| /******************************************************************************* |
| * Copyright (c) 2000, 2016 IBM Corporation and others. |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Public License v. 2.0 which is available at |
| * http://www.eclipse.org/legal/epl-2.0. |
| * |
| * SPDX-License-Identifier: EPL-2.0 |
| * |
| *******************************************************************************/ |
| package org.eclipse.dltk.internal.core.util; |
| |
| import java.text.NumberFormat; |
| import java.util.Enumeration; |
| import java.util.Hashtable; |
| |
| /** |
| * The <code>LRUCache</code> is a hashtable that stores a finite number of elements. |
| * When an attempt is made to add values to a full cache, the least recently used values |
| * in the cache are discarded to make room for the new values as necessary. |
| * |
| * <p>The data structure is based on the LRU virtual memory paging scheme. |
| * |
| * <p>Objects can take up a variable amount of cache space by implementing |
| * the <code>ILRUCacheable</code> interface. |
| * |
| * <p>This implementation is NOT thread-safe. Synchronization wrappers would |
| * have to be added to ensure atomic insertions and deletions from the cache. |
| * |
| */ |
| public class LRUCache implements Cloneable { |
| |
| /** |
| * This type is used internally by the LRUCache to represent entries |
| * stored in the cache. |
| * It is static because it does not require a pointer to the cache |
| * which contains it. |
| * |
| * @see LRUCache |
| */ |
| protected static class LRUCacheEntry { |
| |
| /** |
| * Hash table key |
| */ |
| public Object _fKey; |
| |
| /** |
| * Hash table value (an LRUCacheEntry object) |
| */ |
| public Object _fValue; |
| |
| /** |
| * Time value for queue sorting |
| */ |
| public int _fTimestamp; |
| |
| /** |
| * Cache footprint of this entry |
| */ |
| public int _fSpace; |
| |
| /** |
| * Previous entry in queue |
| */ |
| public LRUCacheEntry _fPrevious; |
| |
| /** |
| * Next entry in queue |
| */ |
| public LRUCacheEntry _fNext; |
| |
| /** |
| * Creates a new instance of the receiver with the provided values |
| * for key, value, and space. |
| */ |
| public LRUCacheEntry (Object key, Object value, int space) { |
| _fKey = key; |
| _fValue = value; |
| _fSpace = space; |
| } |
| |
| /** |
| * Returns a String that represents the value of this object. |
| */ |
| @Override |
| public String toString() { |
| |
| return "LRUCacheEntry [" + _fKey + "-->" + _fValue + "]"; //$NON-NLS-3$ //$NON-NLS-1$ //$NON-NLS-2$ |
| } |
| } |
| |
| /** |
| * Amount of cache space used so far |
| */ |
| protected int fCurrentSpace; |
| |
| /** |
| * Maximum space allowed in cache |
| */ |
| protected int fSpaceLimit; |
| |
| /** |
| * Counter for handing out sequential timestamps |
| */ |
| protected int fTimestampCounter; |
| |
| /** |
| * Hash table for fast random access to cache entries |
| */ |
| protected Hashtable fEntryTable; |
| |
| /** |
| * Start of queue (most recently used entry) |
| */ |
| protected LRUCacheEntry fEntryQueue; |
| |
| /** |
| * End of queue (least recently used entry) |
| */ |
| protected LRUCacheEntry fEntryQueueTail; |
| |
| /** |
| * Default amount of space in the cache |
| */ |
| protected static final int DEFAULT_SPACELIMIT = 100; |
| /** |
| * Creates a new cache. Size of cache is defined by |
| * <code>DEFAULT_SPACELIMIT</code>. |
| */ |
| public LRUCache() { |
| |
| this(DEFAULT_SPACELIMIT); |
| } |
| /** |
| * Creates a new cache. |
| * @param size Size of Cache |
| */ |
| public LRUCache(int size) { |
| |
| fTimestampCounter = fCurrentSpace = 0; |
| fEntryQueue = fEntryQueueTail = null; |
| fEntryTable = new Hashtable(size); |
| fSpaceLimit = size; |
| } |
| /** |
| * Returns a new cache containing the same contents. |
| * |
| * @return New copy of object. |
| */ |
| @Override |
| public Object clone() { |
| |
| LRUCache newCache = newInstance(fSpaceLimit); |
| LRUCacheEntry 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; |
| } |
| public double fillingRatio() { |
| return (fCurrentSpace) * 100.0 / fSpaceLimit; |
| } |
| /** |
| * Flushes all entries from the cache. |
| */ |
| public void flush() { |
| |
| fCurrentSpace = 0; |
| LRUCacheEntry entry = fEntryQueueTail; // Remember last entry |
| fEntryTable = new Hashtable(); // Clear it out |
| fEntryQueue = fEntryQueueTail = null; |
| while (entry != null) { // send deletion notifications in LRU order |
| privateNotifyDeletionFromCache(entry); |
| entry = entry._fPrevious; |
| } |
| } |
| /** |
| * Flushes the given entry from the cache. Does nothing if entry does not |
| * exist in cache. |
| * |
| * @param key Key of object to flush |
| */ |
| public void flush (Object key) { |
| |
| LRUCacheEntry entry; |
| |
| entry = (LRUCacheEntry) fEntryTable.get(key); |
| |
| /* If entry does not exist, return */ |
| if (entry == null) return; |
| |
| this.privateRemoveEntry (entry, false); |
| } |
| /** |
| * Answers the value in the cache at the given key. |
| * If the value is not in the cache, returns null |
| * |
| * @param key Hash table key of object to retrieve |
| * @return Retreived object, or null if object does not exist |
| */ |
| public Object get(Object key) { |
| |
| LRUCacheEntry entry = (LRUCacheEntry) fEntryTable.get(key); |
| if (entry == null) { |
| return null; |
| } |
| |
| this.updateTimestamp (entry); |
| return entry._fValue; |
| } |
| /** |
| * Returns the amount of space that is current used in the cache. |
| */ |
| public int getCurrentSpace() { |
| return fCurrentSpace; |
| } |
| /** |
| * Returns the maximum amount of space available in the cache. |
| */ |
| public int getSpaceLimit() { |
| return fSpaceLimit; |
| } |
| /** |
| * Returns an Enumeration of the keys currently in the cache. |
| */ |
| public Enumeration keys() { |
| |
| return fEntryTable.keys(); |
| } |
| /** |
| * Returns an enumeration that iterates over all the keys and values |
| * currently in the cache. |
| */ |
| public ICacheEnumeration keysAndValues() { |
| return new ICacheEnumeration() { |
| |
| Enumeration fValues = fEntryTable.elements(); |
| LRUCacheEntry fEntry; |
| |
| @Override |
| public boolean hasMoreElements() { |
| return fValues.hasMoreElements(); |
| } |
| |
| @Override |
| public Object nextElement() { |
| fEntry = (LRUCacheEntry) fValues.nextElement(); |
| return fEntry._fKey; |
| } |
| |
| @Override |
| public Object getValue() { |
| if (fEntry == null) { |
| throw new java.util.NoSuchElementException(); |
| } |
| return fEntry._fValue; |
| } |
| }; |
| } |
| /** |
| * 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. |
| * |
| * @param space Amount of space to free up |
| */ |
| protected boolean makeSpace (int space) { |
| |
| int limit; |
| |
| limit = this.getSpaceLimit(); |
| |
| /* if space is already available */ |
| if (fCurrentSpace + space <= limit) { |
| return true; |
| } |
| |
| /* if entry is too big for cache */ |
| if (space > limit) { |
| return false; |
| } |
| |
| /* Free up space by removing oldest entries */ |
| while (fCurrentSpace + space > limit && fEntryQueueTail != null) { |
| this.privateRemoveEntry (fEntryQueueTail, false); |
| } |
| return true; |
| } |
| /** |
| * Returns a new LRUCache instance |
| */ |
| protected LRUCache newInstance(int size) { |
| return new LRUCache(size); |
| } |
| /** |
| * 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 Object peek(Object key) { |
| |
| LRUCacheEntry entry = (LRUCacheEntry) fEntryTable.get(key); |
| if (entry == null) { |
| return null; |
| } |
| return entry._fValue; |
| } |
| /** |
| * Adds an entry for the given key/value/space. |
| */ |
| protected void privateAdd (Object key, Object value, int space) { |
| |
| LRUCacheEntry entry; |
| |
| entry = new LRUCacheEntry(key, value, space); |
| this.privateAddEntry (entry, false); |
| } |
| /** |
| * Adds the given entry from the receiver. |
| * @param shuffle Indicates whether we are just shuffling the queue |
| * (in which case, the entry table is not modified). |
| */ |
| protected void privateAddEntry (LRUCacheEntry entry, boolean shuffle) { |
| |
| if (!shuffle) { |
| fEntryTable.put (entry._fKey, entry); |
| fCurrentSpace += entry._fSpace; |
| } |
| |
| entry._fTimestamp = fTimestampCounter++; |
| entry._fNext = this.fEntryQueue; |
| entry._fPrevious = null; |
| |
| if (fEntryQueue == null) { |
| /* this is the first and last entry */ |
| fEntryQueueTail = entry; |
| } else { |
| fEntryQueue._fPrevious = entry; |
| } |
| |
| fEntryQueue = entry; |
| } |
| /** |
| * An entry has been removed from the cache, for example because it has |
| * fallen off the bottom of the LRU queue. |
| * Subclasses could over-ride this to implement a persistent cache below the LRU cache. |
| */ |
| protected void privateNotifyDeletionFromCache(LRUCacheEntry entry) { |
| // Default is NOP. |
| } |
| /** |
| * Removes the entry from the entry queue. |
| * @param shuffle indicates whether we are just shuffling the queue |
| * (in which case, the entry table is not modified). |
| */ |
| protected void privateRemoveEntry (LRUCacheEntry entry, boolean shuffle) { |
| |
| LRUCacheEntry previous, next; |
| |
| previous = entry._fPrevious; |
| next = entry._fNext; |
| |
| if (!shuffle) { |
| fEntryTable.remove(entry._fKey); |
| fCurrentSpace -= entry._fSpace; |
| privateNotifyDeletionFromCache(entry); |
| } |
| |
| /* 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. |
| */ |
| public Object put(Object key, Object value) { |
| |
| int newSpace, oldSpace, newTotal; |
| LRUCacheEntry entry; |
| |
| /* Check whether there's an entry in the cache */ |
| newSpace = spaceFor(value); |
| entry = (LRUCacheEntry) 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 |
| */ |
| oldSpace = entry._fSpace; |
| newTotal = getCurrentSpace() - oldSpace + newSpace; |
| if (newTotal <= getSpaceLimit()) { |
| updateTimestamp (entry); |
| entry._fValue = value; |
| entry._fSpace = newSpace; |
| this.fCurrentSpace = newTotal; |
| return value; |
| } else { |
| privateRemoveEntry (entry, false); |
| } |
| } |
| if (makeSpace(newSpace)) { |
| 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 removeKey (Object key) { |
| |
| LRUCacheEntry entry = (LRUCacheEntry) fEntryTable.get(key); |
| if (entry == null) { |
| return null; |
| } |
| Object value = entry._fValue; |
| this.privateRemoveEntry (entry, false); |
| return value; |
| } |
| /** |
| * Sets the maximum amount of space that the cache can store |
| * |
| * @param limit Number of units of cache space |
| */ |
| public void setSpaceLimit(int limit) { |
| if (limit < fSpaceLimit) { |
| makeSpace(fSpaceLimit - limit); |
| } |
| fSpaceLimit = limit; |
| } |
| /** |
| * Returns the space taken by the given value. |
| */ |
| protected int spaceFor (Object value) { |
| |
| if (value instanceof ILRUCacheable) { |
| return ((ILRUCacheable) value).getCacheFootprint(); |
| } else { |
| return 1; |
| } |
| } |
| /** |
| * Returns a String that represents the value of this object. This method |
| * is for debugging purposes only. |
| */ |
| @Override |
| public String toString() { |
| return |
| toStringFillingRation("LRUCache") + //$NON-NLS-1$ |
| toStringContents(); |
| } |
| |
| /** |
| * Returns a String that represents the contents of this object. This method |
| * is for debugging purposes only. |
| */ |
| protected String toStringContents() { |
| StringBuffer result = new StringBuffer(); |
| int length = fEntryTable.size(); |
| Object[] unsortedKeys = new Object[length]; |
| String[] unsortedToStrings = new String[length]; |
| Enumeration e = this.keys(); |
| for (int i = 0; i < length; i++) { |
| Object key = e.nextElement(); |
| unsortedKeys[i] = key; |
| unsortedToStrings[i] = |
| (key instanceof org.eclipse.dltk.internal.core.ModelElement) ? |
| ((org.eclipse.dltk.internal.core.ModelElement)key).getElementName() : |
| key.toString(); |
| } |
| ToStringSorter sorter = new ToStringSorter(); |
| sorter.sort(unsortedKeys, unsortedToStrings); |
| for (int i = 0; i < length; i++) { |
| String toString = sorter.sortedStrings[i]; |
| Object value = this.get(sorter.sortedObjects[i]); |
| result.append(toString); |
| result.append(" -> "); //$NON-NLS-1$ |
| result.append(value); |
| result.append("\n"); //$NON-NLS-1$ |
| } |
| return result.toString(); |
| } |
| |
| public String toStringFillingRation(String cacheName) { |
| StringBuffer buffer = new StringBuffer(cacheName); |
| buffer.append('['); |
| buffer.append(getSpaceLimit()); |
| buffer.append("]: "); //$NON-NLS-1$ |
| buffer.append(NumberFormat.getInstance().format(fillingRatio())); |
| buffer.append("% full"); //$NON-NLS-1$ |
| return buffer.toString(); |
| } |
| |
| /** |
| * Updates the timestamp for the given entry, ensuring that the queue is |
| * kept in correct order. The entry must exist |
| */ |
| protected void updateTimestamp (LRUCacheEntry entry) { |
| |
| entry._fTimestamp = fTimestampCounter++; |
| if (fEntryQueue != entry) { |
| this.privateRemoveEntry (entry, true); |
| this.privateAddEntry (entry, true); |
| } |
| return; |
| } |
| } |