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/*
* ====================================================================
* Project: openMDX/Core, http://www.openmdx.org/
* Description: Weak Registry
* Owner: OMEX AG, Switzerland, http://www.omex.ch
* ====================================================================
*
* This software is published under the BSD license as listed below.
*
* Copyright (c) 2010-2018, OMEX AG, Switzerland
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* * Neither the name of the openMDX team nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* ------------------
*
* This product includes software developed by other organizations as
* listed in the NOTICE file.
*/
package org.openmdx.base.collection;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* Weak Registry
*/
public class WeakRegistry implements Registry {
/**
* Constructor
*
* @param threadSafetyRequired tells whether concurrent access needs to be supported or not
*/
public WeakRegistry(
boolean threadSafetyRequired
) {
this.delegate = Maps.newMap(threadSafetyRequired);
this.queue = new ReferenceQueue<>();
}
/**
* The concurrent map holding the cache's references
*/
private Map> delegate;
/**
* The value reference queue
*/
private ReferenceQueue queue;
/**
* The value collection
*/
private final Set values = new AbstractSet() {
/* (non-Javadoc)
* @see java.util.AbstractCollection#iterator()
*/
@Override
public Iterator iterator(
) {
return new ValueIterator(
getDelegate().values().iterator()
);
}
/* (non-Javadoc)
* @see java.util.AbstractCollection#size()
*/
@Override
public int size() {
return getDelegate().size();
}
};
/**
* Retrieve the delegate after evicting its stale entries if required
*
* @return the thread-safe delegate
*/
protected Map> getDelegate(
){
assertOpen();
if(this.queue.poll() != null){
clearQueue();
evictStaleEntries();
}
return this.delegate;
}
/**
* Determines whether the registry is open or closed
*
* @return true if the reogistry is open
*/
private boolean isOpen(){
return this.delegate != null;
}
/**
* Assert that the registry is open
*
* @throws IllegalStateException if the registry is already closed
*/
private void assertOpen() {
if(this.delegate == null) {
throw new IllegalStateException("This registry is already closed");
}
}
/**
* Get rid of stale entries
*/
private synchronized void evictStaleEntries() {
for(
Iterator> i = this.delegate.values().iterator();
i.hasNext();
){
if(i.next().get() == null) {
i.remove();
}
}
}
/**
* Clear the reference queue
*/
private void clearQueue() {
while(this.queue.poll() != null) {
// Iterate as there is no clear() method
}
}
/**
* Clear the delegate
*/
private void clearDelegate() {
this.delegate.clear();
}
//------------------------------------------------------------------------
// Implements Registry
//------------------------------------------------------------------------
/* (non-Javadoc)
* @see org.openmdx.base.collection.Cache#clear()
*/
@Override
public void clear() {
assertOpen();
clearDelegate();
clearQueue();
}
/* (non-Javadoc)
* @see org.openmdx.base.collection.Registry#close()
*/
@Override
public synchronized void close() {
if(isOpen()) {
clearDelegate();
this.delegate = null;
clearQueue();
this.queue = null;
}
}
/* (non-Javadoc)
*
* @see org.openmdx.base.collection.Cache#get(java.lang.Object)
*/
@Override
public V get(K key) {
WeakReference v = getDelegate().get(key);
return v == null ? null : v.get();
}
/* (non-Javadoc)
* @see org.openmdx.base.collection.Cache#remove(java.lang.Object)
*/
@Override
public V remove(K key) {
WeakReference v = getDelegate().remove(key);
return v == null ? null : v.get();
}
/* (non-Javadoc)
* @see org.openmdx.base.collection.Cache#putIfAbsent(java.lang.Object, java.lang.Object)
*/
@Override
public V putUnlessPresent(K key, V value) {
WeakReference v = new WeakReference(value, this.queue);
Map> delegate = getDelegate();
WeakReference c = delegate.putIfAbsent(key, v);
if(c == null) {
return value;
} else {
V concurrent = c.get();
if(concurrent == null) {
delegate.put(key, v);
return value;
} else {
return concurrent;
}
}
}
/* (non-Javadoc)
* @see org.openmdx.base.collection.Cache#put(java.lang.Object, java.lang.Object)
*/
@Override
public V put(K key, V value) {
WeakReference v = new WeakReference(value, this.queue);
WeakReference c = getDelegate().put(key, v);
return c == null ? null : c.get();
}
/**
* Retrieve the objects managed by the cache
* *
* @return a collection with the objects managed by the cache
*
* @throws IllegalStateException if the registry is already closed
*/
@Override
public Set values(
){
assertOpen();
return this.values;
}
//------------------------------------------------------------------------
// Class ValueIterator
//------------------------------------------------------------------------
/**
* Value Iterator
*/
static class ValueIterator implements Iterator {
/**
* Constructor
*
* @param delegate
*/
public ValueIterator(
Iterator> delegate
){
this.delegate = delegate;
}
/**
* The reference iterator
*/
private final Iterator> delegate;
/**
* The prefetched value
*/
private V next = null;
/* (non-Javadoc)
* @see java.util.Iterator#hasNext()
*/
@Override
public boolean hasNext() {
while(this.next == null && this.delegate.hasNext()) {
this.next = this.delegate.next().get();
}
return this.next != null;
}
/* (non-Javadoc)
* @see java.util.Iterator#next()
*/
@Override
public V next() {
if(hasNext()) {
V next = this.next;
this.next = null;
return next;
} else {
throw new NoSuchElementException();
}
}
/* (non-Javadoc)
* @see java.util.Iterator#remove()
*/
@Override
public void remove() {
this.delegate.remove();
}
}
}
