THash.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.impl.Constants;
import gnu.trove.impl.HashFunctions;
import gnu.trove.impl.PrimeFinder;
import java.io.Externalizable;
import java.io.ObjectOutput;
import java.io.IOException;
import java.io.ObjectInput;
/**
* Base class for hashtables that use open addressing to resolve
* collisions.
* removed compaction element to reduce memory footprint.
* use case for this implementation does not have removes.
*
* Created: Wed Nov 28 21:11:16 2001
*
* @author Eric D. Friedman
* @author Rob Eden (auto-compaction)
* @author Jeff Randall
* @author zfarkas
*
* @version $Id: THash.java,v 1.1.2.4 2010/03/02 00:55:34 robeden Exp $
*/
@SuppressFBWarnings
abstract public class THash implements Externalizable {
@SuppressWarnings( { "UnusedDeclaration" } )
static final long serialVersionUID = -1792948471915530295L;
/** the load above which rehashing occurs. */
protected static final float DEFAULT_LOAD_FACTOR = Float.parseFloat(System.getProperty("spf4j.methodMap.loadFactor",
"0.7"));
/**
* the default initial capacity for the hash table. This is one
* less than a prime value because one is added to it when
* searching for a prime capacity to account for the free slot
* required by open addressing. Thus, the real default capacity is
* 11.
*/
protected static final int DEFAULT_CAPACITY = Constants.DEFAULT_CAPACITY;
/** the current number of occupied slots in the hash. */
protected transient int _size;
/**
* The maximum number of elements allowed without allocating more
* space.
*/
protected int _maxSize;
/**
* Creates a new <code>THash</code> instance with the default
* capacity and load factor.
*/
public THash() {
this( DEFAULT_CAPACITY );
}
/**
* Creates a new <code>THash</code> instance with a prime capacity
* at or near the minimum needed to hold <tt>initialCapacity</tt>
* elements with load factor <tt>loadFactor</tt> without triggering
* a rehash.
*
* @param initialCapacity an <code>int</code> value
* @param loadFactor a <code>float</code> value
*/
public THash( int initialCapacity) {
super();
setUp( HashFunctions.fastCeil( initialCapacity / DEFAULT_LOAD_FACTOR ) );
}
/**
* Tells whether this set is currently holding any elements.
*
* @return a <code>boolean</code> value
*/
public boolean isEmpty() {
return 0 == _size;
}
/**
* Returns the number of distinct elements in this collection.
*
* @return an <code>int</code> value
*/
public int size() {
return _size;
}
/** @return the current physical capacity of the hash table. */
abstract public int capacity();
/**
* Ensure that this hashtable has sufficient capacity to hold
* <tt>desiredCapacity<tt> <b>additional</b> elements without
* requiring a rehash. This is a tuning method you can call
* before doing a large insert.
*
* @param desiredCapacity an <code>int</code> value
*/
public void ensureCapacity(int desiredCapacity) {
int requiredSize = desiredCapacity + _size;
if (requiredSize > _maxSize) {
rehash(PrimeFinder.nextPrime(Math.max( _size + (_size >> 1) + 1,
HashFunctions.fastCeil((requiredSize) / DEFAULT_LOAD_FACTOR ) + 1) ) );
computeMaxSize(capacity());
}
}
/**
* Delete the record at <tt>index</tt>. Reduces the size of the
* collection by one.
*
* @param index an <code>int</code> value
*/
protected void removeAt( int index ) {
_size--;
}
/** Empties the collection. */
public void clear() {
_size = 0;
}
/**
* initializes the hashtable to a prime capacity which is at least
* <tt>initialCapacity + 1</tt>.
*
* @param initialCapacity an <code>int</code> value
* @return the actual capacity chosen
*/
protected int setUp( int initialCapacity ) {
if (initialCapacity == 0) {
return 0;
}
int capacity;
capacity = PrimeFinder.nextPrime( initialCapacity );
computeMaxSize( capacity );
return capacity;
}
/**
* Rehashes the set.
*
* @param newCapacity an <code>int</code> value
*/
protected abstract void rehash( int newCapacity );
/**
* Computes the values of maxSize. There will always be at least
* one free slot required.
*
* @param capacity an <code>int</code> value
*/
protected void computeMaxSize( int capacity ) {
// need at least one free slot for open addressing
_maxSize = Math.min( capacity - 1, (int) ( capacity * DEFAULT_LOAD_FACTOR ) );
}
/**
* After an insert, this hook is called to adjust the size/free
* values of the set and to perform rehashing if necessary.
*
* @param usedFreeSlot the slot
*/
protected final void postInsertHook() {
++_size;
}
protected int calculateGrownCapacity() {
return capacity() << 1;
}
public void writeExternal( ObjectOutput out ) throws IOException {
// VERSION
out.writeByte( 0 );
}
public void readExternal( ObjectInput in )
throws IOException, ClassNotFoundException {
// VERSION
in.readByte();
setUp( (int) Math.ceil( DEFAULT_CAPACITY / DEFAULT_LOAD_FACTOR ) );
}
}// THash