/**
Copyright (C) SYSTAP, LLC 2006-2012. All rights reserved.
Licensed 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 com.bigdata.rdf.graph.impl.frontier;
import java.util.Arrays;
import java.util.Iterator;
import org.openrdf.model.Value;
import com.bigdata.rdf.graph.IStaticFrontier;
import com.bigdata.rdf.graph.impl.util.IArraySlice;
import com.bigdata.rdf.graph.impl.util.IManagedArray;
import com.bigdata.rdf.graph.impl.util.ManagedArray;
/**
* An implementation of a "static" frontier that grows and reuses the backing
* vertex array.
* <p>
* Note: This implementation has package private methods that permit certain
* kinds of mutation.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
*/
public class StaticFrontier2 implements IStaticFrontier {
/**
* The backing structure.
*/
private final IManagedArray<Value> backing;
/**
* A slice onto the {@link #backing} structure for the current frontier.
* This gets replaced when the frontier is changed.
*/
private IArraySlice<Value> vertices;
private boolean compact = true;
public StaticFrontier2() {
/*
* The managed backing array.
*/
backing = new ManagedArray<Value>(Value.class);
/*
* Initialize with an empty slice. The backing [] will grow as
* necessary.
*/
vertices = backing.slice(0/* off */, 0/* len */);
}
@Override
public boolean isCompact() {
return compact;
}
public void setCompact(final boolean newValue) {
this.compact = newValue;
}
@Override
public int size() {
return vertices.len();
}
@Override
public boolean isEmpty() {
return vertices.len() == 0;
}
@Override
public Iterator<Value> iterator() {
return vertices.iterator();
}
/**
* Grow the backing array iff necessary. Regardless, the entries from end of
* the current view to the first non-<code>null</code> are cleared. This is
* done to faciltiate GC by clearing references that would otherwise remain
* if/when the frontier contracted.
*
* @param minCapacity
* The required minimum capacity.
*/
public void resetAndEnsureCapacity(final int minCapacity) {
final int len0 = size();
backing.ensureCapacity(minCapacity);
final int len1 = backing.len();
if (len1 > len0) {
final Value[] a = backing.array();
for (int i = len0; i < len1; i++) {
if (a[i] == null)
break;
a[i] = null;
}
}
/*
* Replace the view. The caller will need to copy the data into the
* backing array before it will appear in the new view.
*/
this.vertices = backing.slice(0/* off */, minCapacity/* len */);
}
/**
* Copy a slice into the backing array. This method is intended for use by
* parallel threads. The backing array MUST have sufficient capacity. The
* threads MUST write to offsets that are known to not overlap. NO checking
* is done to ensure that the concurrent copy of these slices will not
* overlap.
*
* @param off
* The offset at which to copy the slice.
* @param slice
* The slice.
*/
public void copyIntoResetFrontier(final int off,
final IArraySlice<Value> slice) {
backing.put(off/* dstoff */, slice.array()/* src */,
slice.off()/* srcoff */, slice.len()/* srclen */);
}
@Override
public void resetFrontier(final int minCapacity, final boolean sort,
final Iterator<Value> itr) {
copyScheduleIntoFrontier(minCapacity, itr);
if (sort) {
/*
* Sort the current slice of the backing array.
*/
Arrays.sort(backing.array(), 0/* fromIndex */, vertices.len()/* toIndex */);
}
}
/**
* Copy the data from the iterator into the backing array and update the
* slice which provides our exposed view of the backing array.
*
* @param minCapacity
* The minimum required capacity for the backing array.
* @param itr
* The source from which we will repopulate the backing array.
*/
private void copyScheduleIntoFrontier(final int minCapacity,
final Iterator<Value> itr) {
// ensure enough capacity for the new frontier.
backing.ensureCapacity(minCapacity);
// the actual backing array. should not changed since pre-extended.
final Value[] a = backing.array();
int nvertices = 0;
while (itr.hasNext()) {
final Value v = itr.next();
a[nvertices++] = v;
}
/*
* Null fill until the end of the last frontier. That will help out GC.
* Otherwise those IV references are pinned and can hang around. We
* could track the high water mark on the backing array for this
* purpose.
*/
for (int i = nvertices; i < a.length; i++) {
if (a[i] == null)
break;
a[i] = null;
}
/*
* Take a slice of the backing showing only the valid entries and use it
* to replace the view of the backing array.
*/
this.vertices = backing.slice(0/* off */, nvertices);
}
@Override
public String toString() {
return getClass().getName() + "{size=" + size() + ",compact="
+ isCompact() + ",capacity=" + backing.capacity() + "}";
}
}