evictAll) {
-			// We have to throw away every window we have. None
-			// of them are suitable for the new configuration.
+	static final ByteWindow get(final PackFile pack, final long offset)
+			throws IOException {
+		final WindowCache c = cache;
+		final ByteWindow r = c.getOrLoad(pack, c.toStart(offset));
+		if (c != cache) {
+			// The cache was reconfigured while we were using the old one
+			// to load this window. The window is still valid, but our
+			// cache may think its still live. Ensure the window is removed
+			// from the old cache so resources can be released.
 			//
-			for (ByteWindow<?> e : cache) {
-				for (; e != null; e = e.chainNext)
-					clear(e);
-			}
-			runClearedWindowQueue();
-			cache = new ByteWindow[cacheTableSize()];
-
-		} else {
-			if (prune) {
-				// We should decrease our memory usage.
-				//
-				releaseMemory();
-				runClearedWindowQueue();
-			}
-
-			if (cache.length != cacheTableSize()) {
-				// The cache table should be resized.
-				// Rehash every entry.
-				//
-				final ByteWindow[] priorTable = cache;
-
-				cache = new ByteWindow[cacheTableSize()];
-				for (ByteWindow<?> e : priorTable) {
-					for (ByteWindow<?> n; e != null; e = n) {
-						n = e.chainNext;
-						final int idx = hash(e.provider, e.id);
-						e.chainNext = cache[idx];
-						cache[idx] = e;
-					}
-				}
-			}
-		}
-	}
-
-	/**
-	 * Get a specific window.
-	 * 
-	 * @param curs
-	 *            an active cursor object to maintain the window reference while
-	 *            the caller needs it.
-	 * @param wp
-	 *            the provider of the window. If the window is not currently in
-	 *            the cache then the provider will be asked to load it.
-	 * @param position
-	 *            offset (in bytes) within the file that the caller needs access
-	 *            to.
-	 * @throws IOException
-	 *             the window was not found in the cache and the given provider
-	 *             was unable to load the window on demand.
-	 */
-	public static final void get(final WindowCursor curs, final PackFile wp,
-			final long position) throws IOException {
-		getImpl(curs, wp, position);
-		curs.window.ensureLoaded(curs.handle);
-	}
-
-	static synchronized final void pin(final PackFile wp) throws IOException {
-		if (++wp.openCount == 1) {
-			openFile(wp);
+			c.removeAll();
 		}
+		return r;
 	}
 
-	static synchronized final void unpin(final PackFile wp) {
-		if (--wp.openCount == 0) {
-			openFileCount--;
-			wp.cacheClose();
-		}
+	static final void purge(final PackFile pack) {
+		cache.removeAll(pack);
 	}
 
-	private static synchronized final void getImpl(final WindowCursor curs,
-			final PackFile wp, final long position) throws IOException {
-		final int id = (int) (position >> windowSizeShift);
-		final int idx = hash(wp, id);
-		for (ByteWindow<?> e = cache[idx]; e != null; e = e.chainNext) {
-			if (e.provider == wp && e.id == id) {
-				if ((curs.handle = e.get()) != null) {
-					curs.window = e;
-					makeMostRecent(e);
-					return;
-				}
+	private final int maxFiles;
 
-				clear(e);
-				break;
-			}
-		}
+	private final int maxBytes;
 
-		if (wp.openCount == 0) {
-			openFile(wp);
+	private final boolean mmap;
 
-			// The cacheOpen may have mapped the window we are trying to
-			// map ourselves. Retrying the search ensures that does not
-			// happen to us.
-			//
-			for (ByteWindow<?> e = cache[idx]; e != null; e = e.chainNext) {
-				if (e.provider == wp && e.id == id) {
-					if ((curs.handle = e.get()) != null) {
-						curs.window = e;
-						makeMostRecent(e);
-						return;
-					}
+	private final int windowSizeShift;
 
-					clear(e);
-					break;
-				}
-			}
-		}
+	private final int windowSize;
 
-		final int wsz = windowSize(wp, id);
-		wp.openCount++;
-		openByteCount += wsz;
-		releaseMemory();
-		runClearedWindowQueue();
+	private final AtomicInteger openFiles;
 
-		wp.allocWindow(curs, id, (position >>> windowSizeShift) << windowSizeShift, wsz);
-		final ByteWindow<?> e = curs.window;
-		e.chainNext = cache[idx];
-		cache[idx] = e;
-		insertLRU(e);
-	}
+	private final AtomicInteger openBytes;
 
-	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--;
-		}
-	}
+	private WindowCache(final WindowCacheConfig cfg) {
+		super(tableSize(cfg), lockCount(cfg));
+		maxFiles = cfg.getPackedGitOpenFiles();
+		maxBytes = cfg.getPackedGitLimit();
+		mmap = cfg.isPackedGitMMAP();
+		windowSizeShift = bits(cfg.getPackedGitWindowSize());
+		windowSize = 1 << windowSizeShift;
 
-	static synchronized void markLoaded(final ByteWindow w) {
-		if (--w.provider.openCount == 0) {
-			openFileCount--;
-			w.provider.cacheClose();
-		}
-	}
+		openFiles = new AtomicInteger();
+		openBytes = new AtomicInteger();
 
-	private static void makeMostRecent(ByteWindow<?> e) {
-		if (lruHead != e) {
-			unlinkLRU(e);
-			insertLRU(e);
-		}
+		if (maxFiles < 1)
+			throw new IllegalArgumentException("Open files must be >= 1");
+		if (maxBytes < windowSize)
+			throw new IllegalArgumentException("Window size must be < limit");
 	}
 
-	private static void releaseMemory() {
-		ByteWindow<?> e = lruTail;
-		while (isOverLimit() && e != null) {
-			final ByteWindow<?> p = e.lruPrev;
-			clear(e);
-			e = p;
-		}
+	@Override
+	protected int hash(final int packHash, final long off) {
+		return packHash + (int) (off >>> windowSizeShift);
 	}
 
-	private static boolean isOverLimit() {
-		return openByteCount > maxByteCount || openFileCount > maxFileCount;
-	}
-
-	/**
-	 * Remove all windows associated with a specific provider.
-	 * <p>
-	 * Providers should invoke this method as part of their cleanup/close
-	 * routines, ensuring that the window cache releases all windows that cannot
-	 * ever be requested again.
-	 * </p>
-	 * 
-	 * @param wp
-	 *            the window provider whose windows should be removed from the
-	 *            cache.
-	 */
-	public static synchronized final void purge(final PackFile wp) {
-		for (ByteWindow e : cache) {
-			for (; e != null; e = e.chainNext) {
-				if (e.provider == wp)
-					clear(e);
-			}
+	@Override
+	protected ByteWindow load(final PackFile pack, final long offset)
+			throws IOException {
+		if (pack.beginWindowCache())
+			openFiles.incrementAndGet();
+		try {
+			if (mmap)
+				return pack.mmap(offset, windowSize);
+			return pack.read(offset, windowSize);
+		} catch (IOException e) {
+			close(pack);
+			throw e;
+		} catch (RuntimeException e) {
+			close(pack);
+			throw e;
+		} catch (Error e) {
+			close(pack);
+			throw e;
 		}
-		runClearedWindowQueue();
 	}
 
-	private static void runClearedWindowQueue() {
-		ByteWindow<?> e;
-		while ((e = (ByteWindow) clearedWindowQueue.poll()) != null) {
-			unlinkSize(e);
-			unlinkLRU(e);
-			unlinkCache(e);
-			e.chainNext = null;
-			e.lruNext = null;
-			e.lruPrev = null;
-		}
+	@Override
+	protected WindowRef createRef(final PackFile p, final long o,
+			final ByteWindow v) {
+		final WindowRef ref = new WindowRef(p, o, v, queue);
+		openBytes.addAndGet(ref.size);
+		return ref;
 	}
 
-	private static void clear(final ByteWindow<?> e) {
-		unlinkSize(e);
-		e.clear();
-		e.enqueue();
+	@Override
+	protected void clear(final WindowRef ref) {
+		openBytes.addAndGet(-ref.size);
+		close(ref.pack);
 	}
 
-	private static void unlinkSize(final ByteWindow<?> e) {
-		if (e.sizeActive) {
-			if (--e.provider.openCount == 0) {
-				openFileCount--;
-				e.provider.cacheClose();
-			}
-			openByteCount -= e.size;
-			e.sizeActive = false;
-		}
+	private void close(final PackFile pack) {
+		if (pack.endWindowCache())
+			openFiles.decrementAndGet();
 	}
 
-	private static void unlinkCache(final ByteWindow dead) {
-		final int idx = hash(dead.provider, dead.id);
-		ByteWindow<?> e = cache[idx], p = null, n;
-		for (; e != null; p = e, e = n) {
-			n = e.chainNext;
-			if (e == dead) {
-				if (p == null)
-					cache[idx] = n;
-				else
-					p.chainNext = n;
-				break;
-			}
-		}
+	@Override
+	protected boolean isFull() {
+		return maxFiles < openFiles.get() || maxBytes < openBytes.get();
 	}
 
-	private static void unlinkLRU(final ByteWindow e) {
-		final ByteWindow<?> prev = e.lruPrev;
-		final ByteWindow<?> next = e.lruNext;
-
-		if (prev != null)
-			prev.lruNext = next;
-		else
-			lruHead = next;
-
-		if (next != null)
-			next.lruPrev = prev;
-		else
-			lruTail = prev;
+	private long toStart(final long offset) {
+		return (offset >>> windowSizeShift) << windowSizeShift;
 	}
 
-	private static void insertLRU(final ByteWindow<?> e) {
-		final ByteWindow h = lruHead;
-		e.lruPrev = null;
-		e.lruNext = h;
-		if (h != null)
-			h.lruPrev = e;
-		else
-			lruTail = e;
-		lruHead = e;
+	private static int tableSize(final WindowCacheConfig cfg) {
+		final int wsz = cfg.getPackedGitWindowSize();
+		final int limit = cfg.getPackedGitLimit();
+		if (wsz <= 0)
+			throw new IllegalArgumentException("Invalid window size");
+		if (limit < wsz)
+			throw new IllegalArgumentException("Window size must be < limit");
+		return 5 * (limit / wsz) / 2;
 	}
 
-	private static int hash(final PackFile wp, final int id) {
-		// wp.hash was already "stirred up" a bit by * 31 when
-		// it was created. Its reasonable to just add here.
-		//
-		return ((wp.hash + id) >>> 1) % cache.length;
+	private static int lockCount(final WindowCacheConfig cfg) {
+		return Math.max(cfg.getPackedGitOpenFiles(), 32);
 	}
 
-	private static int windowSize(final PackFile file, final int id) {
-		final long len = file.length;
-		final long pos = id << windowSizeShift;
-		return len < pos + windowSize ? (int) (len - pos) : windowSize;
-	}
+	static class WindowRef extends OffsetCache.Ref<ByteWindow> {
+		final int size;
 
-	private WindowCache() {
-		throw new UnsupportedOperationException();
+		WindowRef(final PackFile pack, final long position, final ByteWindow v,
+				final ReferenceQueue<ByteWindow> queue) {
+			super(pack, position, v, queue);
+			size = v.size();
+		}
 	}
 }
diff --git a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCursor.java b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCursor.java
index fb9d348..0723a78 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCursor.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCursor.java
@@ -48,14 +48,12 @@
 
 	private Inflater inf;
 
-	ByteWindow window;
-
-	Object handle;
+	private ByteWindow window;
 
 	/**
 	 * Copy bytes from the window to a caller supplied buffer.
 	 * 
-	 * @param provider
+	 * @param pack
 	 *            the file the desired window is stored within.
 	 * @param position
 	 *            position within the file to read from.
@@ -74,13 +72,13 @@
 	 *             this cursor does not match the provider or id and the proper
 	 *             window could not be acquired through the provider's cache.
 	 */
-	int copy(final PackFile provider, long position, final byte[] dstbuf,
+	int copy(final PackFile pack, long position, final byte[] dstbuf,
 			int dstoff, final int cnt) throws IOException {
-		final long length = provider.length;
+		final long length = pack.length;
 		int need = cnt;
 		while (need > 0 && position < length) {
-			pin(provider, position);
-			final int r = window.copy(handle, position, dstbuf, dstoff, need);
+			pin(pack, position);
+			final int r = window.copy(position, dstbuf, dstoff, need);
 			position += r;
 			dstoff += r;
 			need -= r;
@@ -91,7 +89,7 @@ int copy(final PackFile provider, long position, final byte[] dstbuf,
 	/**
 	 * Pump bytes into the supplied inflater as input.
 	 * 
-	 * @param provider
+	 * @param pack
 	 *            the file the desired window is stored within.
 	 * @param position
 	 *            position within the file to read from.
@@ -109,47 +107,53 @@ int copy(final PackFile provider, long position, final byte[] dstbuf,
 	 *             the inflater encountered an invalid chunk of data. Data
 	 *             stream corruption is likely.
 	 */
-	int inflate(final PackFile provider, long position, final byte[] dstbuf,
+	int inflate(final PackFile pack, long position, final byte[] dstbuf,
 			int dstoff) throws IOException, DataFormatException {
 		if (inf == null)
 			inf = InflaterCache.get();
 		else
 			inf.reset();
 		for (;;) {
-			pin(provider, position);
-			dstoff = window.inflate(handle, position, dstbuf, dstoff, inf);
+			pin(pack, position);
+			dstoff = window.inflate(position, dstbuf, dstoff, inf);
 			if (inf.finished())
 				return dstoff;
 			position = window.end;
 		}
 	}
 
-	void inflateVerify(final PackFile provider, long position)
+	void inflateVerify(final PackFile pack, long position)
 			throws IOException, DataFormatException {
 		if (inf == null)
 			inf = InflaterCache.get();
 		else
 			inf.reset();
 		for (;;) {
-			pin(provider, position);
-			window.inflateVerify(handle, position, inf);
+			pin(pack, position);
+			window.inflateVerify(position, inf);
 			if (inf.finished())
 				return;
 			position = window.end;
 		}
 	}
 
-	private void pin(final PackFile provider, final long position)
+	private void pin(final PackFile pack, final long position)
 			throws IOException {
 		final ByteWindow w = window;
-		if (w == null || !w.contains(provider, position))
-			WindowCache.get(this, provider, position);
+		if (w == null || !w.contains(pack, position)) {
+			// If memory is low, we may need what is in our window field to
+			// be cleaned up by the GC during the get for the next window.
+			// So we always clear it, even though we are just going to set
+			// it again.
+			//
+			window = null;
+			window = WindowCache.get(pack, position);
+		}
 	}
 
 	/** Release the current window cursor. */
 	public void release() {
 		window = null;
-		handle = null;
 		try {
 			InflaterCache.release(inf);
 		} finally {
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 10/11] Add tests for WindowCache.reconfigure cases

[Shawn O. Pearce]

Most of these cases occur when the window cache is misconfigured
by the application.  We should be throwing an exception out with
some sort of error message if they happen, so check for that.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 New test, to get better coverage.

 .../jgit/lib/WindowCacheReconfigureTest.java       |  119 ++++++++++++++++++++
 1 files changed, 119 insertions(+), 0 deletions(-)
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheReconfigureTest.java

diff --git a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheReconfigureTest.java b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheReconfigureTest.java
new file mode 100644
index 0000000..9bd4d96
--- /dev/null
+++ b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheReconfigureTest.java
@@ -0,0 +1,119 @@
+/*
+ * Copyright (C) 2009, Google Inc.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Git Development Community nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.spearce.jgit.lib;
+
+public class WindowCacheReconfigureTest extends RepositoryTestCase {
+	public void testConfigureCache_PackedGitLimit_0() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitLimit(0);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitLimit = 0");
+		} catch (IllegalArgumentException e) {
+			//
+		}
+	}
+
+	public void testConfigureCache_PackedGitWindowSize_0() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitWindowSize(0);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitWindowSize = 0");
+		} catch (IllegalArgumentException e) {
+			assertEquals("Invalid window size", e.getMessage());
+		}
+	}
+
+	public void testConfigureCache_PackedGitWindowSize_512() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitWindowSize(512);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitWindowSize = 512");
+		} catch (IllegalArgumentException e) {
+			assertEquals("Invalid window size", e.getMessage());
+		}
+	}
+
+	public void testConfigureCache_PackedGitWindowSize_4097() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitWindowSize(4097);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitWindowSize = 4097");
+		} catch (IllegalArgumentException e) {
+			assertEquals("Window size must be power of 2", e.getMessage());
+		}
+	}
+
+	public void testConfigureCache_PackedGitOpenFiles_0() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitOpenFiles(0);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitOpenFiles = 0");
+		} catch (IllegalArgumentException e) {
+			assertEquals("Open files must be >= 1", e.getMessage());
+		}
+	}
+
+	public void testConfigureCache_PackedGitWindowSizeAbovePackedGitLimit() {
+		try {
+			final WindowCacheConfig cfg = new WindowCacheConfig();
+			cfg.setPackedGitLimit(1024);
+			cfg.setPackedGitWindowSize(8192);
+			WindowCache.reconfigure(cfg);
+			fail("incorrectly permitted PackedGitWindowSize > PackedGitLimit");
+		} catch (IllegalArgumentException e) {
+			assertEquals("Window size must be < limit", e.getMessage());
+		}
+	}
+
+	public void testConfigureCache_Limits1() {
+		// This test is just to force coverage over some lower bounds for
+		// the table. We don't want the table to wind up with too small
+		// of a size. This is highly dependent upon the table allocation
+		// algorithm actually implemented in WindowCache.
+		//
+		final WindowCacheConfig cfg = new WindowCacheConfig();
+		cfg.setPackedGitLimit(6 * 4096 / 5);
+		cfg.setPackedGitWindowSize(4096);
+		WindowCache.reconfigure(cfg);
+	}
+}
-- 
1.6.3.rc3.199.g24398

[JGIT PATCH 11/11] Add tests to increase coverage of WindowCache

[Shawn O. Pearce]

These tests run the WindowCache in different configurations with known
inputs, forcing it through different code paths as the cache populates
with entries, and potentially overflows.

The list of objects was derived from `git verify-pack -v`, run over all
of the pack files we install by default into a RepositoryTestCase.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---

 New test, to get better coverage.

 .../jgit/test/resources/all_packed_objects.txt     |   96 +++++++++++++
 .../org/spearce/jgit/lib/WindowCacheGetTest.java   |  143 ++++++++++++++++++++
 .../org/spearce/jgit/lib/PackedObjectLoader.java   |    7 +
 .../src/org/spearce/jgit/lib/WindowCache.java      |   12 ++
 4 files changed, 258 insertions(+), 0 deletions(-)
 create mode 100644 org.spearce.jgit.test/tst-rsrc/org/spearce/jgit/test/resources/all_packed_objects.txt
 create mode 100644 org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheGetTest.java

diff --git a/org.spearce.jgit.test/tst-rsrc/org/spearce/jgit/test/resources/all_packed_objects.txt b/org.spearce.jgit.test/tst-rsrc/org/spearce/jgit/test/resources/all_packed_objects.txt
new file mode 100644
index 0000000..a97f662
--- /dev/null
+++ b/org.spearce.jgit.test/tst-rsrc/org/spearce/jgit/test/resources/all_packed_objects.txt
@@ -0,0 +1,96 @@
+4b825dc642cb6eb9a060e54bf8d69288fbee4904 tree   0 9 7782
+540a36d136cf413e4b064c2b0e0a4db60f77feab commit 191 131 339
+5b6e7c66c276e7610d4a73c70ec1a1f7c1003259 blob   11 40 516 1 6ff87c4664981e4397625791c8ea3bbb5f2279a3
+6ff87c4664981e4397625791c8ea3bbb5f2279a3 blob   18787 7180 556
+82c6b885ff600be425b4ea96dee75dca255b69e7 commit 245 166 12
+902d5476fa249b7abc9d84c611577a81381f0327 tree   35 46 7736
+aabf2ffaec9b497f0950352b3e582d73035c2035 tree   35 46 470
+c59759f143fb1fe21c197981df75a7ee00290799 commit 240 161 178
+02ba32d3649e510002c21651936b7077aa75ffa9 tree   122 127 3806
+0966a434eb1a025db6b71485ab63a3bfbea520b6 commit 287 197 2611
+09efc7e59a839528ac7bda9fa020dc9101278680 tree   68 71 5497
+0a3d7772488b6b106fb62813c4d6d627918d9181 tree   98 95 3367
+1004d0d7ac26fbf63050a234c9b88a46075719d3 tree   68 72 3504
+10da5895682013006950e7da534b705252b03be6 blob   6 15 3591
+1203b03dc816ccbb67773f28b3c19318654b0bc8 commit 222 152 758
+15fae9e651043de0fd1deef588aa3fbf5a7a41c6 blob   6 15 3474
+16f9ec009e5568c435f473ba3a1df732d49ce8c3 blob   3 12 4196
+1fd7d579fb6ae3fe942dc09c2c783443d04cf21e blob   6 15 3678
+20a8ade77639491ea0bd667bf95de8abf3a434c8 tree   66 77 5663
+2675188fd86978d5bc4d7211698b2118ae3bf658 tree   68 72 4124
+2c349335b7f797072cf729c4f3bb0914ecb6dec9 commit 221 154 2457
+2cc3f4155a8eda5c3f1bc85de0988c0155c8cc1c tree   68 72 4717
+30a7b072d441dbfcfe0266b1c5fce94c22c447da tree   38 48 5784
+42e4e7c5e507e113ebbb7801b16b52cf867b7ce1 commit 184 133 1407
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diff --git a/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheGetTest.java b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheGetTest.java
new file mode 100644
index 0000000..c19bb2b
--- /dev/null
+++ b/org.spearce.jgit.test/tst/org/spearce/jgit/lib/WindowCacheGetTest.java
@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2009, Google Inc.
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Git Development Community nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.spearce.jgit.lib;
+
+import java.io.BufferedReader;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.spearce.jgit.errors.CorruptObjectException;
+import org.spearce.jgit.util.JGitTestUtil;
+import org.spearce.jgit.util.MutableInteger;
+
+public class WindowCacheGetTest extends RepositoryTestCase {
+	private List<TestObject> toLoad;
+
+	@Override
+	public void setUp() throws Exception {
+		super.setUp();
+
+		toLoad = new ArrayList<TestObject>();
+		final BufferedReader br = new BufferedReader(new InputStreamReader(
+				new FileInputStream(JGitTestUtil
+						.getTestResourceFile("all_packed_objects.txt")),
+				Constants.CHARSET));
+		try {
+			String line;
+			while ((line = br.readLine()) != null) {
+				final String[] parts = line.split(" {1,}");
+				final TestObject o = new TestObject();
+				o.id = ObjectId.fromString(parts[0]);
+				o.setType(parts[1]);
+				o.rawSize = Integer.parseInt(parts[2]);
+				// parts[3] is the size-in-pack
+				o.offset = Long.parseLong(parts[4]);
+				toLoad.add(o);
+			}
+		} finally {
+			br.close();
+		}
+		assertEquals(96, toLoad.size());
+	}
+
+	public void testCache_Defaults() throws IOException {
+		final WindowCacheConfig cfg = new WindowCacheConfig();
+		WindowCache.reconfigure(cfg);
+		doCacheTests();
+		checkLimits(cfg);
+
+		final WindowCache cache = WindowCache.getInstance();
+		assertEquals(6, cache.getOpenFiles());
+		assertEquals(17346, cache.getOpenBytes());
+	}
+
+	public void testCache_TooFewFiles() throws IOException {
+		final WindowCacheConfig cfg = new WindowCacheConfig();
+		cfg.setPackedGitOpenFiles(2);
+		WindowCache.reconfigure(cfg);
+		doCacheTests();
+		checkLimits(cfg);
+	}
+
+	public void testCache_TooSmallLimit() throws IOException {
+		final WindowCacheConfig cfg = new WindowCacheConfig();
+		cfg.setPackedGitWindowSize(4096);
+		cfg.setPackedGitLimit(4096);
+		WindowCache.reconfigure(cfg);
+		doCacheTests();
+		checkLimits(cfg);
+	}
+
+	private void checkLimits(final WindowCacheConfig cfg) {
+		final WindowCache cache = WindowCache.getInstance();
+		assertTrue(cache.getOpenFiles() <= cfg.getPackedGitOpenFiles());
+		assertTrue(cache.getOpenBytes() <= cfg.getPackedGitLimit());
+		assertTrue(0 < cache.getOpenFiles());
+		assertTrue(0 < cache.getOpenBytes());
+	}
+
+	private void doCacheTests() throws IOException {
+		for (final TestObject o : toLoad) {
+			final ObjectLoader or = db.openObject(o.id);
+			assertNotNull(or);
+			assertTrue(or instanceof PackedObjectLoader);
+			assertEquals(o.type, or.getType());
+			assertEquals(o.rawSize, or.getRawSize());
+			assertEquals(o.offset, ((PackedObjectLoader) or).getObjectOffset());
+		}
+	}
+
+	private class TestObject {
+		ObjectId id;
+
+		int type;
+
+		int rawSize;
+
+		long offset;
+
+		void setType(final String typeStr) throws CorruptObjectException {
+			final byte[] typeRaw = Constants.encode(typeStr + " ");
+			final MutableInteger ptr = new MutableInteger();
+			type = Constants.decodeTypeString(id, typeRaw, (byte) ' ', ptr);
+		}
+	}
+}
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 0c3e783..29ec6d3 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/PackedObjectLoader.java
@@ -99,6 +99,13 @@ public final long getSize() {
 	}
 
 	/**
+	 * @return offset of object header within pack file
+	 */
+	public final long getObjectOffset() {
+		return objectOffset;
+	}
+
+	/**
 	 * @return offset of object data within pack file
 	 */
 	public final long getDataOffset() {
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 0102a2d..0c60853 100644
--- a/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
+++ b/org.spearce.jgit/src/org/spearce/jgit/lib/WindowCache.java
@@ -115,6 +115,10 @@ public static void reconfigure(final WindowCacheConfig cfg) {
 		UnpackedObjectCache.reconfigure(cfg);
 	}
 
+	static WindowCache getInstance() {
+		return cache;
+	}
+
 	static final ByteWindow get(final PackFile pack, final long offset)
 			throws IOException {
 		final WindowCache c = cache;
@@ -165,6 +169,14 @@ private WindowCache(final WindowCacheConfig cfg) {
 			throw new IllegalArgumentException("Window size must be < limit");
 	}
 
+	int getOpenFiles() {
+		return openFiles.get();
+	}
+
+	int getOpenBytes() {
+		return openBytes.get();
+	}
+
 	@Override
 	protected int hash(final int packHash, final long off) {
 		return packHash + (int) (off >>> windowSizeShift);
-- 
1.6.3.rc3.199.g24398

Re: [JGIT PATCH v2 00/11] WindowCache rewrite... with tests

[Robin Rosenberg]

onsdag 29 april 2009 20:54:37 skrev "Shawn O. Pearce" <spearce@spearce.org>:
> 9-11 is the rewrite of WindowCache, with new unit tests to get higher
> levels of coverage in this section of the code.  Actually doing
> better is really hard, as we'd need to cause thread race conditions
> deep within critical sections.  The only way I can think to do that
> is to add injection points where we can insert "evil other thread"
> logic during the unit test, and rely on the JIT to compile them
> out in normal application usage.  Ick.  Its also quite fragile.

Testing *is* hard. No news here. There are various techniques for 
injecting code using AOP (AspjectJ) that may be useful for testing,
since we could inject failures that way without the overhead of
injection points in normal execution. 

-- robin