org.eclipse.osgi.framework.eventmgr.CopyOnWriteIdentityMap Maven / Gradle / Ivy
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/*******************************************************************************
* Copyright (c) 2003, 2020 IBM Corporation and others.
*
* This program and the accompanying materials
* are made available under the terms of the Eclipse Public License 2.0
* which accompanies this distribution, and is available at
* https://www.eclipse.org/legal/epl-2.0/
*
* SPDX-License-Identifier: EPL-2.0
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.osgi.framework.eventmgr;
import static java.util.Objects.requireNonNull;
import java.util.AbstractCollection;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* A copy-on-write identity map. Write operations result in copying the underlying data so that
* simultaneous read operations are not affected.
* This allows for safe, unsynchronized traversal.
*
*
* Note: This class uses identity for key and value comparison, not equals.
*
* @since 3.5
*/
public class CopyOnWriteIdentityMap implements Map {
/**
* The empty array singleton instance.
*/
@SuppressWarnings("rawtypes")
private static final Entry[] emptyArray = new Entry[0];
/**
* The array of entries. This field is volatile so it can be
* accessed from unsynchronized reader methods.
*/
private volatile Entry[] entries;
/**
* Creates an empty map.
*
*/
public CopyOnWriteIdentityMap() {
entries = empty();
}
/**
* Copy constructor.
*
* @param source The CopyOnWriteMap to copy.
*/
public CopyOnWriteIdentityMap(CopyOnWriteIdentityMap source) {
@SuppressWarnings("unchecked")
Entry[] toCopy = (Entry[]) source.entries();
this.entries = toCopy;
}
/* These methods modify the map and are synchronized. */
/**
* Add a key, value pair to the map. If the key object is already in the map,
* then its value is replaced with the new value. Keys are compared using
* identity.
*
* @param key The key object to be added to the list.
* @param value The value object to be associated with the key. This may be
* null.
* @return null if the specified key was newly added to the map.
* Otherwise the previous value of the key.
* @throws NullPointerException If key is null.
*/
@Override
public synchronized V put(K key, V value) {
requireNonNull(key);
int size = entries.length;
for (int i = 0; i < size; i++) {
if (entries[i].key == key) {
V v = entries[i].value;
if (v == value) {
return v;
}
@SuppressWarnings("unchecked")
Entry[] newEntries = new Entry[size];
System.arraycopy(entries, 0, newEntries, 0, size);
newEntries[i] = new Entry<>(key, value);
entries = newEntries;
return v;
}
}
@SuppressWarnings("unchecked")
Entry[] newEntries = new Entry[size + 1];
if (size > 0) {
System.arraycopy(entries, 0, newEntries, 0, size);
}
newEntries[size] = new Entry<>(key, value);
entries = newEntries;
return null;
}
/**
* Add all the entries from the specified map to this map.
*
* @param source The map whose entries are to be added to this map.
*/
@Override
public void putAll(Map source) {
int sourceSize = source.size();
if (sourceSize == 0) {
return;
}
if (source instanceof CopyOnWriteIdentityMap) {
putAll(((CopyOnWriteIdentityMap) source).entries());
return;
}
@SuppressWarnings("unchecked")
Entry[] toCopy = new Entry[sourceSize];
Iterator> iter = source.entrySet().iterator();
for (int i = 0; i < sourceSize; i++) {
Map.Entry mapEntry = iter.next();
toCopy[i] = new Entry<>(mapEntry.getKey(), mapEntry.getValue());
}
putAll(toCopy);
}
/**
* Add all the keys from the specified array to this map with the value
* null.
*
* @param keys The array of keys to be added to this map.
*/
public void putAll(L[] keys) {
int sourceSize = keys.length;
if (sourceSize == 0) {
return;
}
@SuppressWarnings("unchecked")
Entry[] toCopy = new Entry[sourceSize];
for (int i = 0; i < sourceSize; i++) {
toCopy[i] = new Entry<>(keys[i], null);
}
putAll(toCopy);
}
/**
* Add all the entries to this map.
*
* @param toCopy Array of entries to add to this map.
*/
private synchronized void putAll(Entry[] toCopy) {
int sourceSize = toCopy.length;
int size = entries.length;
@SuppressWarnings("unchecked")
Entry[] newEntries = new Entry[size + sourceSize];
System.arraycopy(entries, 0, newEntries, 0, size);
copy: for (int n = 0; n < sourceSize; n++) {
@SuppressWarnings("unchecked")
Entry copy = (Entry) toCopy[n];
for (int i = 0; i < size; i++) {
if (newEntries[i].key == copy.key) {
newEntries[i] = copy;
continue copy;
}
}
newEntries[size] = copy;
size++;
}
if (size == newEntries.length) {
entries = newEntries;
return;
}
@SuppressWarnings("unchecked")
Entry[] e = new Entry[size];
System.arraycopy(newEntries, 0, e, 0, size);
entries = e;
}
/**
* Remove a key from the map and returns the value associated with the key. Key
* objects are compared using identity.
*
* @param key The key object to be removed from the map.
* @return null if the key was not in the list. Otherwise, the
* value associated with the key.
* @throws NullPointerException If key is null.
*/
@Override
public synchronized V remove(Object key) {
requireNonNull(key);
int size = entries.length;
for (int i = 0; i < size; i++) {
if (entries[i].key == key) {
V v = entries[i].value;
entries = removeEntry(entries, i);
return v;
}
}
return null;
}
/**
* Static method used to return an Entry array with the ith entry removed.
*/
static Entry[] removeEntry(final Entry[] entries, final int i) {
int size = entries.length;
if (size == 1) {
return empty();
}
@SuppressWarnings("unchecked")
Entry[] newEntries = new Entry[size - 1];
if (i > 0) {
System.arraycopy(entries, 0, newEntries, 0, i);
}
int next = size - 1 - i;
if (next > 0) {
System.arraycopy(entries, i + 1, newEntries, i, next);
}
return newEntries;
}
/**
* Remove all entries from the map.
*
*/
@Override
public synchronized void clear() {
entries = empty();
}
/* These methods only read the map and are not synchronized. */
/**
* Accessor for methods which only read the entries.
* @return The array of entries. Callers to this method MUST NOT
* modify the returned array.
*/
private Entry[] entries() {
return entries;
}
/**
* Return the static empty array generically type safe.
* @return The empty array of entries.
*/
@SuppressWarnings("unchecked")
static Entry[] empty() {
return emptyArray;
}
/**
* Is the map empty?
*
* @return true if the list is empty.
*/
@Override
public boolean isEmpty() {
return size() == 0;
}
/**
* Return the number of entries in the map.
*
* @return The number of entries in the map.
*/
@Override
public int size() {
return entries().length;
}
/**
* Return the value object for the specified key. Keys are compared using
* identity.
*
* @param key The key object.
* @return The value object for the specified key.
* @throws NullPointerException If key is null.
*/
@Override
public V get(Object key) {
requireNonNull(key);
for (Entry entry : entries()) {
if (entry.key == key) {
return entry.value;
}
}
return null;
}
/**
* Check if the map contains the specified key. Keys are compared using
* identity.
*
* @param key The key object.
* @return true if the specified key is in the map.
* @throws NullPointerException If key is null.
*/
@Override
public boolean containsKey(Object key) {
requireNonNull(key);
for (Entry entry : entries()) {
if (entry.key == key) {
return true;
}
}
return false;
}
/**
* Check if the map contains the specified value.
* Values are compared using identity.
*
* @param value The value object.
* @return true if the specified value is in the map.
*/
@Override
public boolean containsValue(Object value) {
for (Entry entry : entries()) {
if (entry.value == value) {
return true;
}
}
return false;
}
/**
* Returns a snapshot of the entries in this map.
* Changes to the returned set or this map will not affect each other.
*
* @return A Set of Map.Entry for each entry in this map.
* The entries returned by the set cannot be modified.
*/
@Override
public Set> entrySet() {
return new Snapshot<>(entries()).entrySet();
}
/**
* Returns a snapshot of the keys in this map.
* Changes to the returned set or this map will not affect each other.
*
* @return A Set of the key objects in this map
*/
@Override
public Set keySet() {
return new Snapshot<>(entries()).keySet();
}
/**
* Returns a snapshot of the values in this map.
* Changes to the returned set or this map will not affect each other.
*
* @return A Collection of the value objects in this map.
*/
@Override
public Collection values() {
return new Snapshot<>(entries()).values();
}
/**
* This class represents the entry in this identity map.
* Entry is immutable.
*/
static private final class Entry implements Map.Entry {
/**
* Key object.
*/
final K key;
/**
* Value object.
*/
final V value;
/**
* Constructor for map entry.
*
* @param key Key object in entry. Used for uniqueness.
* @param value Value object stored with key object.
* @throws NullPointerException If key is null.
*/
Entry(final K key, final V value) {
this.key = requireNonNull(key);
this.value = value;
}
@Override
public K getKey() {
return key;
}
@Override
public V getValue() {
return value;
}
@Override
public V setValue(V value) {
throw new UnsupportedOperationException(); // entries cannot be modified.
}
@Override
public String toString() {
return key + "=" + value; //$NON-NLS-1$
}
@Override
public int hashCode() {
return System.identityHashCode(key) ^ System.identityHashCode(value);
}
@Override
public boolean equals(Object obj) {
if (obj == this) {
return true;
}
if (!(obj instanceof Map.Entry)) {
return false;
}
Map.Entry e = (Map.Entry) obj;
return (key == e.getKey()) && (value == e.getValue());
}
}
/**
* A snapshot of the entries in the map. This snapshot used by
* the map collection views. Changes made by the collection
* views only mutate the snapshot and not the map. The collection
* views only allow removal not addition.
*/
static private final class Snapshot {
volatile Entry[] entries;
Snapshot(Entry[] e) {
entries = e;
}
Entry[] entries() {
return entries;
}
synchronized void removeEntry(int i) {
entries = CopyOnWriteIdentityMap.removeEntry(entries, i);
}
synchronized void clearEntries() {
entries = CopyOnWriteIdentityMap.empty();
}
Set> entrySet() {
return new EntrySet();
}
Set keySet() {
return new KeySet();
}
Collection values() {
return new ValueCollection();
}
/**
* Entry set view over the snapshot.
*/
private final class EntrySet extends AbstractSet> {
EntrySet() {
super();
}
@Override
public Iterator> iterator() {
return new EntryIterator();
}
@Override
public int size() {
return entries().length;
}
@Override
public boolean remove(Object o) {
requireNonNull(o);
synchronized (Snapshot.this) {
int size = entries.length;
for (int i = 0; i < size; i++) {
if (entries[i].equals(o)) {
removeEntry(i);
return true;
}
}
}
return false;
}
@Override
public void clear() {
clearEntries();
}
}
/**
* Entry set iterator over the snapshot.
*/
private final class EntryIterator extends SnapshotIterator> {
EntryIterator() {
super();
}
@Override
public Map.Entry next() {
return nextEntry();
}
}
/**
* Key set view over the snapshot.
*/
private final class KeySet extends AbstractSet {
KeySet() {
super();
}
@Override
public Iterator iterator() {
return new KeyIterator();
}
@Override
public int size() {
return entries().length;
}
@Override
public boolean remove(Object o) {
requireNonNull(o);
synchronized (Snapshot.this) {
int size = entries.length;
for (int i = 0; i < size; i++) {
if (entries[i].key == o) {
removeEntry(i);
return true;
}
}
}
return false;
}
@Override
public void clear() {
clearEntries();
}
}
/**
* Key set iterator over the snapshot.
*/
private final class KeyIterator extends SnapshotIterator {
KeyIterator() {
super();
}
@Override
public K next() {
return nextEntry().key;
}
}
/**
* Value collection view over the snapshot.
*/
private final class ValueCollection extends AbstractCollection {
ValueCollection() {
super();
}
@Override
public Iterator iterator() {
return new ValueIterator();
}
@Override
public int size() {
return entries().length;
}
@Override
public boolean remove(Object o) {
requireNonNull(o);
synchronized (Snapshot.this) {
int size = entries.length;
for (int i = 0; i < size; i++) {
if (entries[i].value == o) {
removeEntry(i);
return true;
}
}
}
return false;
}
@Override
public void clear() {
clearEntries();
}
}
/**
* Value collection iterator over the snapshot.
*/
private final class ValueIterator extends SnapshotIterator {
ValueIterator() {
super();
}
@Override
public V next() {
return nextEntry().value;
}
}
/**
* Base iterator class handling removal and concurrent modifications.
*/
private abstract class SnapshotIterator implements Iterator {
private int length;
private int cursor;
SnapshotIterator() {
length = entries().length;
cursor = 0;
}
@Override
public final boolean hasNext() {
return cursor < length;
}
protected final Entry nextEntry() {
Entry[] e = entries();
if (length != e.length) {
throw new ConcurrentModificationException();
}
if (cursor == length) {
throw new NoSuchElementException();
}
return e[cursor++];
}
@Override
public final void remove() {
if (length != entries().length) {
throw new ConcurrentModificationException();
}
if (cursor == 0) {
throw new IllegalStateException();
}
cursor--;
removeEntry(cursor);
length = entries().length;
}
}
}
}