org.eclipse.jgit.lib.ObjectIdOwnerMap Maven / Gradle / Ivy
/*
* Copyright (C) 2011, 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
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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package org.eclipse.jgit.lib;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Fast, efficient map for {@link ObjectId} subclasses in only one map.
*
* To use this map type, applications must have their entry value type extend
* from {@link ObjectIdOwnerMap.Entry}, which itself extends from ObjectId.
*
* Object instances may only be stored in ONE ObjectIdOwnerMap. This
* restriction exists because the map stores internal map state within each
* object instance. If an instance is be placed in another ObjectIdOwnerMap it
* could corrupt one or both map's internal state.
*
* If an object instance must be in more than one map, applications may use
* ObjectIdOwnerMap for one of the maps, and {@link ObjectIdSubclassMap} for the
* other map(s). It is encouraged to use ObjectIdOwnerMap for the map that is
* accessed most often, as this implementation runs faster than the more general
* ObjectIdSubclassMap implementation.
*
* @param
* type of subclass of ObjectId that will be stored in the map.
*/
public class ObjectIdOwnerMap implements
Iterable {
/** Size of the initial directory, will grow as necessary. */
private static final int INITIAL_DIRECTORY = 1024;
/** Number of bits in a segment's index. Segments are 2^11 in size. */
private static final int SEGMENT_BITS = 11;
private static final int SEGMENT_SHIFT = 32 - SEGMENT_BITS;
/**
* Top level directory of the segments.
*
* The low {@link #bits} of the SHA-1 are used to select the segment from
* this directory. Each segment is constant sized at 2^SEGMENT_BITS.
*/
private V[][] directory;
/** Total number of objects in this map. */
private int size;
/** The map doubles in capacity when {@link #size} reaches this target. */
private int grow;
/** Number of low bits used to form the index into {@link #directory}. */
private int bits;
/** Low bit mask to index into {@link #directory}, {@code 2^bits-1}. */
private int mask;
/** Create an empty map. */
@SuppressWarnings("unchecked")
public ObjectIdOwnerMap() {
bits = 0;
mask = 0;
grow = computeGrowAt(bits);
directory = (V[][]) new Entry[INITIAL_DIRECTORY][];
directory[0] = newSegment();
}
/** Remove all entries from this map. */
public void clear() {
size = 0;
for (V[] tbl : directory) {
if (tbl == null)
break;
Arrays.fill(tbl, null);
}
}
/**
* Lookup an existing mapping.
*
* @param toFind
* the object identifier to find.
* @return the instance mapped to toFind, or null if no mapping exists.
*/
@SuppressWarnings("unchecked")
public V get(final AnyObjectId toFind) {
int h = toFind.w1;
V obj = directory[h & mask][h >>> SEGMENT_SHIFT];
for (; obj != null; obj = (V) obj.next)
if (equals(obj, toFind))
return obj;
return null;
}
/**
* Returns true if this map contains the specified object.
*
* @param toFind
* object to find.
* @return true if the mapping exists for this object; false otherwise.
*/
public boolean contains(final AnyObjectId toFind) {
return get(toFind) != null;
}
/**
* Store an object for future lookup.
*
* An existing mapping for must not be in this map. Callers must
* first call {@link #get(AnyObjectId)} to verify there is no current
* mapping prior to adding a new mapping, or use {@link #addIfAbsent(Entry)}.
*
* @param newValue
* the object to store.
* @param
* type of instance to store.
*/
public void add(final Q newValue) {
if (++size == grow)
grow();
int h = newValue.w1;
V[] table = directory[h & mask];
h >>>= SEGMENT_SHIFT;
newValue.next = table[h];
table[h] = newValue;
}
/**
* Store an object for future lookup.
*
* Stores {@code newValue}, but only if there is not already an object for
* the same object name. Callers can tell if the value is new by checking
* the return value with reference equality:
*
*
* V obj = ...;
* boolean wasNew = map.addIfAbsent(obj) == obj;
*
*
* @param newValue
* the object to store.
* @return {@code newValue} if stored, or the prior value already stored and
* that would have been returned had the caller used
* {@code get(newValue)} first.
* @param
* type of instance to store.
*/
@SuppressWarnings("unchecked")
public V addIfAbsent(final Q newValue) {
int h = newValue.w1;
V[] table = directory[h & mask];
h >>>= SEGMENT_SHIFT;
for (V obj = table[h]; obj != null; obj = (V) obj.next)
if (equals(obj, newValue))
return obj;
newValue.next = table[h];
table[h] = newValue;
if (++size == grow)
grow();
return newValue;
}
/** @return number of objects in this map. */
public int size() {
return size;
}
/** @return true if {@link #size()} is 0. */
public boolean isEmpty() {
return size == 0;
}
public Iterator iterator() {
return new Iterator() {
private int found;
private int dirIdx;
private int tblIdx;
private V next;
public boolean hasNext() {
return found < size;
}
public V next() {
if (next != null)
return found(next);
for (;;) {
V[] table = directory[dirIdx];
if (tblIdx == table.length) {
if (++dirIdx >= (1 << bits))
throw new NoSuchElementException();
table = directory[dirIdx];
tblIdx = 0;
}
while (tblIdx < table.length) {
V v = table[tblIdx++];
if (v != null)
return found(v);
}
}
}
@SuppressWarnings("unchecked")
private V found(V v) {
found++;
next = (V) v.next;
return v;
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@SuppressWarnings("unchecked")
private void grow() {
final int oldDirLen = 1 << bits;
final int s = 1 << bits;
bits++;
mask = (1 << bits) - 1;
grow = computeGrowAt(bits);
// Quadruple the directory if it needs to expand. Expanding the
// directory is expensive because it generates garbage, so try
// to avoid doing it often.
//
final int newDirLen = 1 << bits;
if (directory.length < newDirLen) {
V[][] newDir = (V[][]) new Entry[newDirLen << 1][];
System.arraycopy(directory, 0, newDir, 0, oldDirLen);
directory = newDir;
}
// For every bucket of every old segment, split the chain between
// the old segment and the new segment's corresponding bucket. To
// select between them use the lowest bit that was just added into
// the mask above. This causes the table to double in capacity.
//
for (int dirIdx = 0; dirIdx < oldDirLen; dirIdx++) {
final V[] oldTable = directory[dirIdx];
final V[] newTable = newSegment();
for (int i = 0; i < oldTable.length; i++) {
V chain0 = null;
V chain1 = null;
V next;
for (V obj = oldTable[i]; obj != null; obj = next) {
next = (V) obj.next;
if ((obj.w1 & s) == 0) {
obj.next = chain0;
chain0 = obj;
} else {
obj.next = chain1;
chain1 = obj;
}
}
oldTable[i] = chain0;
newTable[i] = chain1;
}
directory[oldDirLen + dirIdx] = newTable;
}
}
@SuppressWarnings("unchecked")
private final V[] newSegment() {
return (V[]) new Entry[1 << SEGMENT_BITS];
}
private static final int computeGrowAt(int bits) {
return 1 << (bits + SEGMENT_BITS);
}
private static final boolean equals(AnyObjectId firstObjectId,
AnyObjectId secondObjectId) {
return firstObjectId.w2 == secondObjectId.w2
&& firstObjectId.w3 == secondObjectId.w3
&& firstObjectId.w4 == secondObjectId.w4
&& firstObjectId.w5 == secondObjectId.w5
&& firstObjectId.w1 == secondObjectId.w1;
}
/** Type of entry stored in the {@link ObjectIdOwnerMap}. */
public static abstract class Entry extends ObjectId {
Entry next;
/**
* Initialize this entry with a specific ObjectId.
*
* @param id
* the id the entry represents.
*/
public Entry(AnyObjectId id) {
super(id);
}
}
}