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package com.sun.jersey.client.impl;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
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]
*/
public class CopyOnWriteHashMap implements Map {
private volatile Map core;
volatile Map view;
private final AtomicBoolean requiresCopyOnWrite;
public CopyOnWriteHashMap() {
this.core = new HashMap();
this.requiresCopyOnWrite = new AtomicBoolean(false);
}
private CopyOnWriteHashMap(CopyOnWriteHashMap that) {
this.core = that.core;
this.requiresCopyOnWrite = new AtomicBoolean(true);
}
@Override
public CopyOnWriteHashMap clone() {
try {
return new CopyOnWriteHashMap(this);
} finally {
requiresCopyOnWrite.set(true);
}
}
private void copy() {
if (requiresCopyOnWrite.compareAndSet(true, false)) {
core = new HashMap(core);
view = null;
}
}
@Override
public int size() {
return core.size();
}
@Override
public boolean isEmpty() {
return core.isEmpty();
}
@Override
public boolean containsKey(Object key) {
return core.containsKey(key);
}
@Override
public boolean containsValue(Object value) {
return core.containsValue(value);
}
@Override
public V get(Object key) {
return core.get(key);
}
@Override
public V put(K key, V value) {
copy();
return core.put(key, value);
}
@Override
public V remove(Object key) {
copy();
return core.remove(key);
}
@Override
public void putAll(Map t) {
copy();
core.putAll(t);
}
@Override
public void clear() {
core = new HashMap();
view = null;
copy();
}
@Override
public Set keySet() {
return getView().keySet();
}
@Override
public Collection values() {
return getView().values();
}
@Override
public Set> entrySet() {
return getView().entrySet();
}
@Override
public String toString() {
return core.toString();
}
private Map getView() {
Map result = view; // volatile read
if (result == null) {
result = Collections.unmodifiableMap(core);
view = result; // volatile write
}
return result;
}
}