/*******************************************************************************
* Copyright (c) 2002 - 2006 IBM Corporation.
* 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:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package com.ibm.wala.util.intset;
import java.lang.ref.WeakReference;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import com.ibm.wala.util.collections.HashMapFactory;
/**
* A repository for shared bit vectors as described by Heintze
*/
public class BitVectorRepository {
private final static boolean STATS = false;
private final static int STATS_WINDOW = 100;
private static int queries = 0;
private static int hits = 0;
private final static int SUBSET_DELTA = 5;
final private static Map<Integer, LinkedList<WeakReference<BitVectorIntSet>>> buckets = HashMapFactory.make();
/**
* @param value
* @return the BitVector in this repository which is the canonical shared
* subset representative of value; the result will have the same bits
* as value, except it may exclude up to SUBSET_DELTA bits.
* @throws IllegalArgumentException if value is null
*/
public static synchronized BitVectorIntSet findOrCreateSharedSubset(BitVectorIntSet value) {
if (value == null) {
throw new IllegalArgumentException("value is null");
}
if (STATS) {
queries++;
if (queries % STATS_WINDOW == 0) {
reportStats();
}
}
int size = value.size();
for (int i = size; i > size - SUBSET_DELTA; i--) {
LinkedList<WeakReference<BitVectorIntSet>> m = buckets.get(Integer.valueOf(i));
if (m != null) {
Iterator<WeakReference<BitVectorIntSet>> it = m.iterator();
while (it.hasNext()) {
WeakReference<BitVectorIntSet> wr = it.next();
BitVectorIntSet bv = wr.get();
if (bv != null) {
if (bv.isSubset(value)) {
// FOUND ONE!
if (STATS) {
hits++;
}
return bv;
}
} else {
// remove the weak reference to avoid leaks
it.remove();
}
}
}
}
// didn't find one. create one.
LinkedList<WeakReference<BitVectorIntSet>> m = buckets.get(size);
if (m == null) {
m = new LinkedList<WeakReference<BitVectorIntSet>>();
buckets.put(size, m);
}
BitVectorIntSet bv = new BitVectorIntSet(value);
m.add(new WeakReference<BitVectorIntSet>(bv));
return bv;
}
/**
*
*/
private static void reportStats() {
double percent = 100.0 * hits / queries;
System.err.println(("BitVectorRepository: queries " + queries + " hits " + percent));
System.err.println((" entries " + countEntries()));
}
/**
*/
private static int countEntries() {
int result = 0;
for (LinkedList<WeakReference<BitVectorIntSet>> l : buckets.values()) {
// don't worry about cleared WeakReferences; count will be rough
result += l.size();
}
return result;
}
}