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/*
* Copyright 2008-present MongoDB, Inc.
* Copyright (c) 2008-2014 Atlassian Pty Ltd
*
* 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 org.bson.util;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* A thread-safe variant of {@link java.util.Map} in which all mutative operations (the "destructive" operations described by {@link
* java.util.Map} put, remove and so on) are implemented by making a fresh copy of the underlying map.
*
* This is ordinarily too costly, but may be more efficient than alternatives when traversal operations vastly out-number
* mutations, and is useful when you cannot or don't want to synchronize traversals, yet need to preclude interference among concurrent
* threads. The "snapshot" style iterators on the collections returned by {@link #entrySet()}, {@link #keySet()} and {@link #values()} use a
* reference to the internal map at the point that the iterator was created. This map never changes during the lifetime of the iterator, so
* interference is impossible and the iterator is guaranteed not to throw {@code ConcurrentModificationException}. The iterators will not
* reflect additions, removals, or changes to the list since the iterator was created. Removing elements via these iterators is not
* supported. The mutable operations on these collections (remove, retain etc.) are supported but as with the {@link java.util.Map}
* interface, add and addAll are not and throw {@link UnsupportedOperationException}.
The actual copy is performed by an abstract
* {@link #copy(java.util.Map)} method. The method is responsible for the underlying Map implementation (for instance a {@link
* java.util.HashMap}, {@link java.util.TreeMap}, {@link java.util.LinkedHashMap} etc.) and therefore the semantics of what this map will
* cope with as far as null keys and values, iteration ordering etc. See the note below about suitable candidates for underlying Map
* implementations
*
* There are supplied implementations for the common j.u.c {@link java.util.Map} implementations via the {@link CopyOnWriteMap} static
* {@link Builder}.
*
* Collection views of the keys, values and entries are optionally {@link View.Type#LIVE live} or {@link View.Type#STABLE stable}. Live
* views are modifiable will cause a copy if a modifying method is called on them. Methods on these will reflect the current state of the
* collection, although iterators will be snapshot style. If the collection views are stable they are unmodifiable, and will be a snapshot
* of the state of the map at the time the collection was asked for.
*
* Please note that the thread-safety guarantees are limited to the thread-safety of the non-mutative (non-destructive)
* operations of the underlying map implementation. For instance some implementations such as {@link java.util.WeakHashMap} and {@link
* java.util.LinkedHashMap} with access ordering are actually structurally modified by the {@link #get(Object)} method and are therefore not
* suitable candidates as delegates for this class.
*
* @param the key type
* @param the value type
* @author Jed Wesley-Smith
*/
abstract class CopyOnWriteMap extends AbstractCopyOnWriteMap> {
private static final long serialVersionUID = 7935514534647505917L;
/**
* Get a {@link Builder} for a CopyOnWriteMap instance.
*
* @param key type
* @param value type
* @return a fresh builder
*/
public static Builder builder() {
return new Builder();
}
/**
* Build a {@link CopyOnWriteMap} and specify all the options.
*
* @param key type
* @param value type
*/
public static class Builder {
private View.Type viewType = View.Type.STABLE;
private final Map initialValues = new HashMap();
Builder() {
}
/**
* Views are stable (fixed in time) and unmodifiable.
*/
public Builder stableViews() {
viewType = View.Type.STABLE;
return this;
}
/**
* Views are live (reflecting concurrent updates) and mutator methods are supported.
*/
public Builder addAll(final Map values) {
initialValues.putAll(values);
return this;
}
/**
* Views are live (reflecting concurrent updates) and mutator methods are supported.
*/
public Builder liveViews() {
viewType = View.Type.LIVE;
return this;
}
public CopyOnWriteMap newHashMap() {
return new Hash(initialValues, viewType);
}
public CopyOnWriteMap newLinkedMap() {
return new Linked(initialValues, viewType);
}
}
/**
* Creates a new {@link CopyOnWriteMap} with an underlying {@link HashMap}.
*
* This map has {@link View.Type#STABLE stable} views.
*/
public static CopyOnWriteMap newHashMap() {
Builder builder = builder();
return builder.newHashMap();
}
/**
* Creates a new {@link CopyOnWriteMap} with an underlying {@link HashMap} using the supplied map as the initial values.
*
* This map has {@link View.Type#STABLE stable} views.
*/
public static CopyOnWriteMap newHashMap(final Map map) {
Builder builder = builder();
return builder.addAll(map).newHashMap();
}
/**
* Creates a new {@link CopyOnWriteMap} with an underlying {@link java.util.LinkedHashMap}. Iterators for this map will be return
* elements in insertion order.
*
* This map has {@link View.Type#STABLE stable} views.
*/
public static CopyOnWriteMap newLinkedMap() {
Builder builder = builder();
return builder.newLinkedMap();
}
/**
* Creates a new {@link CopyOnWriteMap} with an underlying {@link java.util.LinkedHashMap} using the supplied map as the initial
* values. Iterators for this map will be return elements in insertion order.
*
* This map has {@link View.Type#STABLE stable} views.
*/
public static CopyOnWriteMap newLinkedMap(final Map map) {
Builder builder = builder();
return builder.addAll(map).newLinkedMap();
}
//
// constructors
//
/**
* Create a new {@link CopyOnWriteMap} with the supplied {@link Map} to initialize the values.
*
* @param map the initial map to initialize with
*/
protected CopyOnWriteMap(final Map map) {
this(map, View.Type.LIVE);
}
/**
* Create a new empty {@link CopyOnWriteMap}.
*/
protected CopyOnWriteMap() {
this(Collections.emptyMap(), View.Type.LIVE);
}
/**
* Create a new {@link CopyOnWriteMap} with the supplied {@link Map} to initialize the values. This map may be optionally modified using
* any of the key, entry or value views
*
* @param map the initial map to initialize with
*/
protected CopyOnWriteMap(final Map map, final View.Type viewType) {
super(map, viewType);
}
/**
* Create a new empty {@link CopyOnWriteMap}. This map may be optionally modified using any of the key, entry or value views
*/
protected CopyOnWriteMap(final View.Type viewType) {
super(Collections.emptyMap(), viewType);
}
@Override
// @GuardedBy("internal-lock")
protected abstract > Map copy(N map);
//
// inner classes
//
/**
* Uses {@link HashMap} instances as its internal storage.
*/
static class Hash extends CopyOnWriteMap {
private static final long serialVersionUID = 5221824943734164497L;
Hash(final Map map, final View.Type viewType) {
super(map, viewType);
}
@Override
public > Map copy(final N map) {
return new HashMap(map);
}
}
/**
* Uses {@link java.util.LinkedHashMap} instances as its internal storage.
*/
static class Linked extends CopyOnWriteMap {
private static final long serialVersionUID = -8659999465009072124L;
Linked(final Map map, final View.Type viewType) {
super(map, viewType);
}
@Override
public > Map copy(final N map) {
return new LinkedHashMap(map);
}
}
}