/*
* Copyright (C) 2011 The Guava Authors
*
* 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.util.concurrent;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Function;
import com.google.common.collect.Maps;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;
/**
* A map containing {@code long} values that can be atomically updated. While writes to a
* traditional {@code Map} rely on {@code put(K, V)}, the typical mechanism for writing to this map
* is {@code addAndGet(K, long)}, which adds a {@code long} to the value currently associated with
* {@code K}. If a key has not yet been associated with a value, its implicit value is zero.
*
* <p>Most methods in this class treat absent values and zero values identically, as individually
* documented. Exceptions to this are {@link #containsKey}, {@link #size}, {@link #isEmpty},
* {@link #asMap}, and {@link #toString}.
*
* <p>Instances of this class may be used by multiple threads concurrently. All operations are
* atomic unless otherwise noted.
*
* <p><b>Note:</b> If your values are always positive and less than 2^31, you may wish to use a
* {@link com.google.common.collect.Multiset} such as
* {@link com.google.common.collect.ConcurrentHashMultiset} instead.
*
* <b>Warning:</b> Unlike {@code Multiset}, entries whose values are zero are not automatically
* removed from the map. Instead they must be removed manually with {@link #removeAllZeros}.
*
* @author Charles Fry
* @since 11.0
*/
@GwtCompatible
public final class AtomicLongMap<K> {
private final ConcurrentHashMap<K, AtomicLong> map;
private AtomicLongMap(ConcurrentHashMap<K, AtomicLong> map) {
this.map = checkNotNull(map);
}
/**
* Creates an {@code AtomicLongMap}.
*/
public static <K> AtomicLongMap<K> create() {
return new AtomicLongMap<K>(new ConcurrentHashMap<K, AtomicLong>());
}
/**
* Creates an {@code AtomicLongMap} with the same mappings as the specified {@code Map}.
*/
public static <K> AtomicLongMap<K> create(Map<? extends K, ? extends Long> m) {
AtomicLongMap<K> result = create();
result.putAll(m);
return result;
}
/**
* Returns the value associated with {@code key}, or zero if there is no value associated with
* {@code key}.
*/
public long get(K key) {
AtomicLong atomic = map.get(key);
return atomic == null ? 0L : atomic.get();
}
/**
* Increments by one the value currently associated with {@code key}, and returns the new value.
*/
public long incrementAndGet(K key) {
return addAndGet(key, 1);
}
/**
* Decrements by one the value currently associated with {@code key}, and returns the new value.
*/
public long decrementAndGet(K key) {
return addAndGet(key, -1);
}
/**
* Adds {@code delta} to the value currently associated with {@code key}, and returns the new
* value.
*/
public long addAndGet(K key, long delta) {
outer: for (;;) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
atomic = map.putIfAbsent(key, new AtomicLong(delta));
if (atomic == null) {
return delta;
}
// atomic is now non-null; fall through
}
for (;;) {
long oldValue = atomic.get();
if (oldValue == 0L) {
// don't compareAndSet a zero
if (map.replace(key, atomic, new AtomicLong(delta))) {
return delta;
}
// atomic replaced
continue outer;
}
long newValue = oldValue + delta;
if (atomic.compareAndSet(oldValue, newValue)) {
return newValue;
}
// value changed
}
}
}
/**
* Increments by one the value currently associated with {@code key}, and returns the old value.
*/
public long getAndIncrement(K key) {
return getAndAdd(key, 1);
}
/**
* Decrements by one the value currently associated with {@code key}, and returns the old value.
*/
public long getAndDecrement(K key) {
return getAndAdd(key, -1);
}
/**
* Adds {@code delta} to the value currently associated with {@code key}, and returns the old
* value.
*/
public long getAndAdd(K key, long delta) {
outer: for (;;) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
atomic = map.putIfAbsent(key, new AtomicLong(delta));
if (atomic == null) {
return 0L;
}
// atomic is now non-null; fall through
}
for (;;) {
long oldValue = atomic.get();
if (oldValue == 0L) {
// don't compareAndSet a zero
if (map.replace(key, atomic, new AtomicLong(delta))) {
return 0L;
}
// atomic replaced
continue outer;
}
long newValue = oldValue + delta;
if (atomic.compareAndSet(oldValue, newValue)) {
return oldValue;
}
// value changed
}
}
}
/**
* Associates {@code newValue} with {@code key} in this map, and returns the value previously
* associated with {@code key}, or zero if there was no such value.
*/
public long put(K key, long newValue) {
outer: for (;;) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
atomic = map.putIfAbsent(key, new AtomicLong(newValue));
if (atomic == null) {
return 0L;
}
// atomic is now non-null; fall through
}
for (;;) {
long oldValue = atomic.get();
if (oldValue == 0L) {
// don't compareAndSet a zero
if (map.replace(key, atomic, new AtomicLong(newValue))) {
return 0L;
}
// atomic replaced
continue outer;
}
if (atomic.compareAndSet(oldValue, newValue)) {
return oldValue;
}
// value changed
}
}
}
/**
* Copies all of the mappings from the specified map to this map. The effect of this call is
* equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
* {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
* if the specified map is modified while the operation is in progress.
*/
public void putAll(Map<? extends K, ? extends Long> m) {
for (Map.Entry<? extends K, ? extends Long> entry : m.entrySet()) {
put(entry.getKey(), entry.getValue());
}
}
/**
* Removes and returns the value associated with {@code key}. If {@code key} is not
* in the map, this method has no effect and returns zero.
*/
public long remove(K key) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
return 0L;
}
for (;;) {
long oldValue = atomic.get();
if (oldValue == 0L || atomic.compareAndSet(oldValue, 0L)) {
// only remove after setting to zero, to avoid concurrent updates
map.remove(key, atomic);
// succeed even if the remove fails, since the value was already adjusted
return oldValue;
}
}
}
/**
* Removes all mappings from this map whose values are zero.
*
* <p>This method is not atomic: the map may be visible in intermediate states, where some
* of the zero values have been removed and others have not.
*/
public void removeAllZeros() {
for (K key : map.keySet()) {
AtomicLong atomic = map.get(key);
if (atomic != null && atomic.get() == 0L) {
map.remove(key, atomic);
}
}
}
/**
* Returns the sum of all values in this map.
*
* <p>This method is not atomic: the sum may or may not include other concurrent operations.
*/
public long sum() {
long sum = 0L;
for (AtomicLong value : map.values()) {
sum = sum + value.get();
}
return sum;
}
private transient Map<K, Long> asMap;
/**
* Returns a live, read-only view of the map backing this {@code AtomicLongMap}.
*/
public Map<K, Long> asMap() {
Map<K, Long> result = asMap;
return (result == null) ? asMap = createAsMap() : result;
}
private Map<K, Long> createAsMap() {
return Collections.unmodifiableMap(
Maps.transformValues(map, new Function<AtomicLong, Long>() {
@Override
public Long apply(AtomicLong atomic) {
return atomic.get();
}
}));
}
/**
* Returns true if this map contains a mapping for the specified key.
*/
public boolean containsKey(Object key) {
return map.containsKey(key);
}
/**
* Returns the number of key-value mappings in this map. If the map contains more than
* {@code Integer.MAX_VALUE} elements, returns {@code Integer.MAX_VALUE}.
*/
public int size() {
return map.size();
}
/**
* Returns {@code true} if this map contains no key-value mappings.
*/
public boolean isEmpty() {
return map.isEmpty();
}
/**
* Removes all of the mappings from this map. The map will be empty after this call returns.
*
* <p>This method is not atomic: the map may not be empty after returning if there were concurrent
* writes.
*/
public void clear() {
map.clear();
}
@Override
public String toString() {
return map.toString();
}
/*
* ConcurrentMap operations which we may eventually add.
*
* The problem with these is that remove(K, long) has to be done in two phases by definition ---
* first decrementing to zero, and then removing. putIfAbsent or replace could observe the
* intermediate zero-state. Ways we could deal with this are:
*
* - Don't define any of the ConcurrentMap operations. This is the current state of affairs.
*
* - Define putIfAbsent and replace as treating zero and absent identically (as currently
* implemented below). This is a bit surprising with putIfAbsent, which really becomes
* putIfZero.
*
* - Allow putIfAbsent and replace to distinguish between zero and absent, but don't implement
* remove(K, long). Without any two-phase operations it becomes feasible for all remaining
* operations to distinguish between zero and absent. If we do this, then perhaps we should add
* replace(key, long).
*
* - Introduce a special-value private static final AtomicLong that would have the meaning of
* removal-in-progress, and rework all operations to properly distinguish between zero and
* absent.
*/
/**
* If {@code key} is not already associated with a value or if {@code key} is associated with
* zero, associate it with {@code newValue}. Returns the previous value associated with
* {@code key}, or zero if there was no mapping for {@code key}.
*/
long putIfAbsent(K key, long newValue) {
for (;;) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
atomic = map.putIfAbsent(key, new AtomicLong(newValue));
if (atomic == null) {
return 0L;
}
// atomic is now non-null; fall through
}
long oldValue = atomic.get();
if (oldValue == 0L) {
// don't compareAndSet a zero
if (map.replace(key, atomic, new AtomicLong(newValue))) {
return 0L;
}
// atomic replaced
continue;
}
return oldValue;
}
}
/**
* If {@code (key, expectedOldValue)} is currently in the map, this method replaces
* {@code expectedOldValue} with {@code newValue} and returns true; otherwise, this method
* returns false.
*
* <p>If {@code expectedOldValue} is zero, this method will succeed if {@code (key, zero)}
* is currently in the map, or if {@code key} is not in the map at all.
*/
boolean replace(K key, long expectedOldValue, long newValue) {
if (expectedOldValue == 0L) {
return putIfAbsent(key, newValue) == 0L;
} else {
AtomicLong atomic = map.get(key);
return (atomic == null) ? false : atomic.compareAndSet(expectedOldValue, newValue);
}
}
/**
* If {@code (key, value)} is currently in the map, this method removes it and returns
* true; otherwise, this method returns false.
*/
boolean remove(K key, long value) {
AtomicLong atomic = map.get(key);
if (atomic == null) {
return false;
}
long oldValue = atomic.get();
if (oldValue != value) {
return false;
}
if (oldValue == 0L || atomic.compareAndSet(oldValue, 0L)) {
// only remove after setting to zero, to avoid concurrent updates
map.remove(key, atomic);
// succeed even if the remove fails, since the value was already adjusted
return true;
}
// value changed
return false;
}
}