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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to you under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.logging.log4j.internal.map;
import java.io.Serializable;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import org.apache.logging.log4j.util.ReadOnlyStringMap;
import org.apache.logging.log4j.util.TriConsumer;
/**
* This class represents an immutable map, which stores its state inside a single Object[]:
*
*
[0] contains the number of entries
*
Others contain alternating key-value pairs, for example [1]="1" and [2]="value_for_1"
*
*
* Keys are calculated using (index * 2 + 1) and values are (index * 2 + 2).
*
* Performance:
*
*
Implements very low-cost copies: shallow-copy the array.
*
Doesn't matter for mutable operations, since we don't allow them.
*
Iterates very quickly, since it iterates directly across the array. This
* contrasts with HashMap's requirement to scan each bucket in the table and
* chase each pointer.
*
Is linear on gets, puts, and removes, since the table must be scanned to
* find a matching key.
*
*
* Allocation:
*
*
Zero on reads.
*
Copy-and-modify operations allocate exactly two objects: the new array
* and the new Map instance. This is substantially better than HashMap, which
* requires a new Node for each entry.
*
*
*/
public class UnmodifiableArrayBackedMap extends AbstractMap implements Serializable, ReadOnlyStringMap {
/**
* Implementation of Map.Entry. The implementation is simple since each instance
* contains an index in the array, then getKey() and getValue() retrieve from
* the array. Blocks modifications.
*/
private class UnmodifiableEntry implements Map.Entry {
/**
* This field is functionally final, but marking it as such can cause
* performance problems. Consider marking it final after
* https://bugs.openjdk.org/browse/JDK-8324186 is solved.
*/
private int index;
public UnmodifiableEntry(int index) {
this.index = index;
}
@Override
public String getKey() {
return (String) backingArray[getArrayIndexForKey(index)];
}
@Override
public String getValue() {
return (String) backingArray[getArrayIndexForValue(index)];
}
/**
* Per spec, the hashcode is a function of the key and value. Calculation
* exactly matches HashMap.
*/
public int hashCode() {
String key = (String) backingArray[getArrayIndexForKey(index)];
String value = (String) backingArray[getArrayIndexForValue(index)];
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
@Override
public String setValue(String value) {
throw new UnsupportedOperationException("Cannot update Entry instances in UnmodifiableArrayBackedMap");
}
}
/**
* Simple Entry iterator, tracking solely the index in the array. Blocks
* modifications.
*/
private class UnmodifiableEntryIterator implements Iterator> {
private int index;
@Override
public boolean hasNext() {
return index < numEntries;
}
@Override
public Entry next() {
return new UnmodifiableEntry(index++);
}
}
/**
* Simple Entry set, providing a reference to UnmodifiableEntryIterator and
* blocking modifications.
*/
private class UnmodifiableEntrySet extends AbstractSet> {
@Override
public boolean add(Entry e) {
throw new UnsupportedOperationException();
}
@Override
public boolean addAll(Collection> c) {
throw new UnsupportedOperationException();
}
@Override
public Iterator> iterator() {
return new UnmodifiableEntryIterator();
}
@Override
public int size() {
return numEntries;
}
}
private static final long serialVersionUID = 6849423432534211514L;
public static final UnmodifiableArrayBackedMap EMPTY_MAP = new UnmodifiableArrayBackedMap(0);
private static final int NUM_FIXED_ARRAY_ENTRIES = 1;
private static int getArrayIndexForKey(int entryIndex) {
return 2 * entryIndex + NUM_FIXED_ARRAY_ENTRIES;
}
private static int getArrayIndexForValue(int entryIndex) {
return 2 * entryIndex + 1 + NUM_FIXED_ARRAY_ENTRIES;
}
public static UnmodifiableArrayBackedMap getMap(Object[] backingArray) {
if (backingArray == null || backingArray.length == 1) {
return EMPTY_MAP;
} else {
return new UnmodifiableArrayBackedMap(backingArray);
}
}
/**
* backingArray is functionally final, but marking it as such can cause
* performance problems. Consider marking it final after
* https://bugs.openjdk.org/browse/JDK-8324186 is solved.
*/
private Object[] backingArray;
private int numEntries;
private UnmodifiableArrayBackedMap(int capacity) {
this.backingArray = new Object[capacity * 2 + 1];
this.backingArray[0] = 0;
}
private UnmodifiableArrayBackedMap(Object[] backingArray) {
this.numEntries = (backingArray == null ? 0 : (int) backingArray[0]);
this.backingArray = backingArray;
}
UnmodifiableArrayBackedMap(UnmodifiableArrayBackedMap other) {
this.backingArray = other.backingArray;
this.numEntries = other.numEntries;
}
private void add(String key, String value) {
backingArray[getArrayIndexForKey(numEntries)] = key;
backingArray[getArrayIndexForValue(numEntries)] = value;
numEntries++;
}
@Override
public void clear() {
throw new UnsupportedOperationException("Instance cannot be cleared, reuse EMPTY_MAP instead.");
}
/**
* Scans the array to find a matching key. Linear performance.
*/
@Override
public boolean containsKey(Object key) {
return containsKey((String) key);
}
@Override
public boolean containsKey(String key) {
int hashCode = key.hashCode();
for (int i = 0; i < numEntries; i++) {
if (backingArray[getArrayIndexForKey(i)].hashCode() == hashCode
&& backingArray[getArrayIndexForKey(i)].equals(key)) {
return true;
}
}
return false;
}
public Object[] getBackingArray() {
return backingArray;
}
/**
* Scans the array to find a matching value, with linear time. Allows null
* parameter.
*/
@Override
public boolean containsValue(Object value) {
for (int i = 0; i < numEntries; i++) {
Object valueInMap = backingArray[getArrayIndexForValue(i)];
if (value == null) {
if (valueInMap == null) {
return true;
}
} else if (value.equals(valueInMap)) {
return true;
}
}
return false;
}
/**
* Creates a new instance that contains the same entries as this map, plus
* either the new entry or updated value passed in the parameters.
*
* @param key
* @param value
* @return
*/
public UnmodifiableArrayBackedMap copyAndPut(String key, String value) {
UnmodifiableArrayBackedMap newMap = new UnmodifiableArrayBackedMap(numEntries + 1);
// include the numEntries value (array index 0)
if (this.numEntries > 0) {
System.arraycopy(this.backingArray, 1, newMap.backingArray, 1, numEntries * 2);
newMap.numEntries = numEntries;
}
newMap.addOrOverwriteKey(key, value);
newMap.updateNumEntriesInArray();
return newMap;
}
/**
* Creates a new instance that contains the same entries as this map, plus the
* new entries or updated values passed in the parameters.
*
* @param key
* @param value
* @return
*/
public UnmodifiableArrayBackedMap copyAndPutAll(Map entriesToAdd) {
// create a new array that can hold the maximum output size
UnmodifiableArrayBackedMap newMap = new UnmodifiableArrayBackedMap(numEntries + entriesToAdd.size());
// copy the contents of the current map (if any)
if (numEntries > 0) {
System.arraycopy(backingArray, 0, newMap.backingArray, 0, numEntries * 2 + 1);
}
for (Map.Entry entry : entriesToAdd.entrySet()) {
String key = entry.getKey();
String value = entry.getValue();
if (!this.isEmpty()) {
// The unique elements passed in may overlap the unique elements here - must
// check
newMap.addOrOverwriteKey(key, value);
} else {
// There is no chance of overlapping keys, we can simply add
newMap.add(key, value);
}
}
newMap.updateNumEntriesInArray();
return newMap;
}
/**
* Creates a new instance that contains the same entries as this map, minus the
* entry with the specified key (if such an entry exists).
*
* @param key
* @param value
* @return
*/
public UnmodifiableArrayBackedMap copyAndRemove(String key) {
int indexToRemove = -1;
for (int oldIndex = numEntries - 1; oldIndex >= 0; oldIndex--) {
if (backingArray[getArrayIndexForKey(oldIndex)].hashCode() == key.hashCode()
&& backingArray[getArrayIndexForKey(oldIndex)].equals(key)) {
indexToRemove = oldIndex;
break;
}
}
if (indexToRemove == -1) {
// key not found, no change necessary
return this;
} else if (numEntries == 1) {
// we have 1 item and we're about to remove it
return EMPTY_MAP;
}
UnmodifiableArrayBackedMap newMap = new UnmodifiableArrayBackedMap(numEntries);
if (indexToRemove > 0) {
// copy entries before the removed one
System.arraycopy(backingArray, 1, newMap.backingArray, 1, indexToRemove * 2);
}
if (indexToRemove + 1 < numEntries) {
// copy entries after the removed one
int nextIndexToCopy = indexToRemove + 1;
int numRemainingEntries = numEntries - nextIndexToCopy;
System.arraycopy(
backingArray,
getArrayIndexForKey(nextIndexToCopy),
newMap.backingArray,
getArrayIndexForKey(indexToRemove),
numRemainingEntries * 2);
}
newMap.numEntries = numEntries - 1;
newMap.updateNumEntriesInArray();
return newMap;
}
/**
* Creates a new instance that contains the same entries as this map, minus all
* of the keys passed in the arguments.
*
* @param key
* @param value
* @return
*/
public UnmodifiableArrayBackedMap copyAndRemoveAll(Iterable keysToRemoveIterable) {
if (isEmpty()) {
// shortcut: if this map is empty, the result will continue to be empty
return EMPTY_MAP;
}
// now we build a Set of keys to remove
Set keysToRemoveSet;
if (keysToRemoveIterable instanceof Set) {
// we already have a set, let's cast it and reuse it
keysToRemoveSet = (Set) keysToRemoveIterable;
} else {
// iterate through the keys and build a set
keysToRemoveSet = new HashSet<>();
for (String key : keysToRemoveIterable) {
keysToRemoveSet.add(key);
}
}
int firstIndexToKeep = -1;
int lastIndexToKeep = -1;
int destinationIndex = 0;
int numEntriesKept = 0;
// build the new map
UnmodifiableArrayBackedMap newMap = new UnmodifiableArrayBackedMap(numEntries);
for (int indexInCurrentMap = 0; indexInCurrentMap < numEntries; indexInCurrentMap++) {
// for each key in this map, check whether it's in the set we built above
Object key = backingArray[getArrayIndexForKey(indexInCurrentMap)];
if (!keysToRemoveSet.contains(key)) {
// this key should be kept
if (firstIndexToKeep == -1) {
firstIndexToKeep = indexInCurrentMap;
}
lastIndexToKeep = indexInCurrentMap;
} else if (lastIndexToKeep > 0) {
// we hit a remove, copy any keys that are known ready
int numEntriesToCopy = lastIndexToKeep - firstIndexToKeep + 1;
System.arraycopy(
backingArray,
getArrayIndexForKey(firstIndexToKeep),
newMap.backingArray,
getArrayIndexForKey(destinationIndex),
numEntriesToCopy * 2);
firstIndexToKeep = -1;
lastIndexToKeep = -1;
destinationIndex += numEntriesToCopy;
numEntriesKept += numEntriesToCopy;
}
}
if (lastIndexToKeep > -1) {
// at least one key still requires copying
int numEntriesToCopy = lastIndexToKeep - firstIndexToKeep + 1;
System.arraycopy(
backingArray,
getArrayIndexForKey(firstIndexToKeep),
newMap.backingArray,
getArrayIndexForKey(destinationIndex),
numEntriesToCopy * 2);
numEntriesKept += numEntriesToCopy;
}
if (numEntriesKept == 0) {
return EMPTY_MAP;
}
newMap.numEntries = numEntriesKept;
newMap.updateNumEntriesInArray();
return newMap;
}
/**
* Copies the locally-tracked numEntries into the first array slot. Requires
* autoboxing so call should be minimized - for example, once per bulk update
* operation.
*/
private void updateNumEntriesInArray() {
backingArray[0] = numEntries;
}
/**
* This version of forEach is defined on the Map interface.
*/
@Override
public void forEach(java.util.function.BiConsumer action) {
for (int i = 0; i < numEntries; i++) {
// BiConsumer should be able to handle values of any type V. In our case the values are of type String.
final String key = (String) backingArray[getArrayIndexForKey(i)];
final String value = (String) backingArray[getArrayIndexForValue(i)];
action.accept(key, value);
}
}
/**
* This version of forEach is defined on the ReadOnlyStringMap interface.
*/
@SuppressWarnings("unchecked")
@Override
public void forEach(final org.apache.logging.log4j.util.BiConsumer action) {
for (int i = 0; i < numEntries; i++) {
// BiConsumer should be able to handle values of any type V. In our case the values are of type String.
final String key = (String) backingArray[getArrayIndexForKey(i)];
final V value = (V) backingArray[getArrayIndexForValue(i)];
action.accept(key, value);
}
}
@SuppressWarnings("unchecked")
public void forEach(final TriConsumer action, final S state) {
for (int i = 0; i < numEntries; i++) {
// TriConsumer should be able to handle values of any type V. In our case the values are of type String.
final String key = (String) backingArray[getArrayIndexForKey(i)];
final V value = (V) backingArray[getArrayIndexForValue(i)];
action.accept(key, value, state);
}
}
@Override
public Set> entrySet() {
return new UnmodifiableEntrySet();
}
/**
* Scans the array to find a matching key. Linear-time.
*/
@Override
public String get(Object key) {
return getValue((String) key);
}
@SuppressWarnings("unchecked")
@Override
public V getValue(String key) {
if (numEntries == 0) {
return null;
}
int hashCode = key.hashCode();
for (int i = 0; i < numEntries; i++) {
if (backingArray[getArrayIndexForKey(i)].hashCode() == hashCode
&& backingArray[getArrayIndexForKey(i)].equals(key)) {
return (V) backingArray[getArrayIndexForValue(i)];
}
}
return null;
}
/**
* Find an existing entry (if any) and overwrites the value, if found
*
* @param key
* @param value
* @return
*/
private void addOrOverwriteKey(String key, String value) {
int keyHashCode = key.hashCode();
for (int i = 0; i < numEntries; i++) {
if (backingArray[getArrayIndexForKey(i)].hashCode() == keyHashCode
&& backingArray[getArrayIndexForKey(i)].equals(key)) {
// found a match, overwrite then return
backingArray[getArrayIndexForValue(i)] = value;
return;
}
}
// no match found, add to the end
add(key, value);
}
@Override
public String put(String key, String value) {
throw new UnsupportedOperationException("put() is not supported, use copyAndPut instead");
}
@Override
public void putAll(Map m) {
throw new UnsupportedOperationException("putAll() is not supported, use copyAndPutAll instead");
}
@Override
public String remove(Object key) {
throw new UnsupportedOperationException("remove() is not supported, use copyAndRemove instead");
}
@Override
public int size() {
return numEntries;
}
@Override
public Map toMap() {
return this;
}
}
