/*******************************************************************************
* Copyright (c) 2002, 2008 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Rational Software - Initial API and implementation
*******************************************************************************/
package org.eclipse.cdt.internal.core.util;
import java.util.Enumeration;
/**
* The <code>OverflowingLRUCache</code> is an LRUCache which attempts
* to maintain a size equal or less than its <code>fSpaceLimit</code>
* by removing the least recently used elements.
*
* <p>The cache will remove elements which successfully close and all
* elements which are explicitly removed.
*
* <p>If the cache cannot remove enough old elements to add new elements
* it will grow beyond <code>fSpaceLimit</code>. Later, it will attempt to
* shink back to the maximum space limit.
*
* The method <code>close</code> should attempt to close the element. If
* the element is successfully closed it will return true and the element will
* be removed from the cache. Otherwise the element will remain in the cache.
*
* <p>The cache implicitly attempts shrinks on calls to <code>put</code>and
* <code>setSpaceLimit</code>. Explicitly calling the <code>shrink</code> method
* will also cause the cache to attempt to shrink.
*
* <p>The cache calculates the used space of all elements which implement
* <code>ILRUCacheable</code>. All other elements are assumed to be of size one.
*
* <p>Use the <code>#peek(Object)</code> and <code>#disableTimestamps()</code> method to
* circumvent the timestamp feature of the cache. This feature is intended to be used
* only when the <code>#close(LRUCacheEntry)</code> method causes changes to the cache.
* For example, if a parent closes its children when </code>#close(LRUCacheEntry)</code> is called,
* it should be careful not to change the LRU linked list. It can be sure it is not causing
* problems by calling <code>#peek(Object)</code> instead of <code>#get(Object)</code> method.
*
* @see LRUCache
*
* This class is similar to the JDT OverflowingLRUCache class.
*/
public abstract class OverflowingLRUCache<K,T> extends LRUCache<K,T> {
/**
* Indicates if the cache has been over filled and by how much.
*/
protected int fOverflow = 0;
/**
* Indicates whether or not timestamps should be updated
*/
protected boolean fTimestampsOn = true;
/**
* Indicates how much space should be reclaimed when the cache overflows.
* Inital load factor of one third.
*/
protected double fLoadFactor = 0.333;
/**
* Creates an OverflowingLRUCache with default sizes.
*
* This is required to create a cache with a hash map that is not
* dependent on the initial size of the cache (i.e. if the cache is
* relative to size of entries and not the number of entries).
*/
public OverflowingLRUCache() {
super();
}
/**
* Creates a OverflowingLRUCache.
* @param size Size limit of cache.
*/
public OverflowingLRUCache(int size) {
this(size, 0);
}
/**
* Creates a OverflowingLRUCache.
* @param size Size limit of cache.
* @param overflow Size of the overflow.
*/
public OverflowingLRUCache(int size, int overflow) {
super(size);
fOverflow = overflow;
}
/**
* Returns a new cache containing the same contents.
*
* @return New copy of this object.
*/
@Override
public Object clone() {
OverflowingLRUCache<K,T> newCache = newInstance(fSpaceLimit, fOverflow);
LRUCacheEntry<K,T> qEntry;
/* Preserve order of entries by copying from oldest to newest */
qEntry = this.fEntryQueueTail;
while (qEntry != null) {
newCache.privateAdd (qEntry._fKey, qEntry._fValue, qEntry._fSpace);
qEntry = qEntry._fPrevious;
}
return newCache;
}
/**
* Returns true if the element is successfully closed and
* removed from the cache, otherwise false.
*
* <p>NOTE: this triggers an external remove from the cache
* by closing the obejct.
*
*/
protected abstract boolean close(LRUCacheEntry<K,T> entry);
/**
* Returns an enumerator of the values in the cache with the most
* recently used first.
*/
public Enumeration<T> elements() {
if (fEntryQueue == null)
return new LRUCacheEnumerator<T>(null);
LRUCacheEnumerator.LRUEnumeratorElement<T> head =
new LRUCacheEnumerator.LRUEnumeratorElement<T>(fEntryQueue._fValue);
LRUCacheEntry<K,T> currentEntry = fEntryQueue._fNext;
LRUCacheEnumerator.LRUEnumeratorElement<T> currentElement = head;
while(currentEntry != null) {
currentElement.fNext = new LRUCacheEnumerator.LRUEnumeratorElement<T>(currentEntry._fValue);
currentElement = currentElement.fNext;
currentEntry = currentEntry._fNext;
}
return new LRUCacheEnumerator<T>(head);
}
public double fillingRatio() {
return (fCurrentSpace + fOverflow) * 100.0 / fSpaceLimit;
}
/**
* For internal testing only.
* This method exposed only for testing purposes!
*
* @return Hashtable of entries
*/
public java.util.Hashtable<K,LRUCacheEntry<K,T>> getEntryTable() {
return fEntryTable;
}
/**
* Returns the load factor for the cache. The load factor determines how
* much space is reclaimed when the cache exceeds its space limit.
* @return double
*/
public double getLoadFactor() {
return fLoadFactor;
}
/**
* @return The space by which the cache has overflown.
*/
public int getOverflow() {
return fOverflow;
}
/**
* Ensures there is the specified amount of free space in the receiver,
* by removing old entries if necessary. Returns true if the requested space was
* made available, false otherwise. May not be able to free enough space
* since some elements cannot be removed until they are saved.
*
* @param space Amount of space to free up
*/
@Override
protected boolean makeSpace(int space) {
int limit = fSpaceLimit;
if (fOverflow == 0) {
/* if space is already available */
if (fCurrentSpace + space <= limit) {
return true;
}
}
/* Free up space by removing oldest entries */
int spaceNeeded = (int)((1 - fLoadFactor) * fSpaceLimit);
spaceNeeded = (spaceNeeded > space) ? spaceNeeded : space;
LRUCacheEntry<K,T> entry = fEntryQueueTail;
while (fCurrentSpace + spaceNeeded > limit && entry != null) {
this.privateRemoveEntry(entry, false, false);
entry = entry._fPrevious;
}
/* check again, since we may have aquired enough space */
if (fCurrentSpace + space <= limit) {
fOverflow = 0;
return true;
}
/* update fOverflow */
fOverflow = fCurrentSpace + space - limit;
return false;
}
/**
* Returns a new instance of the reciever.
*/
protected abstract OverflowingLRUCache<K,T> newInstance(int size, int overflow);
/**
* Answers the value in the cache at the given key.
* If the value is not in the cache, returns null
*
* This function does not modify timestamps.
*/
public T peek(K key) {
LRUCacheEntry<K,T> entry = fEntryTable.get(key);
if (entry == null) {
return null;
}
return entry._fValue;
}
/**
* For testing purposes only
*/
public void printStats() {
int forwardListLength = 0;
LRUCacheEntry<K,T> entry = fEntryQueue;
while(entry != null) {
forwardListLength++;
entry = entry._fNext;
}
System.out.println("Forward length: " + forwardListLength); //$NON-NLS-1$
int backwardListLength = 0;
entry = fEntryQueueTail;
while(entry != null) {
backwardListLength++;
entry = entry._fPrevious;
}
System.out.println("Backward length: " + backwardListLength); //$NON-NLS-1$
Enumeration<K> keys = fEntryTable.keys();
class Temp {
public Class<?> fClass;
public int fCount;
public Temp(Class<?> aClass) {
fClass = aClass;
fCount = 1;
}
@Override
public String toString() {
return "Class: " + fClass + " has " + fCount + " entries."; //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-1$
}
}
java.util.HashMap<Class<?>, Temp> h = new java.util.HashMap<Class<?>, Temp>();
while(keys.hasMoreElements()) {
entry = fEntryTable.get(keys.nextElement());
Class<?> key = entry._fValue.getClass();
Temp t = h.get(key);
if (t == null) {
h.put(key, new Temp(key));
} else {
t.fCount++;
}
}
for (Object element : h.keySet()) {
System.out.println(h.get(element));
}
}
/**
* Removes the entry from the entry queue.
* Calls <code>privateRemoveEntry</code> with the external functionality enabled.
*
* @param shuffle indicates whether we are just shuffling the queue
* (i.e., the entry table is left alone).
*/
@Override
protected void privateRemoveEntry (LRUCacheEntry<K,T> entry, boolean shuffle) {
privateRemoveEntry(entry, shuffle, true);
}
/**
* Removes the entry from the entry queue. If <i>external</i> is true, the entry is removed
* without checking if it can be removed. It is assumed that the client has already closed
* the element it is trying to remove (or will close it promptly).
*
* If <i>external</i> is false, and the entry could not be closed, it is not removed and the
* pointers are not changed.
*
* @param shuffle indicates whether we are just shuffling the queue
* (i.e., the entry table is left alone).
*/
protected void privateRemoveEntry(LRUCacheEntry<K, T> entry, boolean shuffle, boolean external) {
if (!shuffle) {
if (external) {
fEntryTable.remove(entry._fKey);
fCurrentSpace -= entry._fSpace;
privateNotifyDeletionFromCache(entry);
} else {
if (!close(entry)) return;
// buffer close will recursively call #privateRemoveEntry with external==true
// thus entry will already be removed if reaching this point.
if (fEntryTable.get(entry._fKey) == null){
return;
}
// basic removal
fEntryTable.remove(entry._fKey);
fCurrentSpace -= entry._fSpace;
privateNotifyDeletionFromCache(entry);
}
}
LRUCacheEntry<K, T> previous = entry._fPrevious;
LRUCacheEntry<K, T> next = entry._fNext;
/* if this was the first entry */
if (previous == null) {
fEntryQueue = next;
} else {
previous._fNext = next;
}
/* if this was the last entry */
if (next == null) {
fEntryQueueTail = previous;
} else {
next._fPrevious = previous;
}
}
/**
* Sets the value in the cache at the given key. Returns the value.
*
* @param key Key of object to add.
* @param value Value of object to add.
* @return added value.
*/
@Override
public T put(K key, T value) {
/* attempt to rid ourselves of the overflow, if there is any */
if (fOverflow > 0)
shrink();
/* Check whether there's an entry in the cache */
int newSpace = spaceFor (key, value);
LRUCacheEntry<K, T> entry = fEntryTable.get (key);
if (entry != null) {
/**
* Replace the entry in the cache if it would not overflow
* the cache. Otherwise flush the entry and re-add it so as
* to keep cache within budget
*/
int oldSpace = entry._fSpace;
int newTotal = fCurrentSpace - oldSpace + newSpace;
if (newTotal <= fSpaceLimit) {
updateTimestamp (entry);
entry._fValue = value;
entry._fSpace = newSpace;
fCurrentSpace = newTotal;
fOverflow = 0;
return value;
}
privateRemoveEntry (entry, false, false);
}
// attempt to make new space
makeSpace(newSpace);
// add without worring about space, it will
// be handled later in a makeSpace call
privateAdd (key, value, newSpace);
return value;
}
/**
* Removes and returns the value in the cache for the given key.
* If the key is not in the cache, returns null.
*
* @param key Key of object to remove from cache.
* @return Value removed from cache.
*/
public Object remove(K key) {
return removeKey(key);
}
/**
* Sets the load factor for the cache. The load factor determines how
* much space is reclaimed when the cache exceeds its space limit.
* @param newLoadFactor double
* @throws IllegalArgumentException when the new load factor is not in (0.0, 1.0]
*/
public void setLoadFactor(double newLoadFactor) throws IllegalArgumentException {
if(newLoadFactor <= 1.0 && newLoadFactor > 0.0)
fLoadFactor = newLoadFactor;
else
throw new IllegalArgumentException("cache.invalidLoadFactor"); //$NON-NLS-1$
}
/**
* Sets the maximum amount of space that the cache can store
*
* @param limit Number of units of cache space
*/
@Override
public void setSpaceLimit(int limit) {
if (limit < fSpaceLimit) {
makeSpace(fSpaceLimit - limit);
}
fSpaceLimit = limit;
}
/**
* Attempts to shrink the cache if it has overflown.
* Returns true if the cache shrinks to less than or equal to <code>fSpaceLimit</code>.
*/
public boolean shrink() {
if (fOverflow > 0)
return makeSpace(0);
return true;
}
/**
* Returns a String that represents the value of this object. This method
* is for debugging purposes only.
*/
@Override
public String toString() {
return
"OverflowingLRUCache " + this.fillingRatio() + "% full\n" + //$NON-NLS-1$ //$NON-NLS-2$
this.toStringContents();
}
/**
* Updates the timestamp for the given entry, ensuring that the queue is
* kept in correct order. The entry must exist.
*
* <p>This method will do nothing if timestamps have been disabled.
*/
@Override
protected void updateTimestamp(LRUCacheEntry<K, T> entry) {
if (fTimestampsOn) {
entry._fTimestamp = fTimestampCounter++;
if (fEntryQueue != entry) {
this.privateRemoveEntry(entry, true);
this.privateAddEntry(entry, true);
}
}
}
}