/*
* The contents of this file are subject to the Mozilla Public License Version 1.1
* (the "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at .
*
* Software distributed under the License is distributed on an "AS IS" basis, WITHOUT
* WARRANTY OF ANY KIND, either express or implied. See the License for the specific
* language governing rights and limitations under the License.
*
* The Original Code is the Venice Web Communities System.
*
* The Initial Developer of the Original Code is Eric J. Bowersox ,
* for Silverwrist Design Studios. Portions created by Eric J. Bowersox are
* Copyright (C) 2001 Eric J. Bowersox/Silverwrist Design Studios. All Rights Reserved.
*
* Contributor(s):
*/
package com.silverwrist.util.cache;
import java.lang.ref.*;
import java.util.*;
/**
* A special kind of Map that acts as a cache of data items. The CacheMap
* uses SoftReferences, so its data values will be shed if the virtual machine needs
* more memory; also, if too many entries are added to the map, certain entries will be removed in
* accordance with the supplied or default CacheMapStrategy object.
*
* @author Eric J. Bowersox <erbo@silcom.com>
* @version X
* @see CacheMapStrategy
* @see java.util.Map
*/
public class CacheMap implements Map
{
/*--------------------------------------------------------------------------------
* Internal class used to do comparisons for cache shrinkage
*--------------------------------------------------------------------------------
*/
static final class CacheOrdering implements Comparator
{
private CacheMapStrategy strategy; // CacheMap's strategy object
private long tick; // when the sort operation started
CacheOrdering(CacheMapStrategy strategy)
{
this.strategy = strategy;
this.tick = System.currentTimeMillis();
} // end constructor
public int compare(Object o1, Object o2)
{
long figm1 = strategy.getEntryValue((CacheMapEntry)o1,tick);
long figm2 = strategy.getEntryValue((CacheMapEntry)o2,tick);
return (int)(figm1 - figm2); // we want the largest figures of merit to go first
} // end compare
public boolean equals(Object o)
{
return (o instanceof CacheOrdering);
} // end equals
} // end class CacheOrdering
/*--------------------------------------------------------------------------------
* Internal class implementing a default cache ordering strategy
*--------------------------------------------------------------------------------
*/
static final class DefaultStrategy implements CacheMapStrategy
{
private static final long SCALING_FACTOR = 5000;
DefaultStrategy()
{ // do nothing
} // end constructor
public long getEntryValue(CacheMapEntry entry, long tick)
{
return (entry.getHits() * SCALING_FACTOR) - entry.getAge(tick);
} // end getEntryValue
} // end class DefaultStrategy
/*--------------------------------------------------------------------------------
* Static data members
*--------------------------------------------------------------------------------
*/
private static final DefaultStrategy default_strategy_singleton = new DefaultStrategy();
/*--------------------------------------------------------------------------------
* Attributes
*--------------------------------------------------------------------------------
*/
private int capacity; // capacity of the CacheMap
private int shrink_percentage; // what percentage we shrink by when full
private CacheMapStrategy strategy; // strategy routine to use to purge entries
private HashMap base_map; // maps keys to CacheMapEntry values
private ArrayList element_list; // the actual elements
private ReferenceQueue rq; // holds references that the garbage collector has cleared
/*--------------------------------------------------------------------------------
* Constructors
*--------------------------------------------------------------------------------
*/
/**
* Constructs a new CacheMap.
*
* @param capacity The maximum number of entries this map can contain.
* @param shrink_percentage The percentage of entries which will be removed from the cache
* whenever it needs to shrink itself.
* @param strategy The strategy object which is used to determine which elements to remove.
* @exception java.lang.IllegalArgumentException If the specified capacity is negative or zero, or
* the shrink percentage is not in the range [1..100].
* @exception java.lang.NullPointerException If the strategy object reference is null.
*/
public CacheMap(int capacity, int shrink_percentage, CacheMapStrategy strategy)
{
if (capacity<=0)
throw new IllegalArgumentException("capacity must be greater than 0");
if ((shrink_percentage<=0) || (shrink_percentage>100))
throw new IllegalArgumentException("shrink_percentage must be in [1, 100]");
if (strategy==null)
throw new NullPointerException("no strategy passed to CacheMap");
this.capacity = capacity;
this.shrink_percentage = shrink_percentage;
this.strategy = strategy;
this.base_map = new HashMap(10);
this.element_list = new ArrayList(10);
this.rq = new ReferenceQueue();
} // end constructor
/**
* Constructs a new CacheMap with a default strategy.
*
* @param capacity The maximum number of entries this map can contain.
* @param shrink_percentage The percentage of entries which will be removed from the cache
* whenever it needs to shrink itself.
* @exception java.lang.IllegalArgumentException If the specified capacity is negative or zero, or
* the shrink percentage is not in the range [1..100].
*/
public CacheMap(int capacity, int shrink_percentage)
{
this(capacity,shrink_percentage,default_strategy_singleton);
} // end constructor
/**
* Constructs a new CacheMap with a default strategy and shrink percentage.
*
* @param capacity The maximum number of entries this map can contain.
* @exception java.lang.IllegalArgumentException If the specified capacity is negative or zero.
*/
public CacheMap(int capacity)
{
this(capacity,10,default_strategy_singleton);
} // end constructor
/*--------------------------------------------------------------------------------
* Internal operations
*--------------------------------------------------------------------------------
*/
private void doSweep()
{
Reference r = rq.poll(); // the reference that's been cleared
ArrayList ditch = new ArrayList(); // a list of entries to ditch
Iterator it; // current iterator
while (r!=null)
{ // look for the dead reference in the element list
it = element_list.iterator();
while (it.hasNext())
{ // check each cache map entry in return
CacheMapEntry ntry = (CacheMapEntry)(it.next());
if (ntry.matchReference(r))
{ // remove the offending entry and save it in the temporary list
it.remove();
ditch.add(ntry);
break;
} // end if
} // end while
r = rq.poll(); // get next dead reference
} // end while
if (ditch.isEmpty())
return; // nothing to prune
it = ditch.iterator();
while (it.hasNext())
{ // clear all entries from the base hashmap as well
CacheMapEntry ntry = (CacheMapEntry)(it.next());
base_map.remove(ntry.getKey());
ntry.discard();
} // end while
} // end doSweep
public synchronized void doShrink(int num_remove)
{
// Sort the element list to figure out which elements to remove.
Collections.sort(element_list,new CacheOrdering(strategy));
// The elements we want to remove are at the end of the array, so start from there.
for (int i=0; iInteger.MAX_VALUE elements, returns Integer.MAX_VALUE.
*
* @return The number of key-value mappings in this map.
*/
public int size()
{
doSweep();
return base_map.size();
} // end size
/**
* Returns true if this map contains no key-value mappings.
*
* @return true if this map contains no key-value mappings.
*/
public boolean isEmpty()
{
doSweep();
return base_map.isEmpty();
} // end isEmpty
/**
* Returns true if this map contains a mapping for the specified key.
*
* @param key Key whose presence in this map is to be tested.
* @return true if this map contains a mapping for the specified key.
* @exception java.lang.ClassCastException If the key is of an inappropriate type for this map.
* @exception java.lang.NullPointerException If the key is null.
*/
public boolean containsKey(Object key)
{
doSweep();
return base_map.containsKey(key);
} // end containsKey
/**
* Returns true if this map maps one or more keys to the specified value.
*
* @param value Value whose presence in this map is to be tested.
* @return true if this map maps one or more keys to the specified value.
*/
public boolean containsValue(Object value)
{
doSweep();
Iterator it = element_list.iterator();
while (it.hasNext())
{ // look at all the CacheMapEntry values we have
CacheMapEntry cme = (CacheMapEntry)(it.next());
Object my_val = cme.getValue();
if (my_val==null)
{ // test for also null
if (value==null)
return true;
} // end if
else
{ // make sure the other value is non-null before we test equality
if ((value!=null) && my_val.equals(value))
return true;
} // end else
} // end while
return false; // nope, sorry
} // end containsValue
/**
* Returns the value to which this map maps the specified key. Returns null if the map
* contains no mapping for this key.
*
* @param key Key whose associated value is to be returned.
* @return The value to which this map maps the specified key, or null if the map contains
* no mapping for this key.
* @exception java.lang.ClassCastException If the key is of an inappropriate type for this map.
* @exception java.lang.NullPointerException If the key is null.
* @see #containsKey(java.lang.Object)
*/
public Object get(Object key)
{
doSweep();
CacheMapEntry cme = (CacheMapEntry)(base_map.get(key));
if (cme==null)
return null;
cme.touch();
return cme.getValue();
} // end get
/**
* Associates the specified value with the specified key in this map. If the map previously contained
* a mapping for this key, the old value is replaced.
*
* @param key Key with which the specified value is to be associated.
* @param value Value to be associated with the specified key.
* @return The previous value associated with the specified key, or null if there was no
* mapping for the key.
* @exception java.lang.ClassCastException If the class of the specified key or value prevents it from
* being stored in this map.
* @exception java.lang.IllegalArgumentException If some aspect of this key or value prevents it from
* being stored in this map.
* @exception java.lang.NullPointerException If the specified key or value is null.
*/
public Object put(Object key, Object value)
{
doSweep();
Object rc = null;
CacheMapEntry cme = (CacheMapEntry)(base_map.get(key));
if (cme==null)
{ // create a new CacheMapEntry for this key
cme = new CacheMapEntry(key,value,rq);
synchronized (this)
{ // insert it into the basic object
if (base_map.size()==capacity)
doShrink((element_list.size() * shrink_percentage) / 100);
element_list.add(cme);
base_map.put(cme.getKey(),cme);
} // end synchronized block
} // end if
else
{ // we have an old value - replace it and touch the entry
cme.touch();
rc = cme.setValue(value,rq);
} // end else
return rc;
} // end put
/**
* Removes the mapping for this key from this map if present.
*
* @param key Key whose mapping is to be removed from the map.
* @return The previous value associated with the specified key, or null if there was no
* mapping for the key.
*/
public Object remove(Object key)
{
doSweep();
Object rc = null;
CacheMapEntry cme = (CacheMapEntry)(base_map.get(key));
if (cme!=null)
{ // save the mapped value before we remove it
rc = cme.getValue();
synchronized (this)
{ // remove the values
base_map.remove(key);
element_list.remove(cme);
} // end synchronized block
cme.discard(); // zap the reference
} // end if
return rc;
} // end remove
/**
* Copies all of the mappings from the specified map to this map. These mappings will replace any mappings
* that this map had for any of the keys currently in the specified map.
*
* @param map Mappings to be stored in this map.
* @exception java.lang.ClassCastException If the class of a key or value in the specified map prevents
* it from being stored in this map.
* @exception java.lang.IllegalArgumentException If some aspect of a key or value in the specified map
* prevents it from being stored in this map.
* @exception java.lang.NullPointerException If the specified key or value is null.
*/
public void putAll(Map map)
{
doSweep();
synchronized (this)
{ // make sure we have enough space in the CacheMap for all the new elements!
int nover = (map.size() + base_map.size()) - capacity;
if (nover>0)
doShrink(nover);
} // end synchronized block
Iterator it = map.entrySet().iterator();
while (it.hasNext())
{ // add each element in turn
Map.Entry me = (Map.Entry)(it.next());
put(me.getKey(),me.getValue());
} // end while
} // end putAll
/**
* Removes all mappings from this map.
*/
public synchronized void clear()
{
base_map.clear();
Iterator it = element_list.iterator();
while (it.hasNext())
{ // discard all entries we have
CacheMapEntry cme = (CacheMapEntry)(it.next());
cme.discard();
} // end while
element_list.clear();
} // end clear
/**
* Returns a set view of the keys contained in this map.
*
* @return A set view of the keys contained in this map.
*/
public Set keySet()
{
return base_map.keySet();
} // end keySet
/**
* Returns a collection view of the values contained in this map.
*
* @return A collection view of the values contained in this map.
* @exception java.lang.UnsupportedOperationException This map does not support this operation.
*/
public Collection values()
{
throw new UnsupportedOperationException("CacheMap.values() is not implemented");
} // end values
/**
* Returns a set view of the mappings contained in this map.
*
* @return A set view of the mappings contained in this map.
* @exception java.lang.UnsupportedOperationException This map does not support this operation.
*/
public Set entrySet()
{
throw new UnsupportedOperationException("CacheMap.entrySet() is not implemented");
} // end entrySet
/**
* Compares the specified object with this map for equality. Returns true if the given object
* is also a map and the two Maps represent the same mappings.
*
* @param o Object to be compared for equality with this map.
* @return true if the specified object is equal to this map.
*/
public boolean equals(Object o)
{
if ((o==null) || !(o instanceof Map))
return false; // not a map
doSweep();
Map other = (Map)o;
if (other.size()!=base_map.size())
return false; // size does matter!
Iterator it = base_map.values().iterator();
while (it.hasNext())
{ // get each of the entries out and use that to do a key-value comparison
CacheMapEntry cme = (CacheMapEntry)(it.next());
Object o1 = cme.getValue();
Object o2 = other.get(cme.getKey());
if (o1==null)
{ // must have a matching null
if (o2!=null)
return false;
} // end if
else
{ // make sure we have a matching object (not null)
if ((o2==null) || !(o2.equals(o1)))
return false;
} // end else
} // end while
return true; // all OK!
} // end equals
/**
* Returns the hash code value for this map. The hash code of a map is defined to be the sum of the
* hash codes of each entry in the map's entrySet view.
*
* @return The hash code value for this map.
* @see #equals(java.lang.Object)
* @see CacheMapEntry#hashCode()
*/
public int hashCode()
{
doSweep();
int rc = 0;
Iterator it = base_map.values().iterator();
while (it.hasNext())
{ // add up the hash codes and return them
CacheMapEntry cme = (CacheMapEntry)(it.next());
rc += cme.hashCode();
} // end while
return rc;
} // end hashCode
/*--------------------------------------------------------------------------------
* External getters/setters
*--------------------------------------------------------------------------------
*/
/**
* Returns the capacity of this cache map.
*
* @return The capacity of this cache map.
*/
public int getCapacity()
{
return capacity;
} // end getCapacity
/**
* Sets the capacity of this cache map.
*
* @param c The new capacity for this cache map.
* @exception java.lang.IllegalArgumentException If the specified capacity is negative or zero.
*/
public void setCapacity(int c)
{
if (c<=0)
throw new IllegalArgumentException("capacity must be greater than 0");
capacity = c;
} // end setCapacity
/**
* Returns the shrink percentage of this cache map.
*
* @return The shrink percentage of this cache map.
*/
public int getShrinkPercentage()
{
return shrink_percentage;
} // end getShrinkPercentage
/**
* Sets the shrink percentage of this cache map.
*
* @param p The new shrink percentage for this cache map.
* @exception java.lang.IllegalArgumentException If the specified shrink percentage is not in the
* range [1..100].
*/
public void setShrinkPercentage(int p)
{
if ((p<=0) || (p>100))
throw new IllegalArgumentException("shrink_percentage must be in [1, 100]");
shrink_percentage = p;
} // end setShrinkPercentage
/**
* Returns the strategy object associated with the cache map.
*
* @return The strategy object associated with the cache map.
*/
public CacheMapStrategy getStrategy()
{
return strategy;
} // end getStrategy
/**
* Sets the strategy object associated with this cache map.
*
* @param s The new strategy object to be associated with the cache map.
* @exception java.lang.NullPointerException If the strategy object reference is null.
*/
public void setStrategy(CacheMapStrategy s)
{
if (s==null)
throw new NullPointerException("no strategy passed to CacheMap");
strategy = s;
} // end setStrategy
/*--------------------------------------------------------------------------------
* External operations
*--------------------------------------------------------------------------------
*/
/**
* Causes the current size of the cache map to shrink by at least the shrink percentage specified
* in the constructor or in setShrinkPercentage. Cached items already reclaimed by the
* garbage collector are stripped out first.
*/
public synchronized void shrink()
{
// Figure out how many elements to remove.
int num_remove = (element_list.size() * shrink_percentage) / 100;
// Try a sweep first.
int n1 = base_map.size();
doSweep();
n1 -= base_map.size();
if (n1