org.apache.hadoop.hbase.regionserver.LruHashMap Maven / Gradle / Ivy
/**
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.hbase.regionserver;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.io.HeapSize;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.ClassSize;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* The LruHashMap is a memory-aware HashMap with a configurable maximum
* memory footprint.
*
* It maintains an ordered list of all entries in the/ map ordered by
* access time. When space needs to be freed becase the maximum has been
* reached, or the application has asked to free memory, entries will be
* evicted according to an LRU (least-recently-used) algorithm. That is,
* those entries which have not been accessed the longest will be evicted
* first.
*
* Both the Key and Value Objects used for this class must extend
* HeapSize in order to track heap usage.
*
* This class contains internal synchronization and is thread-safe.
*/
@InterfaceAudience.Private
public class LruHashMap
implements HeapSize, Map {
private static final Log LOG = LogFactory.getLog(LruHashMap.class);
/** The default size (in bytes) of the LRU */
private static final long DEFAULT_MAX_MEM_USAGE = 50000;
/** The default capacity of the hash table */
private static final int DEFAULT_INITIAL_CAPACITY = 16;
/** The maxmum capacity of the hash table */
private static final int MAXIMUM_CAPACITY = 1 << 30;
/** The default load factor to use */
private static final float DEFAULT_LOAD_FACTOR = 0.75f;
/** Memory overhead of this Object (for HeapSize) */
private static final int OVERHEAD = 5 * Bytes.SIZEOF_LONG +
2 * Bytes.SIZEOF_INT + 2 * Bytes.SIZEOF_FLOAT + 3 * ClassSize.REFERENCE +
1 * ClassSize.ARRAY;
/** Load factor allowed (usually 75%) */
private final float loadFactor;
/** Number of key/vals in the map */
private int size;
/** Size at which we grow hash */
private int threshold;
/** Entries in the map */
private Entry [] entries;
/** Pointer to least recently used entry */
private Entry headPtr;
/** Pointer to most recently used entry */
private Entry tailPtr;
/** Maximum memory usage of this map */
private long memTotal = 0;
/** Amount of available memory */
private long memFree = 0;
/** Number of successful (found) get() calls */
private long hitCount = 0;
/** Number of unsuccessful (not found) get() calls */
private long missCount = 0;
/**
* Constructs a new, empty map with the specified initial capacity,
* load factor, and maximum memory usage.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @param maxMemUsage the maximum total memory usage
* @throws IllegalArgumentException if the initial capacity is less than one
* @throws IllegalArgumentException if the initial capacity is greater than
* the maximum capacity
* @throws IllegalArgumentException if the load factor is <= 0
* @throws IllegalArgumentException if the max memory usage is too small
* to support the base overhead
*/
public LruHashMap(int initialCapacity, float loadFactor,
long maxMemUsage) {
if (initialCapacity < 1) {
throw new IllegalArgumentException("Initial capacity must be > 0");
}
if (initialCapacity > MAXIMUM_CAPACITY) {
throw new IllegalArgumentException("Initial capacity is too large");
}
if (loadFactor <= 0 || Float.isNaN(loadFactor)) {
throw new IllegalArgumentException("Load factor must be > 0");
}
if (maxMemUsage <= (OVERHEAD + initialCapacity * ClassSize.REFERENCE)) {
throw new IllegalArgumentException("Max memory usage too small to " +
"support base overhead");
}
/** Find a power of 2 >= initialCapacity */
int capacity = calculateCapacity(initialCapacity);
this.loadFactor = loadFactor;
this.threshold = calculateThreshold(capacity,loadFactor);
this.entries = new Entry[capacity];
this.memFree = maxMemUsage;
this.memTotal = maxMemUsage;
init();
}
/**
* Constructs a new, empty map with the specified initial capacity and
* load factor, and default maximum memory usage.
*
* @param initialCapacity the initial capacity
* @param loadFactor the load factor
* @throws IllegalArgumentException if the initial capacity is less than one
* @throws IllegalArgumentException if the initial capacity is greater than
* the maximum capacity
* @throws IllegalArgumentException if the load factor is <= 0
*/
public LruHashMap(int initialCapacity, float loadFactor) {
this(initialCapacity, loadFactor, DEFAULT_MAX_MEM_USAGE);
}
/**
* Constructs a new, empty map with the specified initial capacity and
* with the default load factor and maximum memory usage.
*
* @param initialCapacity the initial capacity
* @throws IllegalArgumentException if the initial capacity is less than one
* @throws IllegalArgumentException if the initial capacity is greater than
* the maximum capacity
*/
public LruHashMap(int initialCapacity) {
this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_MAX_MEM_USAGE);
}
/**
* Constructs a new, empty map with the specified maximum memory usage
* and with default initial capacity and load factor.
*
* @param maxMemUsage the maximum total memory usage
* @throws IllegalArgumentException if the max memory usage is too small
* to support the base overhead
*/
public LruHashMap(long maxMemUsage) {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR,
maxMemUsage);
}
/**
* Constructs a new, empty map with the default initial capacity,
* load factor and maximum memory usage.
*/
public LruHashMap() {
this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR,
DEFAULT_MAX_MEM_USAGE);
}
//--------------------------------------------------------------------------
/**
* Get the currently available memory for this LRU in bytes.
* This is (maxAllowed - currentlyUsed).
*
* @return currently available bytes
*/
public synchronized long getMemFree() {
return memFree;
}
/**
* Get the maximum memory allowed for this LRU in bytes.
*
* @return maximum allowed bytes
*/
public long getMemMax() {
return memTotal;
}
/**
* Get the currently used memory for this LRU in bytes.
*
* @return currently used memory in bytes
*/
public long getMemUsed() {
return (memTotal - getMemFree()); // FindBugs IS2_INCONSISTENT_SYNC
}
/**
* Get the number of hits to the map. This is the number of times
* a call to get() returns a matched key.
*
* @return number of hits
*/
public long getHitCount() {
return hitCount;
}
/**
* Get the number of misses to the map. This is the number of times
* a call to get() returns null.
*
* @return number of misses
*/
public synchronized long getMissCount() {
return missCount; // FindBugs IS2_INCONSISTENT_SYNC
}
/**
* Get the hit ratio. This is the number of hits divided by the
* total number of requests.
*
* @return hit ratio (double between 0 and 1)
*/
public double getHitRatio() {
return (double)((double)hitCount/
((double)(hitCount + getMissCount())));
}
/**
* Free the requested amount of memory from the LRU map.
*
* This will do LRU eviction from the map until at least as much
* memory as requested is freed. This does not affect the maximum
* memory usage parameter.
*
* @param requestedAmount memory to free from LRU in bytes
* @return actual amount of memory freed in bytes
*/
public synchronized long freeMemory(long requestedAmount) throws Exception {
if(requestedAmount > (getMemUsed() - getMinimumUsage())) {
return clearAll();
}
long freedMemory = 0;
while(freedMemory < requestedAmount) {
freedMemory += evictFromLru();
}
return freedMemory;
}
/**
* The total memory usage of this map
*
* @return memory usage of map in bytes
*/
public long heapSize() {
return (memTotal - getMemFree());
}
//--------------------------------------------------------------------------
/**
* Retrieves the value associated with the specified key.
*
* If an entry is found, it is updated in the LRU as the most recently
* used (last to be evicted) entry in the map.
*
* @param key the key
* @return the associated value, or null if none found
* @throws NullPointerException if key is null
*/
public synchronized V get(Object key) {
checkKey((K)key);
int hash = hash(key);
int i = hashIndex(hash, entries.length);
Entry e = entries[i];
while (true) {
if (e == null) {
missCount++;
return null;
}
if (e.hash == hash && isEqual(key, e.key)) {
// Hit! Update position in LRU
hitCount++;
updateLru(e);
return e.value;
}
e = e.next;
}
}
/**
* Insert a key-value mapping into the map.
*
* Entry will be inserted as the most recently used.
*
* Both the key and value are required to be Objects and must
* implement the HeapSize interface.
*
* @param key the key
* @param value the value
* @return the value that was previously mapped to this key, null if none
* @throws UnsupportedOperationException if either objects do not
* implement HeapSize
* @throws NullPointerException if the key or value is null
*/
public synchronized V put(K key, V value) {
checkKey(key);
checkValue(value);
int hash = hash(key);
int i = hashIndex(hash, entries.length);
// For old values
for (Entry e = entries[i]; e != null; e = e.next) {
if (e.hash == hash && isEqual(key, e.key)) {
V oldValue = e.value;
long memChange = e.replaceValue(value);
checkAndFreeMemory(memChange);
// If replacing an old value for this key, update in LRU
updateLru(e);
return oldValue;
}
}
long memChange = addEntry(hash, key, value, i);
checkAndFreeMemory(memChange);
return null;
}
/**
* Deletes the mapping for the specified key if it exists.
*
* @param key the key of the entry to be removed from the map
* @return the value associated with the specified key, or null
* if no mapping exists.
*/
public synchronized V remove(Object key) {
Entry e = removeEntryForKey((K)key);
if(e == null) return null;
// Add freed memory back to available
memFree += e.heapSize();
return e.value;
}
/**
* Gets the size (number of entries) of the map.
*
* @return size of the map
*/
public int size() {
return size;
}
/**
* Checks whether the map is currently empty.
*
* @return true if size of map is zero
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Clears all entries from the map.
*
* This frees all entries, tracking memory usage along the way.
* All references to entries are removed so they can be GC'd.
*/
public synchronized void clear() {
memFree += clearAll();
}
//--------------------------------------------------------------------------
/**
* Checks whether there is a value in the map for the specified key.
*
* Does not affect the LRU.
*
* @param key the key to check
* @return true if the map contains a value for this key, false if not
* @throws NullPointerException if the key is null
*/
public synchronized boolean containsKey(Object key) {
checkKey((K)key);
int hash = hash(key);
int i = hashIndex(hash, entries.length);
Entry e = entries[i];
while (e != null) {
if (e.hash == hash && isEqual(key, e.key))
return true;
e = e.next;
}
return false;
}
/**
* Checks whether this is a mapping which contains the specified value.
*
* Does not affect the LRU. This is an inefficient operation.
*
* @param value the value to check
* @return true if the map contains an entry for this value, false
* if not
* @throws NullPointerException if the value is null
*/
public synchronized boolean containsValue(Object value) {
checkValue((V)value);
Entry[] tab = entries;
for (int i = 0; i < tab.length ; i++)
for (Entry e = tab[i] ; e != null ; e = e.next)
if (value.equals(e.value))
return true;
return false;
}
//--------------------------------------------------------------------------
/**
* Enforces key constraints. Null keys are not permitted and key must
* implement HeapSize. It should not be necessary to verify the second
* constraint because that's enforced on instantiation?
*
* Can add other constraints in the future.
*
* @param key the key
* @throws NullPointerException if the key is null
* @throws UnsupportedOperationException if the key class does not
* implement the HeapSize interface
*/
private void checkKey(K key) {
if(key == null) {
throw new NullPointerException("null keys are not allowed");
}
}
/**
* Enforces value constraints. Null values are not permitted and value must
* implement HeapSize. It should not be necessary to verify the second
* constraint because that's enforced on instantiation?
*
* Can add other contraints in the future.
*
* @param value the value
* @throws NullPointerException if the value is null
* @throws UnsupportedOperationException if the value class does not
* implement the HeapSize interface
*/
private void checkValue(V value) {
if(value == null) {
throw new NullPointerException("null values are not allowed");
}
}
/**
* Returns the minimum memory usage of the base map structure.
*
* @return baseline memory overhead of object in bytes
*/
private long getMinimumUsage() {
return OVERHEAD + (entries.length * ClassSize.REFERENCE);
}
//--------------------------------------------------------------------------
/**
* Evicts and frees based on LRU until at least as much memory as requested
* is available.
*
* @param memNeeded the amount of memory needed in bytes
*/
private void checkAndFreeMemory(long memNeeded) {
while(memFree < memNeeded) {
evictFromLru();
}
memFree -= memNeeded;
}
/**
* Evicts based on LRU. This removes all references and updates available
* memory.
*
* @return amount of memory freed in bytes
*/
private long evictFromLru() {
long freed = headPtr.heapSize();
memFree += freed;
removeEntry(headPtr);
return freed;
}
/**
* Moves the specified entry to the most recently used slot of the
* LRU. This is called whenever an entry is fetched.
*
* @param e entry that was accessed
*/
private void updateLru(Entry e) {
Entry prev = e.getPrevPtr();
Entry next = e.getNextPtr();
if(next != null) {
if(prev != null) {
prev.setNextPtr(next);
next.setPrevPtr(prev);
} else {
headPtr = next;
headPtr.setPrevPtr(null);
}
e.setNextPtr(null);
e.setPrevPtr(tailPtr);
tailPtr.setNextPtr(e);
tailPtr = e;
}
}
/**
* Removes the specified entry from the map and LRU structure.
*
* @param entry entry to be removed
*/
private void removeEntry(Entry entry) {
K k = entry.key;
int hash = entry.hash;
int i = hashIndex(hash, entries.length);
Entry prev = entries[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (e.hash == hash && isEqual(k, e.key)) {
size--;
if (prev == e) {
entries[i] = next;
} else {
prev.next = next;
}
Entry prevPtr = e.getPrevPtr();
Entry nextPtr = e.getNextPtr();
if(prevPtr != null && nextPtr != null) {
prevPtr.setNextPtr(nextPtr);
nextPtr.setPrevPtr(prevPtr);
} else if(prevPtr != null) {
tailPtr = prevPtr;
prevPtr.setNextPtr(null);
} else if(nextPtr != null) {
headPtr = nextPtr;
nextPtr.setPrevPtr(null);
}
return;
}
prev = e;
e = next;
}
}
/**
* Removes and returns the entry associated with the specified
* key.
*
* @param key key of the entry to be deleted
* @return entry that was removed, or null if none found
*/
private Entry removeEntryForKey(K key) {
int hash = hash(key);
int i = hashIndex(hash, entries.length);
Entry prev = entries[i];
Entry e = prev;
while (e != null) {
Entry next = e.next;
if (e.hash == hash && isEqual(key, e.key)) {
size--;
if (prev == e) {
entries[i] = next;
} else {
prev.next = next;
}
// Updating LRU
Entry prevPtr = e.getPrevPtr();
Entry nextPtr = e.getNextPtr();
if(prevPtr != null && nextPtr != null) {
prevPtr.setNextPtr(nextPtr);
nextPtr.setPrevPtr(prevPtr);
} else if(prevPtr != null) {
tailPtr = prevPtr;
prevPtr.setNextPtr(null);
} else if(nextPtr != null) {
headPtr = nextPtr;
nextPtr.setPrevPtr(null);
}
return e;
}
prev = e;
e = next;
}
return e;
}
/**
* Adds a new entry with the specified key, value, hash code, and
* bucket index to the map.
*
* Also puts it in the bottom (most-recent) slot of the list and
* checks to see if we need to grow the array.
*
* @param hash hash value of key
* @param key the key
* @param value the value
* @param bucketIndex index into hash array to store this entry
* @return the amount of heap size used to store the new entry
*/
private long addEntry(int hash, K key, V value, int bucketIndex) {
Entry e = entries[bucketIndex];
Entry newE = new Entry(hash, key, value, e, tailPtr);
entries[bucketIndex] = newE;
// add as most recently used in lru
if (size == 0) {
headPtr = newE;
tailPtr = newE;
} else {
newE.setPrevPtr(tailPtr);
tailPtr.setNextPtr(newE);
tailPtr = newE;
}
// Grow table if we are past the threshold now
if (size++ >= threshold) {
growTable(2 * entries.length);
}
return newE.heapSize();
}
/**
* Clears all the entries in the map. Tracks the amount of memory being
* freed along the way and returns the total.
*
* Cleans up all references to allow old entries to be GC'd.
*
* @return total memory freed in bytes
*/
private long clearAll() {
Entry cur;
long freedMemory = 0;
for(int i=0; i entry = oldTable[i];
if(entry != null) {
// Set to null for GC
oldTable[i] = null;
do {
Entry next = entry.next;
int idx = hashIndex(entry.hash, newCapacity);
entry.next = newTable[idx];
newTable[idx] = entry;
entry = next;
} while(entry != null);
}
}
entries = newTable;
threshold = (int)(newCapacity * loadFactor);
}
/**
* Gets the hash code for the specified key.
* This implementation uses the additional hashing routine
* from JDK 1.4.
*
* @param key the key to get a hash value for
* @return the hash value
*/
private int hash(Object key) {
int h = key.hashCode();
h += ~(h << 9);
h ^= (h >>> 14);
h += (h << 4);
h ^= (h >>> 10);
return h;
}
/**
* Compares two objects for equality. Method uses equals method and
* assumes neither value is null.
*
* @param x the first value
* @param y the second value
* @return true if equal
*/
private boolean isEqual(Object x, Object y) {
return (x == y || x.equals(y));
}
/**
* Determines the index into the current hash table for the specified
* hashValue.
*
* @param hashValue the hash value
* @param length the current number of hash buckets
* @return the index of the current hash array to use
*/
private int hashIndex(int hashValue, int length) {
return hashValue & (length - 1);
}
/**
* Calculates the capacity of the array backing the hash
* by normalizing capacity to a power of 2 and enforcing
* capacity limits.
*
* @param proposedCapacity the proposed capacity
* @return the normalized capacity
*/
private int calculateCapacity(int proposedCapacity) {
int newCapacity = 1;
if(proposedCapacity > MAXIMUM_CAPACITY) {
newCapacity = MAXIMUM_CAPACITY;
} else {
while(newCapacity < proposedCapacity) {
newCapacity <<= 1;
}
if(newCapacity > MAXIMUM_CAPACITY) {
newCapacity = MAXIMUM_CAPACITY;
}
}
return newCapacity;
}
/**
* Calculates the threshold of the map given the capacity and load
* factor. Once the number of entries in the map grows to the
* threshold we will double the size of the array.
*
* @param capacity the size of the array
* @param factor the load factor of the hash
*/
private int calculateThreshold(int capacity, float factor) {
return (int)(capacity * factor);
}
/**
* Set the initial heap usage of this class. Includes class variable
* overhead and the entry array.
*/
private void init() {
memFree -= OVERHEAD;
memFree -= (entries.length * ClassSize.REFERENCE);
}
//--------------------------------------------------------------------------
/**
* Debugging function that returns a List sorted by access time.
*
* The order is oldest to newest (first in list is next to be evicted).
*
* @return Sorted list of entries
*/
public List> entryLruList() {
List> entryList = new ArrayList>();
Entry entry = headPtr;
while(entry != null) {
entryList.add(entry);
entry = entry.getNextPtr();
}
return entryList;
}
/**
* Debugging function that returns a Set of all entries in the hash table.
*
* @return Set of entries in hash
*/
@edu.umd.cs.findbugs.annotations.SuppressWarnings(value="IS2_INCONSISTENT_SYNC",
justification="Unused debugging function that reads only")
public Set> entryTableSet() {
Set> entrySet = new HashSet>();
Entry [] table = entries; // FindBugs IS2_INCONSISTENT_SYNC
for(int i=0;i> entrySet() {
throw new UnsupportedOperationException(
"entrySet() is intentionally unimplemented");
}
/**
* Intentionally unimplemented.
*/
public boolean equals(Object o) {
throw new UnsupportedOperationException(
"equals(Object) is intentionally unimplemented");
}
/**
* Intentionally unimplemented.
*/
public int hashCode() {
throw new UnsupportedOperationException(
"hashCode(Object) is intentionally unimplemented");
}
/**
* Intentionally unimplemented.
*/
public Set keySet() {
throw new UnsupportedOperationException(
"keySet() is intentionally unimplemented");
}
/**
* Intentionally unimplemented.
*/
public void putAll(Map m) {
throw new UnsupportedOperationException(
"putAll() is intentionally unimplemented");
}
/**
* Intentionally unimplemented.
*/
public Collection values() {
throw new UnsupportedOperationException(
"values() is intentionally unimplemented");
}
//--------------------------------------------------------------------------
/**
* Entry to store key/value mappings.
*
* Contains previous and next pointers for the doubly linked-list which is
* used for LRU eviction.
*
* Instantiations of this class are memory aware. Both the key and value
* classes used must also implement HeapSize.
*/
protected static class Entry
implements Map.Entry, HeapSize {
/** The baseline overhead memory usage of this class */
static final int OVERHEAD = 1 * Bytes.SIZEOF_LONG +
5 * ClassSize.REFERENCE + 2 * Bytes.SIZEOF_INT;
/** The key */
protected final K key;
/** The value */
protected V value;
/** The hash value for this entries key */
protected final int hash;
/** The next entry in the hash chain (for collisions) */
protected Entry next;
/** The previous entry in the LRU list (towards LRU) */
protected Entry prevPtr;
/** The next entry in the LRU list (towards MRU) */
protected Entry nextPtr;
/** The precomputed heap size of this entry */
protected long heapSize;
/**
* Create a new entry.
*
* @param h the hash value of the key
* @param k the key
* @param v the value
* @param nextChainPtr the next entry in the hash chain, null if none
* @param prevLruPtr the previous entry in the LRU
*/
Entry(int h, K k, V v, Entry nextChainPtr, Entry prevLruPtr) {
value = v;
next = nextChainPtr;
key = k;
hash = h;
prevPtr = prevLruPtr;
nextPtr = null;
// Pre-compute heap size
heapSize = OVERHEAD + k.heapSize() + v.heapSize();
}
/**
* Get the key of this entry.
*
* @return the key associated with this entry
*/
public K getKey() {
return key;
}
/**
* Get the value of this entry.
*
* @return the value currently associated with this entry
*/
public V getValue() {
return value;
}
/**
* Set the value of this entry.
*
* It is not recommended to use this method when changing the value.
* Rather, using replaceValue will return the difference
* in heap usage between the previous and current values.
*
* @param newValue the new value to associate with this entry
* @return the value previously associated with this entry
*/
public V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
/**
* Replace the value of this entry.
*
* Computes and returns the difference in heap size when changing
* the value associated with this entry.
*
* @param newValue the new value to associate with this entry
* @return the change in heap usage of this entry in bytes
*/
protected long replaceValue(V newValue) {
long sizeDiff = newValue.heapSize() - value.heapSize();
value = newValue;
heapSize += sizeDiff;
return sizeDiff;
}
/**
* Returns true is the specified entry has the same key and the
* same value as this entry.
*
* @param o entry to test against current
* @return true is entries have equal key and value, false if no
*/
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
Object k1 = getKey();
Object k2 = e.getKey();
if (k1 == k2 || (k1 != null && k1.equals(k2))) {
Object v1 = getValue();
Object v2 = e.getValue();
if (v1 == v2 || (v1 != null && v1.equals(v2)))
return true;
}
return false;
}
/**
* Returns the hash code of the entry by xor'ing the hash values
* of the key and value of this entry.
*
* @return hash value of this entry
*/
public int hashCode() {
return (key.hashCode() ^ value.hashCode());
}
/**
* Returns String representation of the entry in form "key=value"
*
* @return string value of entry
*/
public String toString() {
return getKey() + "=" + getValue();
}
//------------------------------------------------------------------------
/**
* Sets the previous pointer for the entry in the LRU.
* @param prevPtr previous entry
*/
protected void setPrevPtr(Entry prevPtr){
this.prevPtr = prevPtr;
}
/**
* Returns the previous pointer for the entry in the LRU.
* @return previous entry
*/
protected Entry getPrevPtr(){
return prevPtr;
}
/**
* Sets the next pointer for the entry in the LRU.
* @param nextPtr next entry
*/
protected void setNextPtr(Entry nextPtr){
this.nextPtr = nextPtr;
}
/**
* Returns the next pointer for the entry in teh LRU.
* @return next entry
*/
protected Entry getNextPtr(){
return nextPtr;
}
/**
* Returns the pre-computed and "deep" size of the Entry
* @return size of the entry in bytes
*/
public long heapSize() {
return heapSize;
}
}
}