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PhIteratorNoGC.java
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PhIteratorNoGC.java
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/*
* Copyright 2011-2016 ETH Zurich. All Rights Reserved.
* Copyright 2016-2018 Tilmann Zäschke. All Rights Reserved.
* Copyright 2019 Improbable Worlds Limited. All rights reserved.
*
* This file is part of the PH-Tree project.
*
* 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 ch.ethz.globis.phtree.v16;
import java.util.NoSuchElementException;
import ch.ethz.globis.phtree.PhEntry;
import ch.ethz.globis.phtree.PhFilter;
import ch.ethz.globis.phtree.PhTree.PhQuery;
import ch.ethz.globis.phtree.PhTreeHelper;
import ch.ethz.globis.phtree.util.unsynced.LongArrayOps;
/**
* This PhIterator uses a loop instead of recursion in findNextElement();.
* It also reuses PhEntry objects to avoid unnecessary creation of objects.
* Calls to next() and nextKey() will result in creation of new PhEntry and long[] objects
* respectively to maintain expected behaviour. However, the nextEntryUnstable() method
* returns the internal PhEntry without creating any new objects. The returned PhEntry and long[]
* are valid until the next call to nextXXX().
*
* @author ztilmann
*
* @param <T> value type
*/
public final class PhIteratorNoGC<T> implements PhQuery<T> {
private class PhIteratorStack {
private final NodeIteratorNoGC<T>[] stack;
private int size = 0;
@SuppressWarnings("unchecked")
PhIteratorStack() {
stack = new NodeIteratorNoGC[PhTree16.DEPTH_64];
}
public boolean isEmpty() {
return size == 0;
}
public NodeIteratorNoGC<T> prepareAndPush(Node node, long[] prefix) {
NodeIteratorNoGC<T> ni = stack[size++];
if (ni == null) {
ni = new NodeIteratorNoGC<>(dims);
stack[size-1] = ni;
}
ni.init(rangeMin, rangeMax, node, checker, prefix);
return ni;
}
public NodeIteratorNoGC<T> peek() {
return stack[size-1];
}
public NodeIteratorNoGC<T> pop() {
return stack[--size];
}
}
private final int dims;
private final PhIteratorStack stack;
private long[] rangeMin;
private long[] rangeMax;
private PhFilter checker;
private final PhTree16<T> pht;
private PhEntry<T> resultFree;
private PhEntry<T> resultToReturn;
private boolean isFinished = false;
public PhIteratorNoGC(PhTree16<T> pht, PhFilter checker) {
this.dims = pht.getDim();
this.checker = checker;
this.stack = new PhIteratorStack();
this.pht = pht;
this.resultFree = new PhEntry<>(new long[dims], null);
this.resultToReturn = new PhEntry<>(new long[dims], null);
}
@Override
public PhIteratorNoGC<T> reset(long[] rangeMin, long[] rangeMax) {
this.rangeMin = rangeMin;
this.rangeMax = rangeMax;
this.stack.size = 0;
this.isFinished = false;
if (pht.getRoot() == null) {
//empty index
isFinished = true;
return this;
}
stack.prepareAndPush(pht.getRoot(), null);
findNextElement();
return this;
}
private void findNextElement() {
PhEntry<T> result = resultFree;
while (!stack.isEmpty()) {
NodeIteratorNoGC<T> p = stack.peek();
while (p.increment(result)) {
if (result.hasNodeInternal()) {
p = stack.prepareAndPush((Node) result.getNodeInternal(), result.getKey());
} else {
resultFree = resultToReturn;
resultToReturn = result;
return;
}
}
// no matching (more) elements found
stack.pop();
}
//finished
isFinished = true;
}
@Override
public long[] nextKey() {
long[] key = nextEntryReuse().getKey();
long[] ret = new long[key.length];
LongArrayOps.arraycopy(key, 0, ret, 0, key.length);
return ret;
}
@Override
public T nextValue() {
return nextEntryReuse().getValue();
}
@Override
public boolean hasNext() {
return !isFinished;
}
@Override
public PhEntry<T> nextEntry() {
return new PhEntry<>(nextEntryReuse());
}
@Override
public T next() {
T v = nextEntryReuse().getValue();
return v == PhTreeHelper.NULL ? null : v;
}
/**
* Special 'next' method that avoids creating new objects internally by reusing Entry objects.
* Advantage: Should completely avoid any GC effort.
* Disadvantage: Returned PhEntries are not stable and are only valid until the
* next call to next(). After that they may change state.
* @return The next entry
*/
@Override
public PhEntry<T> nextEntryReuse() {
if (isFinished) {
throw new NoSuchElementException();
}
PhEntry<T> ret = resultToReturn;
findNextElement();
return ret;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}