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Lazy load note subtrees from fanout levels 

Instead of reading a note tree recursively up front when the NoteMap
is loaded, read only the root tree and load subtrees on demand when
they are accessed by the application.  This gives a lower latency
to read a note for the recent commits on a branch, as only the paths
that are needed get read.

Given a 2/38 style fanout, the tree will fully load when 256 objects
have been accessed by the application.  But unlike the prior version
of NoteMap, the NoteMap will load faster and answer lookups sooner,
as the loading time for all 256 levels is spread out across each of
the get() requests.

Given a 2/2/36 style fanout, the tree won't need to fully load until
about 65,536 objects are accessed.

To simplify the implementation we only support the flat layout (all
notes in the top level tree), or a 2/38, 2/2/36, 2/2/2/34, through
2/.../2 style fanout.  Unlike C Git we don't support reading the old
experimental 4/36 fanout.  This is sufficient because C Git won't
create the 4/36 style fanout when creating or updating a notes tree,
and there really aren't any in the wild today.

Change-Id: I6099b35916a8404762f31e9c11f632e43e0c1bfd
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
tags/v0.10.1
Shawn O. Pearce 13 years ago
parent
936820988f
commit
b81b97fbdd
6 changed files with 557 additions and 69 deletions
Split View Show Diff Stats
  1. 126
    0
      org.eclipse.jgit/src/org/eclipse/jgit/notes/FanoutBucket.java
  2. 60
    0
      org.eclipse.jgit/src/org/eclipse/jgit/notes/InMemoryNoteBucket.java
  3. 111
    0
      org.eclipse.jgit/src/org/eclipse/jgit/notes/LeafBucket.java
  4. 61
    0
      org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteBucket.java
  5. 15
    69
      org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteMap.java
  6. 184
    0
      org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteParser.java

+ 126
- 0
org.eclipse.jgit/src/org/eclipse/jgit/notes/FanoutBucket.java View File

@@ -0,0 +1,126 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* 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 Eclipse Foundation, Inc. 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.eclipse.jgit.notes;

import java.io.IOException;

import org.eclipse.jgit.lib.AbbreviatedObjectId;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;

/**
* A note tree holding only note subtrees, each named using a 2 digit hex name.
*
* The fanout buckets/trees contain on average 256 subtrees, naming the subtrees
* by a slice of the ObjectId contained within them, from "00" through "ff".
*
* Each fanout bucket has a {@link #prefixLen} that defines how many digits it
* skips in an ObjectId before it gets to the digits matching {@link #table}.
*
* The root tree has {@code prefixLen == 0}, and thus does not skip any digits.
* For ObjectId "c0ffee...", the note (if it exists) will be stored within the
* bucket {@code table[0xc0]}.
*
* The first level tree has {@code prefixLen == 2}, and thus skips the first two
* digits. For the same example "c0ffee..." object, its note would be found
* within the {@code table[0xff]} bucket (as first 2 digits "c0" are skipped).
*
* Each subtree is loaded on-demand, reducing startup latency for reads that
* only need to examine a few objects. However, due to the rather uniform
* distribution of the SHA-1 hash that is used for ObjectIds, accessing 256
* objects is very likely to load all of the subtrees into memory.
*
* A FanoutBucket must be parsed from a tree object by {@link NoteParser}.
*/
class FanoutBucket extends InMemoryNoteBucket {
/**
* Fan-out table similar to the PackIndex structure.
*
* Notes for an object are stored within the sub-bucket that is held here as
* {@code table[ objectId.getByte( prefixLen / 2 ) ]}. If the slot is null
* there are no notes with that prefix.
*/
private final NoteBucket[] table;

FanoutBucket(int prefixLen) {
super(prefixLen);
table = new NoteBucket[256];
}

void parseOneEntry(int cell, ObjectId id) {
table[cell] = new LazyNoteBucket(id);
}

@Override
ObjectId get(AnyObjectId objId, ObjectReader or) throws IOException {
NoteBucket b = table[cell(objId)];
return b != null ? b.get(objId, or) : null;
}

private int cell(AnyObjectId id) {
return id.getByte(prefixLen >> 1);
}

private class LazyNoteBucket extends NoteBucket {
private final ObjectId treeId;

LazyNoteBucket(ObjectId treeId) {
this.treeId = treeId;
}

@Override
ObjectId get(AnyObjectId objId, ObjectReader or) throws IOException {
return load(objId, or).get(objId, or);
}

private NoteBucket load(AnyObjectId objId, ObjectReader or)
throws IOException {
AbbreviatedObjectId p = objId.abbreviate(prefixLen + 2);
NoteBucket self = NoteParser.parse(p, treeId, or);
table[cell(objId)] = self;
return self;
}
}
}

+ 60
- 0
org.eclipse.jgit/src/org/eclipse/jgit/notes/InMemoryNoteBucket.java View File

@@ -0,0 +1,60 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* 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 Eclipse Foundation, Inc. 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.eclipse.jgit.notes;

/** A note bucket that has been loaded into the process. */
abstract class InMemoryNoteBucket extends NoteBucket {
/**
* Number of leading digits that leads to this bucket in the note path.
*
* This is counted in terms of hex digits, not raw bytes. Each bucket level
* is typically 2 higher than its parent, placing about 256 items in each
* level of the tree.
*/
final int prefixLen;

InMemoryNoteBucket(int prefixLen) {
this.prefixLen = prefixLen;
}
}

+ 111
- 0
org.eclipse.jgit/src/org/eclipse/jgit/notes/LeafBucket.java View File

@@ -0,0 +1,111 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* 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 Eclipse Foundation, Inc. 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.eclipse.jgit.notes;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;

/**
* A note tree holding only notes, with no subtrees.
*
* The leaf bucket contains on average less than 256 notes, all of whom share
* the same leading prefix. If a notes branch has less than 256 notes, the top
* level tree of the branch should be a LeafBucket. Once a notes branch has more
* than 256 notes, the root should be a {@link FanoutBucket} and the LeafBucket
* will appear only as a cell of a FanoutBucket.
*
* Entries within the LeafBucket are stored sorted by ObjectId, and lookup is
* performed using binary search. As the entry list should contain fewer than
* 256 elements, the average number of compares to find an element should be
* less than 8 due to the O(log N) lookup behavior.
*
* A LeafBucket must be parsed from a tree object by {@link NoteParser}.
*/
class LeafBucket extends InMemoryNoteBucket {
/** All note blobs in this bucket, sorted sequentially. */
private Note[] notes;

/** Number of items in {@link #notes}. */
private int cnt;

LeafBucket(int prefixLen) {
super(prefixLen);
notes = new Note[4];
}

private int search(AnyObjectId objId) {
int low = 0;
int high = cnt;
while (low < high) {
int mid = (low + high) >>> 1;
int cmp = objId.compareTo(notes[mid]);
if (cmp < 0)
high = mid;
else if (cmp == 0)
return mid;
else
low = mid + 1;
}
return -(low + 1);
}

ObjectId get(AnyObjectId objId, ObjectReader or) {
int idx = search(objId);
return 0 <= idx ? notes[idx].getData() : null;
}

void parseOneEntry(AnyObjectId noteOn, AnyObjectId noteData) {
growIfFull();
notes[cnt++] = new Note(noteOn, noteData.copy());
}

private void growIfFull() {
if (notes.length == cnt) {
Note[] n = new Note[notes.length * 2];
System.arraycopy(notes, 0, n, 0, cnt);
notes = n;
}
}
}

+ 61
- 0
org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteBucket.java View File

@@ -0,0 +1,61 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* 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 Eclipse Foundation, Inc. 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.eclipse.jgit.notes;

import java.io.IOException;

import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;

/**
* A tree that stores note objects.
*
* @see FanoutBucket
* @see LeafBucket
*/
abstract class NoteBucket {
abstract ObjectId get(AnyObjectId objId, ObjectReader reader)
throws IOException;
}

+ 15
- 69
org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteMap.java View File

@@ -49,26 +49,20 @@ import org.eclipse.jgit.errors.CorruptObjectException;
import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.errors.LargeObjectException;
import org.eclipse.jgit.errors.MissingObjectException;
import org.eclipse.jgit.lib.AbbreviatedObjectId;
import org.eclipse.jgit.lib.AnyObjectId;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectIdSubclassMap;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevTree;
import org.eclipse.jgit.treewalk.TreeWalk;
import org.eclipse.jgit.util.RawParseUtils;

/**
* Index of notes from a note branch.
*
* This class is not thread-safe, and relies on an {@link ObjectReader} that it
* borrows/shares with the caller.
*
* The current implementation is not very efficient. During load it recursively
* scans the entire note branch and indexes all annotated objects. If there are
* more than 256 notes in the branch, and not all of them will be accessed by
* the caller, this aggressive up-front loading probably takes too much time.
* borrows/shares with the caller. The reader can be used during any call, and
* is not released by this class. The caller should arrange for releasing the
* shared {@code ObjectReader} at the proper times.
*/
public class NoteMap {
/**
@@ -152,7 +146,7 @@ public class NoteMap {
private final ObjectReader reader;

/** All of the notes that have been loaded. */
private ObjectIdSubclassMap<Note> notes = new ObjectIdSubclassMap<Note>();
private InMemoryNoteBucket root;

private NoteMap(ObjectReader reader) {
this.reader = reader;
@@ -164,10 +158,11 @@ public class NoteMap {
* @param id
* the object to look for.
* @return the note's blob ObjectId, or null if no note exists.
* @throws IOException
* a portion of the note space is not accessible.
*/
public ObjectId get(AnyObjectId id) {
Note note = notes.get(id);
return note != null ? note.getData() : null;
public ObjectId get(AnyObjectId id) throws IOException {
return root.get(id, reader);
}

/**
@@ -176,8 +171,10 @@ public class NoteMap {
* @param id
* the object to look for.
* @return true if a note exists; false if there is no note.
* @throws IOException
* a portion of the note space is not accessible.
*/
public boolean contains(AnyObjectId id) {
public boolean contains(AnyObjectId id) throws IOException {
return get(id) != null;
}

@@ -216,60 +213,9 @@ public class NoteMap {
return null;
}

private void load(ObjectId treeId) throws MissingObjectException,
private void load(ObjectId rootTree) throws MissingObjectException,
IncorrectObjectTypeException, CorruptObjectException, IOException {
try {
byte[] idBuf = new byte[Constants.OBJECT_ID_LENGTH];
TreeWalk tw = new TreeWalk(reader);
tw.reset();
tw.setRecursive(true);
tw.addTree(treeId);

notes.clear();

while (tw.next()) {
ObjectId pathId = pathToId(idBuf, tw.getRawPath());
if (pathId != null)
notes.add(new Note(pathId, tw.getObjectId(0)));
}
} finally {
reader.release();
}
}

private static ObjectId pathToId(byte[] rawIdBuf, byte[] path) {
int r = 0;

for (int i = 0; i < path.length; i++) {
byte c = path[i];

// Skip embedded '/' in paths, these aren't part of a name.
if (c == '/')
continue;

// We need at least 2 digits to consume in this cycle.
if (path.length < i + 2)
return null;

// We cannot exceed an ObjectId raw length.
if (r == Constants.OBJECT_ID_STRING_LENGTH)
return null;

int high, low;
try {
high = RawParseUtils.parseHexInt4(c);
low = RawParseUtils.parseHexInt4(path[++i]);
} catch (ArrayIndexOutOfBoundsException notHex) {
return null;
}

rawIdBuf[r++] = (byte) ((high << 4) | low);
}

// We need exactly the right number of input bytes.
if (r == Constants.OBJECT_ID_LENGTH)
return ObjectId.fromRaw(rawIdBuf);
else
return null;
AbbreviatedObjectId none = AbbreviatedObjectId.fromString("");
root = NoteParser.parse(none, rootTree, reader);
}
}

+ 184
- 0
org.eclipse.jgit/src/org/eclipse/jgit/notes/NoteParser.java View File

@@ -0,0 +1,184 @@
/*
* Copyright (C) 2010, Google Inc.
* and other copyright owners as documented in the project's IP log.
*
* This program and the accompanying materials are made available
* under the terms of the Eclipse Distribution License v1.0 which
* accompanies this distribution, is reproduced below, and is
* available at http://www.eclipse.org/org/documents/edl-v10.php
*
* 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 Eclipse Foundation, Inc. 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.eclipse.jgit.notes;

import static org.eclipse.jgit.lib.Constants.OBJECT_ID_STRING_LENGTH;
import static org.eclipse.jgit.lib.Constants.encodeASCII;
import static org.eclipse.jgit.lib.FileMode.TREE;
import static org.eclipse.jgit.util.RawParseUtils.parseHexInt4;

import java.io.IOException;

import org.eclipse.jgit.errors.IncorrectObjectTypeException;
import org.eclipse.jgit.lib.AbbreviatedObjectId;
import org.eclipse.jgit.lib.MutableObjectId;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.treewalk.CanonicalTreeParser;

/** Custom tree parser to select note bucket type and load it. */
final class NoteParser extends CanonicalTreeParser {
/**
* Parse a tree object into a {@link NoteBucket} instance.
*
* The type of note tree is automatically detected by examining the items
* within the tree, and allocating the proper storage type based on the
* first note-like entry encountered. Since the method parses by guessing
* the type on the first element, malformed note trees can be read as the
* wrong type of tree.
*
* This method is not recursive, it parses the one tree given to it and
* returns the bucket. If there are subtrees for note storage, they are
* setup as lazy pointers that will be resolved at a later time.
*
* @param prefix
* common hex digits that all notes within this tree share. The
* root tree has {@code prefix.length() == 0}, the first-level
* subtrees should be {@code prefix.length()==2}, etc.
* @param treeId
* the tree to read from the repository.
* @param reader
* reader to access the tree object.
* @return bucket to holding the notes of the specified tree.
* @throws IOException
* {@code treeId} cannot be accessed.
*/
static InMemoryNoteBucket parse(AbbreviatedObjectId prefix,
final ObjectId treeId, final ObjectReader reader)
throws IOException {
return new NoteParser(prefix, reader, treeId).parseTree();
}

private final AbbreviatedObjectId prefix;

private final int pathPadding;

private NoteParser(AbbreviatedObjectId p, ObjectReader r, ObjectId t)
throws IncorrectObjectTypeException, IOException {
super(encodeASCII(p.name()), r, t);
prefix = p;

// Our path buffer has a '/' that we don't want after the prefix.
// Drop it by shifting the path down one position.
pathPadding = 0 < prefix.length() ? 1 : 0;
if (0 < pathPadding)
System.arraycopy(path, 0, path, pathPadding, prefix.length());
}

private InMemoryNoteBucket parseTree() {
for (; !eof(); next(1)) {
if (pathLen == pathPadding + OBJECT_ID_STRING_LENGTH && isHex())
return parseLeafTree();

else if (getNameLength() == 2 && isHex() && isTree())
return parseFanoutTree();
}

// If we cannot determine the style used, assume its a leaf.
return new LeafBucket(prefix.length());
}

private LeafBucket parseLeafTree() {
final LeafBucket leaf = new LeafBucket(prefix.length());
final MutableObjectId idBuf = new MutableObjectId();

for (; !eof(); next(1)) {
if (parseObjectId(idBuf))
leaf.parseOneEntry(idBuf, getEntryObjectId());
}

return leaf;
}

private boolean parseObjectId(MutableObjectId id) {
if (pathLen == pathPadding + OBJECT_ID_STRING_LENGTH) {
try {
id.fromString(path, pathPadding);
return true;
} catch (ArrayIndexOutOfBoundsException notHex) {
return false;
}
}
return false;
}

private FanoutBucket parseFanoutTree() {
final FanoutBucket fanout = new FanoutBucket(prefix.length());

for (; !eof(); next(1)) {
final int cell = parseFanoutCell();
if (0 <= cell)
fanout.parseOneEntry(cell, getEntryObjectId());
}

return fanout;
}

private int parseFanoutCell() {
if (getNameLength() == 2 && isTree()) {
try {
return (parseHexInt4(path[pathOffset + 0]) << 4)
| parseHexInt4(path[pathOffset + 1]);
} catch (ArrayIndexOutOfBoundsException notHex) {
return -1;
}
} else {
return -1;
}
}

private boolean isTree() {
return TREE.equals(mode);
}

private boolean isHex() {
try {
for (int i = pathOffset; i < pathLen; i++)
parseHexInt4(path[i]);
return true;
} catch (ArrayIndexOutOfBoundsException fail) {
return false;
}
}
}

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