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/*
* Copyright (C) 2007 Google Inc.
*
* Licensed 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 com.google.common.collect;
import com.google.common.base.Nullable;
import static com.google.common.base.Preconditions.checkArgument;
import java.io.Serializable;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* A multiset that supports concurrent modifications and that provides atomic
* versions of most {@code Multiset} operations (exceptions where noted).
*
* This implementation is backed by a {@link ConcurrentMap}, and several of
* its properties will depend on the behavior of this backing map: for example,
* it can contain only values that are legal keys for the backing map. Thus,
* when using the default {@link ConcurrentHashMap}, this implementation cannot
* contain {@code null}.
*
* @author Cliff L. Biffle
*/
public final class ConcurrentMultiset extends AbstractMultiset
implements Serializable {
/*
* The ConcurrentMultiset's atomic operations are implemented in terms of
* ConcurrentMap's atomic operations. Many of them, such as add(E, int), are
* read-modify-write sequences, and so are implemented as loops that wrap
* ConcurrentMap's compare-and-set operations (like putIfAbsent).
*/
/** The number of occurrences of each element. */
private final ConcurrentMap countMap;
/**
* Creates an empty instance using a {@link ConcurrentHashMap} to store
* elements and their counts.
*
* The {@code ConcurrentHashMap} will have default capacity, load factor,
* and concurrency settings. For more control, use
* {@link #ConcurrentMultiset(ConcurrentMap)}.
*/
public ConcurrentMultiset() {
this(new ConcurrentHashMap());
}
/**
* Creates an instance using a {@link ConcurrentHashMap} to store elements
* and their counts, and initially containing all the elements from a given
* collection.
*
* The {@code ConcurrentHashMap} will have default capacity, load factor,
* and concurrency settings. For more control, use
* {@link #ConcurrentMultiset(ConcurrentMap)}.
*/
public ConcurrentMultiset(Collection collection) {
this(new ConcurrentHashMap());
addAll(collection);
}
/**
* Creates an instance using {@code countMap} to store elements and their
* counts.
*
* This instance will assume ownership of {@code countMap}, and other code
* should not maintain references to the map or modify it in any way.
*
* @param countMap backing map for storing the elements in the multiset and
* their counts. Must be empty.
* @throws IllegalArgumentException if {@code countMap} is not empty
*/
public ConcurrentMultiset(ConcurrentMap countMap) {
checkArgument(countMap.isEmpty());
this.countMap = countMap;
}
// Query Operations
/**
* Returns the number of occurrences of {@code element} in this multiset.
*
* @param element the element to look for
* @return the nonnegative number of occurrences of the element
*/
@Override public int count(@Nullable Object element) {
return unbox(countMap.get(element));
}
/*
* Note: the superclass toArray() methods assume that size() gives a correct
* answer, which ours does not.
*/
@Override public Object[] toArray() {
return snapshot().toArray();
}
@Override public T[] toArray(T[] array) {
return snapshot().toArray(array);
}
/*
* We'd love to use 'new ArrayList(this)' or 'list.addAll(this)', but
* either of these would recurse back to us again!
*/
private List snapshot() {
List list = Lists.newArrayListWithExpectedSize(size());
for (Multiset.Entry entry : entrySet()) {
E element = entry.getElement();
for (int i = entry.getCount(); i > 0; i--) {
list.add(element);
}
}
return list;
}
// Modification Operations
/**
* Adds a number of occurrences of the specified element to this multiset.
*
* To succeed, {@code element} must be a legal key in the backing map. In
* the case of the default {@link ConcurrentHashMap}, this means it must not
* be {@code null}, but other {@code Map} implementations may allow {@code
* null}.
*
* @param element the element to add
* @param occurrences the number of occurrences to add
* @return {@code true} if the collection changed as a result (this should
* always be the case unless {@code occurrences} is zero)
* @throws IllegalArgumentException if {@code occurrences} is negative, or if
* the resulting amount would exceed {@link Integer#MAX_VALUE}
*/
@Override public boolean add(E element, int occurrences) {
if (occurrences == 0) {
return false;
}
checkArgument(occurrences > 0, "Invalid occurrences: %s", occurrences);
while (true) {
int current = count(element);
if (current == 0) {
if (countMap.putIfAbsent(element, occurrences) == null) {
return true;
}
} else {
checkArgument(occurrences <= Integer.MAX_VALUE - current,
"Overflow adding %s occurrences to a count of %s",
occurrences, current);
int next = current + occurrences;
if (countMap.replace(element, current, next)) {
return true;
}
}
// If we're still here, there was a race, so just try again.
}
}
/**
* Removes a number of occurrences of the specified element from this
* multiset. If the multiset contains fewer than this number of occurrences to
* begin with, all occurrences will be removed.
*
* @param element the element whose occurrences should be removed
* @param occurrences the number of occurrences of this element to remove
* @return the number of occurrences that were successfully removed (zero if
* the element was not present)
* @throws IllegalArgumentException if {@code occurrences} is negative
*/
@Override public int remove(@Nullable Object element, int occurrences) {
if (occurrences == 0) {
return 0;
}
checkArgument(occurrences > 0, "Invalid occurrences: %s", occurrences);
while (true) {
int current = count(element);
if (current == 0) {
return 0;
}
if (occurrences >= current) {
if (countMap.remove(element, current)) {
return current;
}
} else {
// We know it's an "E" because it already exists in the map.
@SuppressWarnings("unchecked")
E casted = (E) element;
if (countMap.replace(casted, current, current - occurrences)) {
return occurrences;
}
}
// If we're still here, there was a race, so just try again.
}
}
/**
* Removes all occurrences of the specified element from this multiset.
* This method complements {@link Multiset#remove(Object)}, which removes only
* one occurrence at a time.
*
* @param element the element whose occurrences should all be removed
* @return the number of occurrences successfully removed, possibly zero
*/
@Override public int removeAllOccurrences(@Nullable Object element) {
return unbox(countMap.remove(element));
}
// TODO: move this above isEmpty() where it belongs
/**
* {@inheritDoc}
*
*
If the data in the multiset is modified by any other threads during this
* method, it is undefined which (if any) of these modifications will be
* reflected in the result.
*/
@Override public int size() {
long sum = 0L;
for (Integer value : countMap.values()) {
sum += value;
}
return (int) Math.min(sum, Integer.MAX_VALUE);
}
/**
* Adds or removes occurrences of {@code element} such that the {@link #count}
* of the element becomes {@code count}.
*
* @return the count of {@code element} in the multiset before this call
* @throws IllegalArgumentException if {@code count} is negative
*/
public int setCount(E element, int count) {
checkArgument(count >= 0, "Invalid count: %s", count);
return (count == 0)
? removeAllOccurrences(element)
: unbox(countMap.put(element, count));
}
/**
* Sets the number of occurrences of {@code element} to {@code newCount}, but
* only if the count is currently {@code oldCount}. If {@code element} does
* not appear in the multiset exactly {@code oldCount} times, no changes will
* be made.
*
* @return {@code true} if the change was successful. This usually indicates
* that the multiset has been modified, but not always: in the case
* that {@code oldCount == newCount}, the method will return
* {@code true} if the condition was met.
* @throws IllegalArgumentException if {@code oldCount} or {@code newCount} is
* negative
*/
public boolean setCount(E element, int oldCount, int newCount) {
checkArgument(oldCount >= 0, "Invalid oldCount: %s", oldCount);
checkArgument(newCount >= 0, "Invalid newCount: %s", newCount);
if (newCount == 0) {
if (oldCount == 0) {
// No change to make, but must return true if the element is not present
return !countMap.containsKey(element);
} else {
return countMap.remove(element, box(oldCount));
}
}
if (oldCount == 0) {
return countMap.putIfAbsent(element, newCount) == null;
}
return countMap.replace(element, oldCount, newCount);
}
// TODO: move this above removeAllOccurrences() where it belongs
/**
* Removes exactly the specified number of occurrences of {@code element}, or
* makes no change if this is not possible.
*
*
This method, in contrast to {@link #remove(Object, int)}, has no effect
* when the element count is smaller than {@code occurrences}.
*
* @param element the element to remove
* @param occurrences the number of occurrences of {@code element} to remove
* @return {@code true} if the removal was possible (including if {@code
* occurrences} is zero)
*/
public boolean removeExactly(@Nullable Object element, int occurrences) {
if (occurrences == 0) {
return true;
}
checkArgument(occurrences > 0, "Invalid occurrences: %s", occurrences);
while (true) {
int current = count(element);
if (occurrences > current) {
return false;
}
if (occurrences == current) {
if (countMap.remove(element, occurrences)) {
return true;
}
} else {
@SuppressWarnings("unchecked") // it's in the map, must be an "E"
E casted = (E) element;
if (countMap.replace(casted, current, current - occurrences)) {
return true;
}
}
// If we're still here, there was a race, so just try again.
}
}
// Views
@Override public Set elementSet() {
return countMap.keySet();
}
private transient EntrySet entrySet;
@Override public Set> entrySet() {
EntrySet es = entrySet;
return (es == null) ? (entrySet = new EntrySet()) : es;
}
private class EntrySet extends AbstractSet> {
@Override public int size() {
return countMap.size();
}
@Override public boolean isEmpty() {
return countMap.isEmpty();
}
@Override public boolean contains(Object object) {
if (object instanceof Multiset.Entry) {
Multiset.Entry entry = (Multiset.Entry) object;
Object element = entry.getElement();
int entryCount = entry.getCount();
return entryCount > 0 && count(element) == entryCount;
}
return false;
}
@Override public Iterator> iterator() {
final Iterator> backingIterator
= countMap.entrySet().iterator();
return new Iterator>() {
public boolean hasNext() {
return backingIterator.hasNext();
}
public Multiset.Entry next() {
Map.Entry backingEntry = backingIterator.next();
return Multisets.immutableEntry(
backingEntry.getKey(), backingEntry.getValue());
}
public void remove() {
backingIterator.remove();
}
};
}
/*
* Note: the superclass toArray() methods assume that size() gives a correct
* answer, which ours does not.
*/
@Override public Object[] toArray() {
return snapshot().toArray();
}
@Override public T[] toArray(T[] array) {
return snapshot().toArray(array);
}
/*
* We'd love to use 'new ArrayList(this)' or 'list.addAll(this)', but
* either of these would recurse back to us again!
*/
private List> snapshot() {
List> list = Lists.newArrayListWithExpectedSize(size());
for (Multiset.Entry entry : this) {
list.add(entry);
}
return list;
}
@Override public boolean remove(Object object) {
if (object instanceof Multiset.Entry) {
Multiset.Entry entry = (Multiset.Entry) object;
Object element = entry.getElement();
return countMap.remove(element, box(entry.getCount()));
}
return false;
}
@Override public void clear() {
countMap.clear();
}
}
/*
* We use a special form of boxing and unboxing that treats null as zero
* and zero as null.
*/
private static Integer box(int i) {
return (i == 0) ? null : i;
}
private static int unbox(Integer i) {
return (i == null) ? 0 : i;
}
private static final long serialVersionUID = 0L;
}