ObjectIdSubclassMap.java
/*
* Copyright (C) 2009, Google Inc.
* Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
* Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
* 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,
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package org.eclipse.jgit.lib;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Fast, efficient map specifically for {@link org.eclipse.jgit.lib.ObjectId}
* subclasses.
* <p>
* This map provides an efficient translation from any ObjectId instance to a
* cached subclass of ObjectId that has the same value.
* <p>
* If object instances are stored in only one map,
* {@link org.eclipse.jgit.lib.ObjectIdOwnerMap} is a more efficient
* implementation.
*
* @param <V>
* type of subclass of ObjectId that will be stored in the map.
*/
public class ObjectIdSubclassMap<V extends ObjectId>
implements Iterable<V>, ObjectIdSet {
private static final int INITIAL_TABLE_SIZE = 2048;
int size;
private int grow;
private int mask;
V[] table;
/**
* Create an empty map.
*/
public ObjectIdSubclassMap() {
initTable(INITIAL_TABLE_SIZE);
}
/**
* Remove all entries from this map.
*/
public void clear() {
size = 0;
initTable(INITIAL_TABLE_SIZE);
}
/**
* Lookup an existing mapping.
*
* @param toFind
* the object identifier to find.
* @return the instance mapped to toFind, or null if no mapping exists.
*/
public V get(AnyObjectId toFind) {
final int msk = mask;
int i = toFind.w1 & msk;
final V[] tbl = table;
V obj;
while ((obj = tbl[i]) != null) {
if (AnyObjectId.equals(obj, toFind))
return obj;
i = (i + 1) & msk;
}
return null;
}
/**
* {@inheritDoc}
* <p>
* Returns true if this map contains the specified object.
*/
@Override
public boolean contains(AnyObjectId toFind) {
return get(toFind) != null;
}
/**
* Store an object for future lookup.
* <p>
* An existing mapping for <b>must not</b> 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(ObjectId)}.
*
* @param newValue
* the object to store.
*/
public <Q extends V> void add(Q newValue) {
if (++size == grow)
grow();
insert(newValue);
}
/**
* Store an object for future lookup.
* <p>
* 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:
*
* <pre>
* V obj = ...;
* boolean wasNew = map.addIfAbsent(obj) == obj;
* </pre>
*
* @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.
*/
public <Q extends V> V addIfAbsent(Q newValue) {
final int msk = mask;
int i = newValue.w1 & msk;
final V[] tbl = table;
V obj;
while ((obj = tbl[i]) != null) {
if (AnyObjectId.equals(obj, newValue))
return obj;
i = (i + 1) & msk;
}
if (++size == grow) {
grow();
insert(newValue);
} else {
tbl[i] = newValue;
}
return newValue;
}
/**
* Get number of objects in map
*
* @return number of objects in map
*/
public int size() {
return size;
}
/**
* Whether {@link #size()} is 0.
*
* @return true if {@link #size()} is 0.
*/
public boolean isEmpty() {
return size == 0;
}
/** {@inheritDoc} */
@Override
public Iterator<V> iterator() {
return new Iterator<V>() {
private int found;
private int i;
@Override
public boolean hasNext() {
return found < size;
}
@Override
public V next() {
while (i < table.length) {
final V v = table[i++];
if (v != null) {
found++;
return v;
}
}
throw new NoSuchElementException();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
private void insert(V newValue) {
final int msk = mask;
int j = newValue.w1 & msk;
final V[] tbl = table;
while (tbl[j] != null)
j = (j + 1) & msk;
tbl[j] = newValue;
}
private void grow() {
final V[] oldTable = table;
final int oldSize = table.length;
initTable(oldSize << 1);
for (int i = 0; i < oldSize; i++) {
final V obj = oldTable[i];
if (obj != null)
insert(obj);
}
}
private void initTable(int sz) {
grow = sz >> 1;
mask = sz - 1;
table = createArray(sz);
}
@SuppressWarnings("unchecked")
private final V[] createArray(int sz) {
return (V[]) new ObjectId[sz];
}
}