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/**
* Copyright 2000-2001 by iPlanet/Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*/
package com.sun.appserv.util.cache;
import java.text.MessageFormat;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Vector;
import java.util.Map;
import java.util.HashMap;
import java.util.Properties;
import java.util.Iterator;
import java.util.ResourceBundle;
import com.sun.common.util.logging.LogDomains;
/**
* BaseCache
* Generic in-memory, abstract cache
*/
public class BaseCache implements Cache {
/**
* The resource bundle containing the localized message strings.
*/
protected static ResourceBundle _rb = null;
static final int MAX_ENTRIES = 1 << 30;
static final float DEFAULT_LOAD_FACTOR = 0.75f;
// maximum number of entries this cache may ever hold
int maxEntries;
// the number of cache entries in this cache
protected int entryCount;
private Object entryCountLk = new Object();
/** threshold for the cache; once the threshold is reached
* entries are removed to accomodate newer inserts
*/
protected int threshold = 0;
// the number of cache hits
private int hitCount;
private Object hitCountLk = new Object();
// the number of cache misses
private int missCount;
private Object missCountLk = new Object();
// the number of cache item removals
private int removalCount;
private Object removalCountLk = new Object();
// the number of cache item refreshes
private int refreshCount;
private Object refreshCountLk = new Object();
// the number of times an item was added to cache
private int addCount;
private Object addCountLk = new Object();
// the number of times the cache overflowed
private int overflowCount;
private Object overflowCountLk = new Object();
// table size
protected int maxBuckets;
// cache entries hash table
protected CacheItem[] buckets;
// bucket-wide locks
protected Object[] bucketLocks;
// boolean status and locks for item thread-safe refreshes
protected boolean[] refreshFlags;
protected ArrayList listeners = new ArrayList();
/**
* default constructor for the basic cache
*/
public BaseCache() { }
/**
* initialize the cache
* @param maxEntries maximum number of entries expected in the cache
* @param props opaque list of properties for a given cache implementation
* @throws a generic Exception if the initialization failed
*/
public void init(int maxEntries, Properties props) throws Exception {
init(maxEntries, DEFAULT_LOAD_FACTOR, props);
}
/**
* initialize the cache
* @param maxEntries maximum number of entries expected in the cache
* @param loadFactor the load factor
* @param props opaque list of properties for a given cache implementation
* @throws a generic Exception if the initialization failed
*/
public void init(int maxEntries, float loadFactor, Properties props) {
// web container logger
_rb = LogDomains.getLogger(LogDomains.CMN_LOGGER).getResourceBundle();
if (maxEntries <= 0) {
String msg = _rb.getString("cache.BaseCache.illegalMaxEntries");
Integer obj = Integer.valueOf(maxEntries);
Object[] params = { obj };
msg = MessageFormat.format(msg, params);
throw new IllegalArgumentException(msg);
}
if (maxEntries > MAX_ENTRIES)
maxEntries = MAX_ENTRIES;
this.maxEntries = maxEntries;
// find a power of 2 >= maxEntries
maxBuckets = 1;
while (maxBuckets < maxEntries)
maxBuckets <<= 1;
//Cannot have the loadfactor as a negative value
if( loadFactor < 0 )
loadFactor = 0;
/** initialize the threshold; a zero value for maxEntries
* implies no caching.
*/
if (maxEntries != 0) {
threshold = (int)(maxEntries * loadFactor) + 1;
}
// create the cache and the bucket locks
entryCount = 0;
buckets = new CacheItem[maxBuckets];
bucketLocks = new Object[maxBuckets];
refreshFlags = new boolean[maxBuckets];
for (int i=0; i<maxBuckets; i++) {
buckets[i] = null;
bucketLocks[i] = new Object();
refreshFlags[i] = false;
}
}
/**
* add the cache module listener
* @param listener <code>CacheListener</code> implementation
*/
public void addCacheListener(CacheListener listener) {
listeners.add(listener);
}
/**
* Returns a hash code for non-null Object x.
* @See also <code>HashMap</code>
*/
protected int hash(Object x) {
int h = x.hashCode();
return h - (h << 7); // i.e., -127 * h
}
/**
* Check for equality of non-null reference x and possibly-null y.
*/
protected boolean eq(Object x, Object y) {
return x == y || x.equals(y);
}
/**
* increase the threshold
*/
protected void handleOverflow() {
// just double the threshold; this may degenerate the cache.
threshold = (threshold * 2);
incrementOverflowCount();
}
/**
* this item is just added to the cache
* @param item <code>CacheItem</code> that was created
* @return a overflow item; may be null
* Cache bucket is already synchronized by the caller
*
* Here, if cache is overflowing (i.e. reached threshold); this class
* simply makes the cache unbounded by raising the threshold. Subclasses
* are expected to provide a robust cache replacement algorithm.
*
* Subclasses should enhance this implemntation.
*/
protected CacheItem itemAdded(CacheItem item) {
if (isThresholdReached()) {
handleOverflow();
}
return null;
}
/**
* this item is accessed
* @param item <code>CacheItem</code> accessed
*
* Cache bucket is already synchronized by the caller
*/
protected void itemAccessed(CacheItem item) { }
/**
* item value has been refreshed
* @param item <code>CacheItem</code> that was refreshed
* @param oldSize size of the previous value that was refreshed
* Cache bucket is already synchronized by the caller
*/
protected void itemRefreshed(CacheItem item, int oldSize) { }
/**
* item value has been removed from the cache
* @param item <code>CacheItem</code> that was just removed
*
* Cache bucket is already synchronized by the caller
*/
protected void itemRemoved(CacheItem item) { }
/**
* Cannot find an item with the given key and hashCode
* @param key <code>Object</code> that is not found
* @param hashCode <code>int</code> its hashCode
*
* @returns the Object value associated with the item
* Cache bucket is already synchronized by the caller
*/
protected Object loadValue(Object key, int hashCode) {
return null;
}
/**
* create new item
* @param hashCode for the entry
* @param key <code>Object</code> key
* @param value <code>Object</code> value
* @param size size in bytes of the item
* subclasses may override to provide their own CacheItem extensions
* e.g. one that permits persistence.
*/
protected CacheItem createItem(int hashCode, Object key,
Object value, int size) {
return new CacheItem(hashCode, key, value, size);
}
/**
* has cache reached its threshold
* @return true when the cache reached its threshold
*/
protected boolean isThresholdReached() {
return (entryCount > threshold);
}
/**
* get the index of the item in the cache
* @param hashCode of the entry
* @return the index to be used in the cache
*/
protected final int getIndex(int hashCode) {
return (hashCode & (maxBuckets - 1));
}
/**
* get the index of the item given a key
* @param key of the entry
* @return the index to be used in the cache
*/
public final int getIndex(Object key) {
return getIndex(hash(key));
}
/**
* get the item stored at the key.
* @param key lookup key
* @returns the item stored at the key; null if not found.
*/
public Object get(Object key) {
int hashCode = hash(key);
return get(hashCode, key);
}
/**
* get the item stored at the given pre-computed hash code and the key.
* @param key lookup key
* @returns the item stored at the key; null if not found.
*/
public Object get(int hashCode, Object key) {
int index = getIndex(hashCode);
Object value;
CacheItem item = null;
synchronized (bucketLocks[index]) {
item = buckets[index];
for (; item != null; item = item.next) {
if ( (hashCode == item.hashCode) && eq(key, item.key) ) {
break;
}
}
// update the stats in line
if (item != null) {
value = item.getValue();
itemAccessed(item);
}
else
value = loadValue(key, hashCode);
}
if (item != null)
incrementHitCount();
else
incrementMissCount();
return value;
}
/**
* check if the cache contains the item at the key
* @param key lookup key
* @returns true if there is an item stored at the key; false if not.
*/
public boolean contains(Object key) {
return (get(key) != null);
}
/**
* get all the items stored at the key.
* @param key lookup key
* @returns an Iterator over the items with the given key.
*/
public Iterator getAll(Object key) {
int hashCode = hash(key);
int index = getIndex(hashCode);
ArrayList valueList = new ArrayList(entryCount);
synchronized (bucketLocks[index]) {
CacheItem item = buckets[index];
for (; item != null; item = item.next) {
if ( (hashCode == item.hashCode) && eq(key, item.key) ) {
incrementHitCount();
valueList.add(item.getValue());
}
}
}
return valueList.iterator();
}
/**
* get an Iterator for the keys stored in the cache
* @returns an Iterator
*/
public Iterator keys() {
ArrayList keyList = new ArrayList(entryCount);
for (int index=0; index < maxBuckets; index++) {
synchronized (bucketLocks[index]) {
for (CacheItem item = buckets[index]; item != null;
item = item.next) {
keyList.add(item.key);
}
}
}
return keyList.iterator();
}
/**
* get an Enumeration for the keys stored in the cache
* @returns an Enumeration
* XXX: should use Iterator which is based on Collections
*/
public Enumeration elements() {
Vector keyList = new Vector();
for (int index=0; index < maxBuckets; index++) {
synchronized (bucketLocks[index]) {
for (CacheItem item = buckets[index]; item != null;
item = item.next) {
keyList.addElement(item.key);
}
}
}
return keyList.elements();
}
/**
* get an Iterator for the values stored in the cache
* @returns an Iterator
*/
public Iterator values() {
ArrayList valueList = new ArrayList(entryCount);
for (int index=0; index < maxBuckets; index++) {
synchronized (bucketLocks[index]) {
for (CacheItem item = buckets[index]; item != null;
item = item.next) {
valueList.add(item.value);
}
}
}
return valueList.iterator();
}
/**
/**
* cache the given value at the specified key and return previous value
* @param key lookup key
* @param object item value to be stored
* @returns the previous item stored at the key; null if not found.
*/
public Object put(Object key, Object value) {
int hashCode = hash(key);
return _put(hashCode, key, value, -1, false);
}
/**
* cache the given value at the specified key and return previous value
* @param key lookup key
* @param object item value to be stored
* @param size in bytes of the value being cached
* @returns the previous item stored at the key; null if not found.
*/
public Object put(Object key, Object value, int size) {
int hashCode = hash(key);
return _put(hashCode, key, value, size, false);
}
/**
* add the given value to the cache at the specified key
* @param key lookup key
* @param object item value to be stored
*/
public void add(Object key, Object value) {
int hashCode = hash(key);
_put(hashCode, key, value, -1, true);
}
/**
* add the given value with specified size to the cache at specified key
* @param key lookup key
* @param object item value to be stored
* @param size in bytes of the value being added
*
* This function is suitable for multi-valued keys.
*/
public void add(Object key, Object value, int size) {
int hashCode = hash(key);
_put(hashCode, key, value, size, true);
}
/**
* cache the given value at the specified key and return previous value
* @param hashCode previously computed hashCode for the key
* @param key lookup key
* @param object item value to be stored
* @param size in bytes of the value being cached
* @param addValue treate this operation to add (default is to replace)
* @returns the previous item stored at the key; null if not found.
*
* Note: This can be used just to refresh the cached item as well, altho
* it may call trimCache() if the cache reached its threshold -- which is
* is probably not very intuitive.
*/
protected Object _put(int hashCode, Object key,
Object value, int size, boolean addValue) {
int index = getIndex(hashCode);
CacheItem item, newItem = null, oldItem = null, overflow = null;
Object oldValue;
int oldSize = 0;
// lookup the item
synchronized (bucketLocks[index]) {
for (item = buckets[index]; item != null; item = item.next) {
if ((hashCode == item.hashCode) && eq(key, item.key)) {
oldItem = item;
break;
}
}
// if there was no item in the cache, insert the given item
if (addValue || oldItem == null) {
newItem = createItem(hashCode, key, value, size);
// add the item at the head of the bucket list
newItem.next = buckets[index];
buckets[index] = newItem;
oldValue = null;
overflow = itemAdded(newItem);
}
else {
oldSize = oldItem.getSize();
oldValue = oldItem.refreshValue(value, size);
itemRefreshed(oldItem, oldSize);
}
}
if (newItem != null) {
incrementEntryCount();
incrementAddCount();
// make sure we are are not crossing the threshold
if (overflow != null)
trimItem(overflow);
}
else
incrementRefreshCount();
return oldValue;
}
/**
* remove the item stored at the key.
* @param key lookup key
* @returns the item stored at the key; null if not found.
*/
public Object remove(Object key) {
int hashCode = hash(key);
Object retVal = null;
CacheItem removed = _remove( hashCode, key, null);
if (removed != null)
retVal = removed.getValue();
return retVal;
}
/**
* remove the item stored at the key.
* @param hashCode a precomputed hashCode
* @param key lookup key
* @returns the item stored at the key; null if not found.
*/
public Object remove(int hashCode, Object key) {
Object retVal = null;
CacheItem removed = _remove( hashCode, key, null);
if (removed != null)
retVal = removed.getValue();
return retVal;
}
/**
* remove the given value stored at the key; value-specific removals.
* @param key lookup key
* @param value to match (for a multi-valued keys)
* @returns the item stored at the key; null if not found.
*/
public Object remove(Object key, Object value) {
int hashCode = hash(key);
Object retVal = null;
CacheItem removed = _remove( hashCode, key, value);
if (removed != null)
retVal = removed.getValue();
return retVal;
}
/**
* remove the item stored at the key.
* @param hashCode a precomputed hashCode
* @param key lookup key
* @param value of the item to be matched
* @returns the item stored at the key; null if not found.
*/
protected CacheItem _remove(int hashCode, Object key, Object value) {
int index = getIndex(hashCode);
CacheItem prev = null, item = null;
synchronized (bucketLocks[index]) {
for (item = buckets[index]; item != null; item = item.next) {
if (hashCode == item.hashCode && key.equals(item.key)) {
if (value == null || value == item.value) {
if (prev == null) {
buckets[index] = item.next;
} else {
prev.next = item.next;
}
item.next = null;
itemRemoved(item);
break;
}
}
prev = item;
}
}
if (item != null) {
decrementEntryCount();
incrementRemovalCount();
incrementHitCount();
} else
incrementMissCount();
return item;
}
/**
* remove the item stored at the key.
* @param item CacheItem to be removed
* @return the item stored at the key; null if not found.
*/
protected CacheItem _removeItem(CacheItem ritem) {
int index = getIndex(ritem.hashCode);
CacheItem prev = null, item = null;
synchronized (bucketLocks[index]) {
for (item = buckets[index]; item != null; item = item.next) {
if (item == ritem) {
if (prev == null) {
buckets[index] = item.next;
} else {
prev.next = item.next;
}
item.next = null;
break;
}
prev = item;
}
}
if (item != null) {
decrementEntryCount();
}
return item;
}
/**
* remove all the item with the given key.
* @param key lookup key
*/
public void removeAll(Object key) {
int hashCode = hash(key);
int index = getIndex(hashCode);
CacheItem prev = null, item = null;
ArrayList items = new ArrayList(entryCount);
synchronized (bucketLocks[index]) {
for (item = buckets[index]; item != null;
item = item.next) {
if (hashCode == item.hashCode && key.equals(item.key)) {
if (prev == null) {
buckets[index] = item.next;
} else {
prev.next = item.next;
}
item.next = null;
decrementEntryCount();
incrementRemovalCount();
items.add(item);
}
prev = item;
}
}
// notify subclasses
for (int i = 0; i < items.size(); i++) {
itemRemoved((CacheItem)items.get(i));
}
}
/**
* trim the item from the cache and notify listeners
* @param item to be trimmed
*/
protected void trimItem(CacheItem item) {
CacheItem removed = _removeItem(item);
if (removed != null) {
for (int i = 0; i < listeners.size(); i++) {
CacheListener listener = (CacheListener) listeners.get(i);
listener.trimEvent(removed.key, removed.value);
}
}
}
/**
* wait for a refresh on the object associated with the key
* @param key lookup key
* @returns true on successful notification, or false if there is
* no thread refreshing this entry.
*/
public boolean waitRefresh(int index) {
synchronized (bucketLocks[index]) {
if (refreshFlags[index] == false) {
refreshFlags[index] = true;
return false;
}
// wait till refresh is finished
try {
bucketLocks[index].wait();
} catch (InterruptedException ie) {}
}
return true;
}
/**
* notify threads waiting for a refresh on the object associated with the key
* @param key lookup key
*/
public void notifyRefresh(int index) {
// notify other threads waiting for refresh
synchronized (bucketLocks[index]) {
refreshFlags[index] = false;
bucketLocks[index].notifyAll();
}
}
/**
* clear all the entries from the cache.
* @returns the number of entries cleared from the cache
*/
public int clear() {
CacheItem item=null, next=null;
int count = 0;
for (int index = 0; index < maxBuckets; index++) {
synchronized (bucketLocks[index]) {
for (item = buckets[index]; item != null;
item = item.next) {
next = item.next;
item.next = null;
count++;
decrementEntryCount();
itemRemoved(item);
if (entryCount == 0)
break;
}
buckets[index] = null;
}
}
return count;
}
/**
* trim the expired entries from the cache.
* @param maxCount maximum number of invalid entries to trim
* specify Integer.MAX_VALUE to trim all timedout entries
*
* This call is to be scheduled by a thread managed by the container.
*/
public void trimExpiredEntries(int maxCount) {}
/**
* get the number of entries in the cache
* @return the number of entries the cache currently holds
*/
public int getEntryCount() {
return entryCount;
}
/*** methods for monitoring the cache ***/
/**
* is this cache empty?
* @returns true if the cache is empty; false otherwise.
*/
public boolean isEmpty() {
return (entryCount == 0);
}
/**
* synchronized counter updates
*/
protected final void incrementEntryCount() {
synchronized(entryCountLk) {
entryCount++;
}
}
protected final void decrementEntryCount() {
synchronized(entryCountLk) {
entryCount--;
}
}
protected final void incrementHitCount() {
synchronized (hitCountLk) {
hitCount++;
}
}
protected final void incrementMissCount() {
synchronized (missCountLk) {
missCount++;
}
}
protected final void incrementRemovalCount() {
synchronized (removalCountLk) {
removalCount++;
}
}
protected final void incrementRefreshCount() {
synchronized (refreshCountLk) {
refreshCount++;
}
}
protected final void incrementAddCount() {
synchronized (addCountLk) {
addCount++;
}
}
protected final void incrementOverflowCount() {
synchronized (overflowCountLk) {
overflowCount++;
}
}
/**
* get generic stats from subclasses
*/
/**
* get the desired statistic counter
* @param key to corresponding stat
* @return an Object corresponding to the stat
* See also: Constant.java for the key
*/
public Object getStatByName(String key) {
Object stat = null;
if (key == null)
return null;
if (key.equals(Constants.STAT_BASECACHE_MAX_ENTRIES))
stat = Integer.valueOf(maxEntries);
else if (key.equals(Constants.STAT_BASECACHE_THRESHOLD))
stat = Integer.valueOf(threshold);
else if (key.equals(Constants.STAT_BASECACHE_TABLE_SIZE))
stat = Integer.valueOf(maxBuckets);
else if (key.equals(Constants.STAT_BASECACHE_ENTRY_COUNT))
stat = Integer.valueOf(entryCount);
else if (key.equals(Constants.STAT_BASECACHE_HIT_COUNT))
stat = Integer.valueOf(hitCount);
else if (key.equals(Constants.STAT_BASECACHE_MISS_COUNT))
stat = Integer.valueOf(missCount);
else if (key.equals(Constants.STAT_BASECACHE_REMOVAL_COUNT))
stat = Integer.valueOf(removalCount);
else if (key.equals(Constants.STAT_BASECACHE_REFRESH_COUNT))
stat = Integer.valueOf(refreshCount);
else if (key.equals(Constants.STAT_BASECACHE_OVERFLOW_COUNT))
stat = Integer.valueOf(overflowCount);
else if (key.equals(Constants.STAT_BASECACHE_ADD_COUNT))
stat = Integer.valueOf(addCount);
return stat;
}
/**
* get the stats snapshot
* @return a Map of stats
* See also: Constant.java for the keys
*/
public Map getStats() {
HashMap stats = new HashMap();
stats.put(Constants.STAT_BASECACHE_MAX_ENTRIES,
Integer.valueOf(maxEntries));
stats.put(Constants.STAT_BASECACHE_THRESHOLD,
Integer.valueOf(threshold));
stats.put(Constants.STAT_BASECACHE_TABLE_SIZE,
Integer.valueOf(maxBuckets));
stats.put(Constants.STAT_BASECACHE_ENTRY_COUNT,
Integer.valueOf(entryCount));
stats.put(Constants.STAT_BASECACHE_HIT_COUNT,
Integer.valueOf(hitCount));
stats.put(Constants.STAT_BASECACHE_MISS_COUNT,
Integer.valueOf(missCount));
stats.put(Constants.STAT_BASECACHE_REMOVAL_COUNT,
Integer.valueOf(removalCount));
stats.put(Constants.STAT_BASECACHE_REFRESH_COUNT,
Integer.valueOf(refreshCount));
stats.put(Constants.STAT_BASECACHE_OVERFLOW_COUNT,
Integer.valueOf(overflowCount));
stats.put(Constants.STAT_BASECACHE_ADD_COUNT,
Integer.valueOf(addCount));
return stats;
}
/**
* Sets all references to null. This method should be called
* at the end of this object's life cycle.
*/
public void destroy() {
if ((listeners != null) && (buckets != null) && (bucketLocks != null)) {
clear();
listeners.clear();
}
entryCountLk = null;
hitCountLk = null;
missCountLk = null;
removalCountLk = null;
refreshCountLk = null;
addCountLk = null;
overflowCountLk = null;
buckets = null;
bucketLocks = null;
refreshFlags = null;
listeners = null;
}
/**
* clear the stats
*/
public void clearStats() {
hitCount = 0;
missCount = 0;
removalCount = 0;
refreshCount = 0;
overflowCount = 0;
addCount = 0;
}
/** default CacheItem class implementation ***/
protected static class CacheItem {
int hashCode;
Object key;
Object value;
int size;
CacheItem next;
protected CacheItem(int hashCode, Object key, Object value, int size) {
this.hashCode = hashCode;
this.key = key;
this.value = value;
this.size = size;
}
/**
* get the item's hashCode
*/
protected int getHashCode() {
return hashCode;
}
/**
* get the item's key
*/
protected Object getKey() {
return key;
}
/**
* get the item's value
*/
protected Object getValue() {
return value;
}
/**
* @return size of the entry in bytes
* a value of -1 indicates unknown size
*/
protected int getSize() {
return size;
}
/**
* refresh the item's value
* @param value value to be updated
* @param newSize of the field
*/
protected Object refreshValue(Object value, int newSize) {
Object oldValue = this.value;
this.value = value;
this.size = newSize;
return oldValue;
}
public String toString() {
return "key: " + key + "; value: " + value.toString();
}
}
}
|
