com.yomahub.liteflow.util.CopyOnWriteHashMap Maven / Gradle / Ivy
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright (c) 2010-2013 Oracle and/or its affiliates. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common Development
* and Distribution License("CDDL") (collectively, the "License"). You
* may not use this file except in compliance with the License. You can
* obtain a copy of the License at
* http://glassfish.java.net/public/CDDL+GPL_1_1.html
* or packager/legal/LICENSE.txt. See the License for the specific
* language governing permissions and limitations under the License.
*
* When distributing the software, include this License Header Notice in each
* file and include the License file at packager/legal/LICENSE.txt.
*
* GPL Classpath Exception:
* Oracle designates this particular file as subject to the "Classpath"
* exception as provided by Oracle in the GPL Version 2 section of the License
* file that accompanied this code.
*
* Modifications:
* If applicable, add the following below the License Header, with the fields
* enclosed by brackets [] replaced by your own identifying information:
* "Portions Copyright [year] [name of copyright owner]"
*
* Contributor(s):
* If you wish your version of this file to be governed by only the CDDL or
* only the GPL Version 2, indicate your decision by adding "[Contributor]
* elects to include this software in this distribution under the [CDDL or GPL
* Version 2] license." If you don't indicate a single choice of license, a
* recipient has the option to distribute your version of this file under
* either the CDDL, the GPL Version 2 or to extend the choice of license to
* its licensees as provided above. However, if you add GPL Version 2 code
* and therefore, elected the GPL Version 2 license, then the option applies
* only if the new code is made subject to such option by the copyright
* holder.
*/
package com.yomahub.liteflow.util;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* A basic copy on write HashMap.
*
* If an instance is cloned then any methods invoked on the instance or clone that result
* in state modification will result in copying of the state before modification.
*
* @author [email protected]
* @author [email protected]
* @author Bryan.Zhang
*/
public class CopyOnWriteHashMap extends ConcurrentHashMap {
volatile ConcurrentHashMap view;
private ConcurrentHashMap duplicate(ConcurrentHashMap original) {
// SUBTLETY: note that original.entrySet() grabs the entire contents of the
// original Map in a
// single call. This means that if the original map is Thread-safe or another
// CopyOnWriteHashMap,
// we can safely iterate over the list of entries.
return new ConcurrentHashMap<>(original);
}
public CopyOnWriteHashMap(ConcurrentHashMap that) {
this.view = duplicate(that);
}
public CopyOnWriteHashMap() {
this(new ConcurrentHashMap<>());
}
@Override
public CopyOnWriteHashMap clone() {
return new CopyOnWriteHashMap(view);
}
/*
* ********************** READ-ONLY OPERATIONS
**********************/
@Override
public int size() {
return view.size();
}
@Override
public boolean isEmpty() {
return view.isEmpty();
}
@Override
public boolean containsKey(Object key) {
return view.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return view.containsValue(value);
}
@Override
public V get(Object key) {
return view.get(key);
}
@Override
public KeySetView keySet() {
return view.keySet();
}
@Override
public Collection values() {
return view.values();
}
@Override
public Set> entrySet() {
return view.entrySet();
}
@Override
public String toString() {
return view.toString();
}
/*
* ********************** UPDATING OPERATIONS
*
* These operations all follow a common pattern:
*
* 1. Create a copy of the existing view. 2. Update the copy. 3. Perform a volatile
* write to replace the existing view.
*
* Note that if you are not concerned about lost updates, you could dispense with the
* synchronization entirely.
**********************/
@Override
public V put(K key, V value) {
synchronized (this) {
ConcurrentHashMap newCore = duplicate(view);
V result = newCore.put(key, value);
view = newCore; // volatile write
return result;
}
}
@Override
public V remove(Object key) {
synchronized (this) {
ConcurrentHashMap newCore = duplicate(view);
V result = newCore.remove(key);
view = newCore; // volatile write
return result;
}
}
@Override
public void putAll(Map t) {
synchronized (this) {
ConcurrentHashMap newCore = duplicate(view);
newCore.putAll(t);
view = newCore; // volatile write
}
}
@Override
public void clear() {
synchronized (this) {
view = new ConcurrentHashMap<>(); // volatile write
}
}
}