TObjectHash.java
//CHECKSTYLE:OFF
///////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2001, Eric D. Friedman All Rights Reserved.
// Copyright (c) 2009, Rob Eden All Rights Reserved.
// Copyright (c) 2009, Jeff Randall All Rights Reserved.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
///////////////////////////////////////////////////////////////////////////////
package org.spf4j.stackmonitor;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import gnu.trove.procedure.TObjectProcedure;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
/**
* An open addressed hashing implementation for Object types.
* <p/>
* Created: Sun Nov 4 08:56:06 2001
*
* @author Eric D. Friedman
* @author Rob Eden
* @author Jeff Randall
* @version $Id: TObjectHash.java,v 1.1.2.6 2009/11/07 03:36:44 robeden Exp $
*/
@SuppressFBWarnings
abstract public class TObjectHash<T> extends THash {
@SuppressWarnings({"UnusedDeclaration"})
public static final long serialVersionUID = 1L;
/**
* the set of Objects
*/
protected transient Object[] _set;
public static final Object REMOVED = new Object(), FREE = new Object();
/**
* Creates a new <code>TObjectHash</code> instance with the
* default capacity and load factor.
*/
public TObjectHash() {
super();
}
/**
* Creates a new <code>TObjectHash</code> instance whose capacity
* is the next highest prime above <tt>initialCapacity + 1</tt>
* unless that value is already prime.
*
* @param initialCapacity an <code>int</code> value
*/
public TObjectHash(int initialCapacity) {
super(initialCapacity);
}
public int capacity() {
return _set.length;
}
protected void removeAt(int index) {
_set[index] = REMOVED;
super.removeAt(index);
}
/**
* initializes the Object set of this hash table.
*
* @param initialCapacity an <code>int</code> value
* @return an <code>int</code> value
*/
public int setUp(int initialCapacity) {
int capacity;
capacity = super.setUp(initialCapacity);
if (capacity == 0) {
_set = org.spf4j.base.Arrays.EMPTY_OBJ_ARRAY;
return 0;
} else {
_set = new Object[capacity];
}
Arrays.fill(_set, FREE);
return capacity;
}
/**
* Executes <tt>procedure</tt> for each element in the set.
*
* @param procedure a <code>TObjectProcedure</code> value
* @return false if the loop over the set terminated because
* the procedure returned false for some value.
*/
@SuppressWarnings({"unchecked"})
public boolean forEach(TObjectProcedure<? super T> procedure) {
Object[] set = _set;
for (int i = set.length; i-- > 0;) {
if (set[i] != FREE
&& set[i] != REMOVED
&& !procedure.execute((T) set[i])) {
return false;
}
}
return true;
}
/**
* Searches the set for <tt>obj</tt>
*
* @param obj an <code>Object</code> value
* @return a <code>boolean</code> value
*/
@SuppressWarnings({"unchecked"})
public boolean contains(Object obj) {
return index(obj) >= 0;
}
/**
* Locates the index of <tt>obj</tt>.
*
* @param obj an <code>Object</code> value
* @return the index of <tt>obj</tt> or -1 if it isn't in the set.
*/
protected int index(Object obj) {
if (obj == null)
return indexForNull();
if (_set.length == 0) {
return -1;
}
// From here on we know obj to be non-null
final int hash = hash(obj) & 0x7fffffff;
int index = hash % _set.length;
Object cur = _set[index];
if (cur == FREE) {
return -1;
}
if (cur == obj || equals(obj, cur)) {
return index;
}
return indexRehashed(obj, index, hash, cur);
}
/**
* Locates the index of non-null <tt>obj</tt>.
*
* @param obj target key, know to be non-null
* @param index we start from
* @param hash
* @param cur
* @return
*/
private int indexRehashed(Object obj, int index, int hash, Object cur) {
final Object[] set = _set;
final int length = set.length;
// NOTE: here it has to be REMOVED or FULL (some user-given value)
// see Knuth, p. 529
int probe = 1 + (hash % (length - 2));
final int loopIndex = index;
do {
index -= probe;
if (index < 0) {
index += length;
}
cur = set[index];
//
if (cur == FREE)
return -1;
//
if ((cur == obj || equals(obj, cur)))
return index;
} while (index != loopIndex);
return -1;
}
/**
* Locates the index <tt>null</tt>.
* <p/>
* null specific loop exploiting several properties to simplify the iteration logic
* - the null value hashes to 0 we so we can iterate from the beginning.
* - the probe value is 1 for this case
* - object identity can be used to match this case
* <p/>
* --> this result a simpler loop
*
* @return
*/
private int indexForNull() {
int index = 0;
for (Object o : _set) {
if (o == null)
return index;
if (o == FREE)
return -1;
index++;
}
return -1;
}
/**
* Alias introduced to avoid breaking the API. The new method name insertKey() reflects the
* changes made to the logic.
*
* @param obj
* @return
* @deprecated use {@link #insertKey} instead
*/
@Deprecated
protected int insertionIndex(T obj) {
return insertKey(obj);
}
/**
* Locates the index at which <tt>key</tt> can be inserted. if
* there is already a value equal()ing <tt>key</tt> in the set,
* returns that value's index as <tt>-index - 1</tt>.
* <p/>
* If a slot is found the value is inserted. When a FREE slot is used the consumeFreeSlot field is
* set to true. This field should be used in the method invoking insertKey() to pass to postInsertHook()
*
* @param key an <code>Object</code> value
* @return the index of a FREE slot at which key can be inserted
* or, if key is already stored in the hash, the negative value of
* that index, minus 1: -index -1.
*/
protected int insertKey(T key) {
if (key == null)
return insertKeyForNull();
final int hash = hash(key) & 0x7fffffff;
int index = hash % _set.length;
Object cur = _set[index];
if (cur == FREE) {
_set[index] = key; // insert value
return index; // empty, all done
}
if (cur == key || equals(key, cur)) {
return -index - 1; // already stored
}
return insertKeyRehash(key, index, hash, cur);
}
/**
* Looks for a slot using double hashing for a non-null key values and inserts the value
* in the slot
*
* @param key non-null key value
* @param index natural index
* @param hash
* @param cur value of first matched slot
* @return
*/
private int insertKeyRehash(T key, int index, int hash, Object cur) {
final Object[] set = _set;
final int length = set.length;
// already FULL or REMOVED, must probe
// compute the double hash
final int probe = 1 + (hash % (length - 2));
final int loopIndex = index;
int firstRemoved = -1;
/**
* Look until FREE slot or we start to loop
*/
do {
// Identify first removed slot
if (cur == REMOVED && firstRemoved == -1)
firstRemoved = index;
index -= probe;
if (index < 0) {
index += length;
}
cur = set[index];
// A FREE slot stops the search
if (cur == FREE) {
if (firstRemoved != -1) {
_set[firstRemoved] = key;
return firstRemoved;
} else {
_set[index] = key; // insert value
return index;
}
}
if (cur == key || equals(key, cur)) {
return -index - 1;
}
// Detect loop
} while (index != loopIndex);
// We inspected all reachable slots and did not find a FREE one
// If we found a REMOVED slot we return the first one found
if (firstRemoved != -1) {
_set[firstRemoved] = key;
return firstRemoved;
}
// Can a resizing strategy be found that resizes the set?
throw new IllegalStateException("No free or removed slots available. Key set full?!!");
}
/**
* Looks for a slot using double hashing for a null key value and inserts the value.
* <p/>
* null specific loop exploiting several properties to simplify the iteration logic
* - the null value hashes to 0 we so we can iterate from the beginning.
* - the probe value is 1 for this case
* - object identity can be used to match this case
*
* @return
*/
private int insertKeyForNull() {
int index = 0;
int firstRemoved = -1;
// Look for a slot containing the 'null' value as key
for (Object o : _set) {
// Locate first removed
if (o == REMOVED && firstRemoved == -1)
firstRemoved = index;
if (o == FREE) {
if (firstRemoved != -1) {
_set[firstRemoved] = null;
return firstRemoved;
} else {
_set[index] = null; // insert value
return index;
}
}
if (o == null) {
return -index - 1;
}
index++;
}
// We inspected all reachable slots and did not find a FREE one
// If we found a REMOVED slot we return the first one found
if (firstRemoved != -1) {
_set[firstRemoved] = null;
return firstRemoved;
}
// We scanned the entire key set and found nothing, is set full?
// Can a resizing strategy be found that resizes the set?
throw new IllegalStateException("Could not find insertion index for null key. Key set full!?!!");
}
/**
* Convenience methods for subclasses to use in throwing exceptions about
* badly behaved user objects employed as keys. We have to throw an
* IllegalArgumentException with a rather verbose message telling the
* user that they need to fix their object implementation to conform
* to the general contract for java.lang.Object.
*
*
* @param o1 the first of the equal elements with unequal hash codes.
* @param o2 the second of the equal elements with unequal hash codes.
* @throws IllegalArgumentException the whole point of this method.
*/
protected final void throwObjectContractViolation(Object o1, Object o2)
throws IllegalArgumentException {
throw buildObjectContractViolation(o1, o2, "");
}
/**
* Convenience methods for subclasses to use in throwing exceptions about
* badly behaved user objects employed as keys. We have to throw an
* IllegalArgumentException with a rather verbose message telling the
* user that they need to fix their object implementation to conform
* to the general contract for java.lang.Object.
*
*
* @param o1 the first of the equal elements with unequal hash codes.
* @param o2 the second of the equal elements with unequal hash codes.
* @param size
*@param oldSize
* @param oldKeys @throws IllegalArgumentException the whole point of this method.
*/
protected final void throwObjectContractViolation(Object o1, Object o2, int size, int oldSize, Object[] oldKeys)
throws IllegalArgumentException {
String extra = dumpExtraInfo(o1, o2, size(), oldSize, oldKeys);
throw buildObjectContractViolation(o1, o2, extra);
}
/**
* Convenience methods for subclasses to use in throwing exceptions about
* badly behaved user objects employed as keys. We have to throw an
* IllegalArgumentException with a rather verbose message telling the
* user that they need to fix their object implementation to conform
* to the general contract for java.lang.Object.
*
*
* @param o1 the first of the equal elements with unequal hash codes.
* @param o2 the second of the equal elements with unequal hash codes.
* @throws IllegalArgumentException the whole point of this method.
*/
protected final IllegalArgumentException buildObjectContractViolation(Object o1, Object o2, String extra ) {
return new IllegalArgumentException("Equal objects must have equal hashcodes. " +
"During rehashing, Trove discovered that the following two objects claim " +
"to be equal (as in java.lang.Object.equals()) but their hashCodes (or " +
"those calculated by your TObjectHashingStrategy) are not equal." +
"This violates the general contract of java.lang.Object.hashCode(). See " +
"bullet point two in that method's documentation. object #1 =" + objectInfo(o1) +
"; object #2 =" + objectInfo(o2) + "\n" + extra);
}
protected boolean equals(Object notnull, Object two) {
if (two == null || two == REMOVED)
return false;
return notnull.equals(two);
}
protected int hash(Object notnull) {
return notnull.hashCode();
}
protected static String reportPotentialConcurrentMod(int newSize, int oldSize) {
// Note that we would not be able to detect concurrent paired of put()-remove()
// operations with this simple check
if (newSize != oldSize)
return "[Warning] apparent concurrent modification of the key set. " +
"Size before and after rehash() do not match " + oldSize + " vs " + newSize;
return "";
}
/**
*
* @param newVal the key being inserted
* @param oldVal the key already stored at that position
* @param currentSize size of the key set during rehashing
* @param oldSize size of the key set before rehashing
* @param oldKeys the old key set
*/
protected String dumpExtraInfo(Object newVal, Object oldVal, int currentSize, int oldSize, Object[] oldKeys) {
StringBuilder b = new StringBuilder();
//
b.append(dumpKeyTypes(newVal, oldVal));
b.append(reportPotentialConcurrentMod(currentSize, oldSize));
b.append(detectKeyLoss(oldKeys, oldSize));
// Is de same object already present? Double insert?
if (newVal == oldVal) {
b.append("Inserting same object twice, rehashing bug. Object= ").append(oldVal);
}
return b.toString();
}
/**
* Detect inconsistent hashCode() and/or equals() methods
*
* @param keys
* @param oldSize
* @return
*/
private static String detectKeyLoss(Object[] keys, int oldSize) {
StringBuilder buf = new StringBuilder();
Set<Object> k = makeKeySet(keys);
if (k.size() != oldSize) {
buf.append("\nhashCode() and/or equals() have inconsistent implementation");
buf.append("\nKey set lost entries, now got ").append(k.size()).append(" instead of ").append(oldSize);
buf.append(". This can manifest itself as an apparent duplicate key.");
}
return buf.toString();
}
private static Set<Object> makeKeySet(Object[] keys) {
Set<Object> types = new HashSet<Object>();
for (Object o : keys) {
if (o != FREE && o != REMOVED) {
types.add(o);
}
}
return types;
}
private static String equalsSymmetryInfo(Object a, Object b) {
StringBuilder buf = new StringBuilder();
if (a == b) {
return "a == b";
}
if (a.getClass() != b.getClass()) {
buf.append("Class of objects differ a=").append(a.getClass()).append(" vs b=").append(b.getClass());
boolean aEb = a.equals(b);
boolean bEa = b.equals(a);
if (aEb != bEa) {
buf.append("\nequals() of a or b object are asymmetric");
buf.append("\na.equals(b) =").append(aEb);
buf.append("\nb.equals(a) =").append(bEa);
}
}
return buf.toString();
}
protected static String objectInfo(Object o) {
return (o == null ? "class null" : o.getClass()) + " id= " + System.identityHashCode(o)
+ " hashCode= " + (o == null ? 0 : o.hashCode()) + " toString= " + String.valueOf(o);
}
private String dumpKeyTypes(Object newVal, Object oldVal) {
StringBuilder buf = new StringBuilder();
Set<Class<?>> types = new HashSet<Class<?>>();
for (Object o : _set) {
if (o != FREE && o != REMOVED) {
if (o != null)
types.add(o.getClass());
else
types.add(null);
}
}
if (types.size() > 1) {
buf.append("\nMore than one type used for keys. Watch out for asymmetric equals(). " +
"Read about the 'Liskov substitution principle' and the implications for equals() in java.");
buf.append("\nKey types: ").append(types);
buf.append(equalsSymmetryInfo(newVal, oldVal));
}
return buf.toString();
}
@Override
public void writeExternal(ObjectOutput out) throws IOException {
// VERSION
out.writeByte(0);
// SUPER
super.writeExternal(out);
}
@Override
public void readExternal(ObjectInput in)
throws IOException, ClassNotFoundException {
// VERSION
in.readByte();
// SUPER
super.readExternal(in);
}
} // TObjectHash