/*
* 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.commons.collections4.map;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import org.apache.commons.collections4.MapIterator;
import org.apache.commons.collections4.keyvalue.DefaultMapEntry;
/**
* An abstract implementation of a hash-based map that allows the entries to
* be removed by the garbage collector.
*
* This class implements all the features necessary for a subclass reference
* hash-based map. Key-value entries are stored in instances of the
* ReferenceEntry class which can be overridden and replaced.
* The iterators can similarly be replaced, without the need to replace the KeySet,
* EntrySet and Values view classes.
*
* Overridable methods are provided to change the default hashing behaviour, and
* to change how entries are added to and removed from the map. Hopefully, all you
* need for unusual subclasses is here.
*
* When you construct an AbstractReferenceMap, you can specify what
* kind of references are used to store the map's keys and values.
* If non-hard references are used, then the garbage collector can remove
* mappings if a key or value becomes unreachable, or if the JVM's memory is
* running low. For information on how the different reference types behave,
* see {@link Reference}.
*
* Different types of references can be specified for keys and values.
* The keys can be configured to be weak but the values hard,
* in which case this class will behave like a
*
* WeakHashMap . However, you can also specify hard keys and
* weak values, or any other combination. The default constructor uses
* hard keys and soft values, providing a memory-sensitive cache.
*
* This {@link Map} implementation does not allow null elements.
* Attempting to add a null key or value to the map will raise a
* NullPointerException.
*
* All the available iterators can be reset back to the start by casting to
* ResettableIterator and calling reset().
*
* This implementation is not synchronized.
* You can use {@link java.util.Collections#synchronizedMap} to
* provide synchronized access to a ReferenceMap.
*
* @see java.lang.ref.Reference
* @since 3.1 (extracted from ReferenceMap in 3.0)
* @version $Id: AbstractReferenceMap.java 1477799 2013-04-30 19:56:11Z tn $
*/
public abstract class AbstractReferenceMap extends AbstractHashedMap {
/**
* Reference type enum.
*/
public static enum ReferenceStrength {
HARD(0), SOFT(1), WEAK(2);
/** value */
public final int value;
/**
* Resolve enum from int.
* @param value the int value
* @return ReferenceType
* @throws IllegalArgumentException if the specified value is invalid.
*/
public static ReferenceStrength resolve(final int value) {
switch (value) {
case 0:
return HARD;
case 1:
return SOFT;
case 2:
return WEAK;
default:
throw new IllegalArgumentException();
}
}
private ReferenceStrength(final int value) {
this.value = value;
}
}
/**
* The reference type for keys.
*/
private ReferenceStrength keyType;
/**
* The reference type for values.
*/
private ReferenceStrength valueType;
/**
* Should the value be automatically purged when the associated key has been collected?
*/
private boolean purgeValues;
/**
* ReferenceQueue used to eliminate stale mappings.
* See purge.
*/
private transient ReferenceQueue queue;
//-----------------------------------------------------------------------
/**
* Constructor used during deserialization.
*/
protected AbstractReferenceMap() {
super();
}
/**
* Constructs a new empty map with the specified reference types,
* load factor and initial capacity.
*
* @param keyType the type of reference to use for keys;
* must be {@link ReferenceStrength#HARD HARD},
* {@link ReferenceStrength#SOFT SOFT},
* {@link ReferenceStrength#WEAK WEAK}
* @param valueType the type of reference to use for values;
* must be {@link ReferenceStrength#HARD},
* {@link ReferenceStrength#SOFT SOFT},
* {@link ReferenceStrength#WEAK WEAK}
* @param capacity the initial capacity for the map
* @param loadFactor the load factor for the map
* @param purgeValues should the value be automatically purged when the
* key is garbage collected
*/
protected AbstractReferenceMap(
final ReferenceStrength keyType, final ReferenceStrength valueType, final int capacity,
final float loadFactor, final boolean purgeValues) {
super(capacity, loadFactor);
this.keyType = keyType;
this.valueType = valueType;
this.purgeValues = purgeValues;
}
/**
* Initialise this subclass during construction, cloning or deserialization.
*/
@Override
protected void init() {
queue = new ReferenceQueue();
}
//-----------------------------------------------------------------------
/**
* Gets the size of the map.
*
* @return the size
*/
@Override
public int size() {
purgeBeforeRead();
return super.size();
}
/**
* Checks whether the map is currently empty.
*
* @return true if the map is currently size zero
*/
@Override
public boolean isEmpty() {
purgeBeforeRead();
return super.isEmpty();
}
/**
* Checks whether the map contains the specified key.
*
* @param key the key to search for
* @return true if the map contains the key
*/
@Override
public boolean containsKey(final Object key) {
purgeBeforeRead();
final Entry entry = getEntry(key);
if (entry == null) {
return false;
}
return entry.getValue() != null;
}
/**
* Checks whether the map contains the specified value.
*
* @param value the value to search for
* @return true if the map contains the value
*/
@Override
public boolean containsValue(final Object value) {
purgeBeforeRead();
if (value == null) {
return false;
}
return super.containsValue(value);
}
/**
* Gets the value mapped to the key specified.
*
* @param key the key
* @return the mapped value, null if no match
*/
@Override
public V get(final Object key) {
purgeBeforeRead();
final Entry entry = getEntry(key);
if (entry == null) {
return null;
}
return entry.getValue();
}
/**
* Puts a key-value mapping into this map.
* Neither the key nor the value may be null.
*
* @param key the key to add, must not be null
* @param value the value to add, must not be null
* @return the value previously mapped to this key, null if none
* @throws NullPointerException if either the key or value is null
*/
@Override
public V put(final K key, final V value) {
if (key == null) {
throw new NullPointerException("null keys not allowed");
}
if (value == null) {
throw new NullPointerException("null values not allowed");
}
purgeBeforeWrite();
return super.put(key, value);
}
/**
* Removes the specified mapping from this map.
*
* @param key the mapping to remove
* @return the value mapped to the removed key, null if key not in map
*/
@Override
public V remove(final Object key) {
if (key == null) {
return null;
}
purgeBeforeWrite();
return super.remove(key);
}
/**
* Clears this map.
*/
@Override
public void clear() {
super.clear();
while (queue.poll() != null) {} // drain the queue
}
//-----------------------------------------------------------------------
/**
* Gets a MapIterator over the reference map.
* The iterator only returns valid key/value pairs.
*
* @return a map iterator
*/
@Override
public MapIterator mapIterator() {
return new ReferenceMapIterator(this);
}
/**
* Returns a set view of this map's entries.
* An iterator returned entry is valid until next() is called again.
* The setValue() method on the toArray entries has no effect.
*
* @return a set view of this map's entries
*/
@Override
public Set> entrySet() {
if (entrySet == null) {
entrySet = new ReferenceEntrySet(this);
}
return entrySet;
}
/**
* Returns a set view of this map's keys.
*
* @return a set view of this map's keys
*/
@Override
public Set keySet() {
if (keySet == null) {
keySet = new ReferenceKeySet(this);
}
return keySet;
}
/**
* Returns a collection view of this map's values.
*
* @return a set view of this map's values
*/
@Override
public Collection values() {
if (values == null) {
values = new ReferenceValues(this);
}
return values;
}
//-----------------------------------------------------------------------
/**
* Purges stale mappings from this map before read operations.
*
* This implementation calls {@link #purge()} to maintain a consistent state.
*/
protected void purgeBeforeRead() {
purge();
}
/**
* Purges stale mappings from this map before write operations.
*
* This implementation calls {@link #purge()} to maintain a consistent state.
*/
protected void purgeBeforeWrite() {
purge();
}
/**
* Purges stale mappings from this map.
*
* Note that this method is not synchronized! Special
* care must be taken if, for instance, you want stale
* mappings to be removed on a periodic basis by some
* background thread.
*/
protected void purge() {
Reference ref = queue.poll();
while (ref != null) {
purge(ref);
ref = queue.poll();
}
}
/**
* Purges the specified reference.
*
* @param ref the reference to purge
*/
protected void purge(final Reference ref) {
// The hashCode of the reference is the hashCode of the
// mapping key, even if the reference refers to the
// mapping value...
final int hash = ref.hashCode();
final int index = hashIndex(hash, data.length);
HashEntry previous = null;
HashEntry entry = data[index];
while (entry != null) {
if (((ReferenceEntry) entry).purge(ref)) {
if (previous == null) {
data[index] = entry.next;
} else {
previous.next = entry.next;
}
this.size--;
return;
}
previous = entry;
entry = entry.next;
}
}
//-----------------------------------------------------------------------
/**
* Gets the entry mapped to the key specified.
*
* @param key the key
* @return the entry, null if no match
*/
@Override
protected HashEntry getEntry(final Object key) {
if (key == null) {
return null;
}
return super.getEntry(key);
}
/**
* Gets the hash code for a MapEntry.
* Subclasses can override this, for example to use the identityHashCode.
*
* @param key the key to get a hash code for, may be null
* @param value the value to get a hash code for, may be null
* @return the hash code, as per the MapEntry specification
*/
protected int hashEntry(final Object key, final Object value) {
return (key == null ? 0 : key.hashCode()) ^
(value == null ? 0 : value.hashCode());
}
/**
* Compares two keys, in internal converted form, to see if they are equal.
*
* This implementation converts the key from the entry to a real reference
* before comparison.
*
* @param key1 the first key to compare passed in from outside
* @param key2 the second key extracted from the entry via entry.key
* @return true if equal
*/
@Override
@SuppressWarnings("unchecked")
protected boolean isEqualKey(final Object key1, Object key2) {
key2 = keyType == ReferenceStrength.HARD ? key2 : ((Reference) key2).get();
return key1 == key2 || key1.equals(key2);
}
/**
* Creates a ReferenceEntry instead of a HashEntry.
*
* @param next the next entry in sequence
* @param hashCode the hash code to use
* @param key the key to store
* @param value the value to store
* @return the newly created entry
*/
@Override
protected ReferenceEntry createEntry(final HashEntry next, final int hashCode,
final K key, final V value) {
return new ReferenceEntry(this, next, hashCode, key, value);
}
/**
* Creates an entry set iterator.
*
* @return the entrySet iterator
*/
@Override
protected Iterator> createEntrySetIterator() {
return new ReferenceEntrySetIterator(this);
}
/**
* Creates an key set iterator.
*
* @return the keySet iterator
*/
@Override
protected Iterator createKeySetIterator() {
return new ReferenceKeySetIterator(this);
}
/**
* Creates an values iterator.
*
* @return the values iterator
*/
@Override
protected Iterator createValuesIterator() {
return new ReferenceValuesIterator(this);
}
//-----------------------------------------------------------------------
/**
* EntrySet implementation.
*/
static class ReferenceEntrySet extends EntrySet {
protected ReferenceEntrySet(final AbstractHashedMap parent) {
super(parent);
}
@Override
public Object[] toArray() {
return toArray(new Object[size()]);
}
@Override
public T[] toArray(final T[] arr) {
// special implementation to handle disappearing entries
final ArrayList> list = new ArrayList>(size());
for (final Map.Entry entry : this) {
list.add(new DefaultMapEntry(entry));
}
return list.toArray(arr);
}
}
//-----------------------------------------------------------------------
/**
* KeySet implementation.
*/
static class ReferenceKeySet extends KeySet {
protected ReferenceKeySet(final AbstractHashedMap parent) {
super(parent);
}
@Override
public Object[] toArray() {
return toArray(new Object[size()]);
}
@Override
public T[] toArray(final T[] arr) {
// special implementation to handle disappearing keys
final List list = new ArrayList(size());
for (final K key : this) {
list.add(key);
}
return list.toArray(arr);
}
}
//-----------------------------------------------------------------------
/**
* Values implementation.
*/
static class ReferenceValues extends Values {
protected ReferenceValues(final AbstractHashedMap parent) {
super(parent);
}
@Override
public Object[] toArray() {
return toArray(new Object[size()]);
}
@Override
public T[] toArray(final T[] arr) {
// special implementation to handle disappearing values
final List list = new ArrayList(size());
for (final V value : this) {
list.add(value);
}
return list.toArray(arr);
}
}
//-----------------------------------------------------------------------
/**
* A MapEntry implementation for the map.
*
* If getKey() or getValue() returns null, it means
* the mapping is stale and should be removed.
*
* @since 3.1
*/
protected static class ReferenceEntry extends HashEntry {
/** The parent map */
private final AbstractReferenceMap parent;
/**
* Creates a new entry object for the ReferenceMap.
*
* @param parent the parent map
* @param next the next entry in the hash bucket
* @param hashCode the hash code of the key
* @param key the key
* @param value the value
*/
public ReferenceEntry(final AbstractReferenceMap parent, final HashEntry next,
final int hashCode, final K key, final V value) {
super(next, hashCode, null, null);
this.parent = parent;
this.key = toReference(parent.keyType, key, hashCode);
this.value = toReference(parent.valueType, value, hashCode); // the key hashCode is passed in deliberately
}
/**
* Gets the key from the entry.
* This method dereferences weak and soft keys and thus may return null.
*
* @return the key, which may be null if it was garbage collected
*/
@Override
@SuppressWarnings("unchecked")
public K getKey() {
return (K) (parent.keyType == ReferenceStrength.HARD ? key : ((Reference) key).get());
}
/**
* Gets the value from the entry.
* This method dereferences weak and soft value and thus may return null.
*
* @return the value, which may be null if it was garbage collected
*/
@Override
@SuppressWarnings("unchecked")
public V getValue() {
return (V) (parent.valueType == ReferenceStrength.HARD ? value : ((Reference) value).get());
}
/**
* Sets the value of the entry.
*
* @param obj the object to store
* @return the previous value
*/
@Override
@SuppressWarnings("unchecked")
public V setValue(final V obj) {
final V old = getValue();
if (parent.valueType != ReferenceStrength.HARD) {
((Reference) value).clear();
}
value = toReference(parent.valueType, obj, hashCode);
return old;
}
/**
* Compares this map entry to another.
*
* This implementation uses isEqualKey and
* isEqualValue on the main map for comparison.
*
* @param obj the other map entry to compare to
* @return true if equal, false if not
*/
@Override
public boolean equals(final Object obj) {
if (obj == this) {
return true;
}
if (obj instanceof Map.Entry == false) {
return false;
}
final Map.Entry entry = (Map.Entry)obj;
final Object entryKey = entry.getKey(); // convert to hard reference
final Object entryValue = entry.getValue(); // convert to hard reference
if (entryKey == null || entryValue == null) {
return false;
}
// compare using map methods, aiding identity subclass
// note that key is direct access and value is via method
return parent.isEqualKey(entryKey, key) &&
parent.isEqualValue(entryValue, getValue());
}
/**
* Gets the hashcode of the entry using temporary hard references.
*
* This implementation uses hashEntry on the main map.
*
* @return the hashcode of the entry
*/
@Override
public int hashCode() {
return parent.hashEntry(getKey(), getValue());
}
/**
* Constructs a reference of the given type to the given referent.
* The reference is registered with the queue for later purging.
*
* @param the type of the referenced object
* @param type HARD, SOFT or WEAK
* @param referent the object to refer to
* @param hash the hash code of the key of the mapping;
* this number might be different from referent.hashCode() if
* the referent represents a value and not a key
* @return the reference to the object
*/
protected Object toReference(final ReferenceStrength type, final T referent, final int hash) {
if (type == ReferenceStrength.HARD) {
return referent;
}
if (type == ReferenceStrength.SOFT) {
return new SoftRef(hash, referent, parent.queue);
}
if (type == ReferenceStrength.WEAK) {
return new WeakRef(hash, referent, parent.queue);
}
throw new Error();
}
/**
* Purges the specified reference
* @param ref the reference to purge
* @return true or false
*/
boolean purge(final Reference ref) {
boolean r = parent.keyType != ReferenceStrength.HARD && key == ref;
r = r || parent.valueType != ReferenceStrength.HARD && value == ref;
if (r) {
if (parent.keyType != ReferenceStrength.HARD) {
((Reference) key).clear();
}
if (parent.valueType != ReferenceStrength.HARD) {
((Reference) value).clear();
} else if (parent.purgeValues) {
value = null;
}
}
return r;
}
/**
* Gets the next entry in the bucket.
*
* @return the next entry in the bucket
*/
protected ReferenceEntry next() {
return (ReferenceEntry) next;
}
}
//-----------------------------------------------------------------------
/**
* Base iterator class.
*/
static class ReferenceBaseIterator {
/** The parent map */
final AbstractReferenceMap parent;
// These fields keep track of where we are in the table.
int index;
ReferenceEntry entry;
ReferenceEntry previous;
// These Object fields provide hard references to the
// current and next entry; this assures that if hasNext()
// returns true, next() will actually return a valid element.
K currentKey, nextKey;
V currentValue, nextValue;
int expectedModCount;
public ReferenceBaseIterator(final AbstractReferenceMap parent) {
super();
this.parent = parent;
index = parent.size() != 0 ? parent.data.length : 0;
// have to do this here! size() invocation above
// may have altered the modCount.
expectedModCount = parent.modCount;
}
public boolean hasNext() {
checkMod();
while (nextNull()) {
ReferenceEntry e = entry;
int i = index;
while (e == null && i > 0) {
i--;
e = (ReferenceEntry) parent.data[i];
}
entry = e;
index = i;
if (e == null) {
currentKey = null;
currentValue = null;
return false;
}
nextKey = e.getKey();
nextValue = e.getValue();
if (nextNull()) {
entry = entry.next();
}
}
return true;
}
private void checkMod() {
if (parent.modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
private boolean nextNull() {
return nextKey == null || nextValue == null;
}
protected ReferenceEntry nextEntry() {
checkMod();
if (nextNull() && !hasNext()) {
throw new NoSuchElementException();
}
previous = entry;
entry = entry.next();
currentKey = nextKey;
currentValue = nextValue;
nextKey = null;
nextValue = null;
return previous;
}
protected ReferenceEntry currentEntry() {
checkMod();
return previous;
}
public void remove() {
checkMod();
if (previous == null) {
throw new IllegalStateException();
}
parent.remove(currentKey);
previous = null;
currentKey = null;
currentValue = null;
expectedModCount = parent.modCount;
}
}
/**
* The EntrySet iterator.
*/
static class ReferenceEntrySetIterator
extends ReferenceBaseIterator implements Iterator> {
public ReferenceEntrySetIterator(final AbstractReferenceMap parent) {
super(parent);
}
public Map.Entry next() {
return nextEntry();
}
}
/**
* The keySet iterator.
*/
static class ReferenceKeySetIterator extends ReferenceBaseIterator implements Iterator {
@SuppressWarnings("unchecked")
ReferenceKeySetIterator(final AbstractReferenceMap parent) {
super((AbstractReferenceMap) parent);
}
public K next() {
return nextEntry().getKey();
}
}
/**
* The values iterator.
*/
static class ReferenceValuesIterator extends ReferenceBaseIterator implements Iterator {
@SuppressWarnings("unchecked")
ReferenceValuesIterator(final AbstractReferenceMap parent) {
super((AbstractReferenceMap) parent);
}
public V next() {
return nextEntry().getValue();
}
}
/**
* The MapIterator implementation.
*/
static class ReferenceMapIterator extends ReferenceBaseIterator implements MapIterator {
protected ReferenceMapIterator(final AbstractReferenceMap parent) {
super(parent);
}
public K next() {
return nextEntry().getKey();
}
public K getKey() {
final HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.GETKEY_INVALID);
}
return current.getKey();
}
public V getValue() {
final HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.GETVALUE_INVALID);
}
return current.getValue();
}
public V setValue(final V value) {
final HashEntry current = currentEntry();
if (current == null) {
throw new IllegalStateException(AbstractHashedMap.SETVALUE_INVALID);
}
return current.setValue(value);
}
}
//-----------------------------------------------------------------------
// These two classes store the hashCode of the key of
// of the mapping, so that after they're dequeued a quick
// lookup of the bucket in the table can occur.
/**
* A soft reference holder.
*/
static class SoftRef extends SoftReference {
/** the hashCode of the key (even if the reference points to a value) */
private final int hash;
public SoftRef(final int hash, final T r, final ReferenceQueue q) {
super(r, q);
this.hash = hash;
}
@Override
public int hashCode() {
return hash;
}
}
/**
* A weak reference holder.
*/
static class WeakRef extends WeakReference {
/** the hashCode of the key (even if the reference points to a value) */
private final int hash;
public WeakRef(final int hash, final T r, final ReferenceQueue q) {
super(r, q);
this.hash = hash;
}
@Override
public int hashCode() {
return hash;
}
}
//-----------------------------------------------------------------------
/**
* Replaces the superclass method to store the state of this class.
*
* Serialization is not one of the JDK's nicest topics. Normal serialization will
* initialise the superclass before the subclass. Sometimes however, this isn't
* what you want, as in this case the put() method on read can be
* affected by subclass state.
*
* The solution adopted here is to serialize the state data of this class in
* this protected method. This method must be called by the
* writeObject() of the first serializable subclass.
*
* Subclasses may override if they have a specific field that must be present
* on read before this implementation will work. Generally, the read determines
* what must be serialized here, if anything.
*
* @param out the output stream
* @throws IOException if an error occurs while writing to the stream
*/
@Override
protected void doWriteObject(final ObjectOutputStream out) throws IOException {
out.writeInt(keyType.value);
out.writeInt(valueType.value);
out.writeBoolean(purgeValues);
out.writeFloat(loadFactor);
out.writeInt(data.length);
for (final MapIterator it = mapIterator(); it.hasNext();) {
out.writeObject(it.next());
out.writeObject(it.getValue());
}
out.writeObject(null); // null terminate map
// do not call super.doWriteObject() as code there doesn't work for reference map
}
/**
* Replaces the superclass method to read the state of this class.
*
* Serialization is not one of the JDK's nicest topics. Normal serialization will
* initialise the superclass before the subclass. Sometimes however, this isn't
* what you want, as in this case the put() method on read can be
* affected by subclass state.
*
* The solution adopted here is to deserialize the state data of this class in
* this protected method. This method must be called by the
* readObject() of the first serializable subclass.
*
* Subclasses may override if the subclass has a specific field that must be present
* before put() or calculateThreshold() will work correctly.
*
* @param in the input stream
* @throws IOException if an error occurs while reading from the stream
* @throws ClassNotFoundException if an object read from the stream can not be loaded
*/
@Override
@SuppressWarnings("unchecked")
protected void doReadObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
this.keyType = ReferenceStrength.resolve(in.readInt());
this.valueType = ReferenceStrength.resolve(in.readInt());
this.purgeValues = in.readBoolean();
this.loadFactor = in.readFloat();
final int capacity = in.readInt();
init();
data = new HashEntry[capacity];
while (true) {
final K key = (K) in.readObject();
if (key == null) {
break;
}
final V value = (V) in.readObject();
put(key, value);
}
threshold = calculateThreshold(data.length, loadFactor);
// do not call super.doReadObject() as code there doesn't work for reference map
}
/**
* Provided protected read-only access to the key type.
* @param type the type to check against.
* @return true if keyType has the specified type
*/
protected boolean isKeyType(ReferenceStrength type) {
return this.keyType == type;
}
}
