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Xodus is pure Java transactional schema-less embedded database
/**
* Copyright 2010 - 2018 JetBrains s.r.o.
*
* 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 jetbrains.exodus.query;
import jetbrains.exodus.entitystore.Entity;
import org.jetbrains.annotations.NotNull;
import java.util.*;
public class InMemoryTimSortIterable extends SortEngine.InMemorySortIterable {
private static final int MIN_RUN_LENGTH = 32;
public InMemoryTimSortIterable(@NotNull final Iterable source, @NotNull final Comparator comparator) {
super(source, comparator);
}
@Override
public Iterator iterator() {
return new Iterator() {
private List src;
private int runCount;
private int nodeCount;
/**
* for leaves (runs) this is index of first element left
* in particular, after init this is the leftmost element of the run
* for other nodes from[] contains index of the minimal element calculated
* or -1 if it's not calculated yet
*/
private int[] from;
private int[] len;
private int[] left;
private int[] right;
private int current;
private int head;
@Override
public boolean hasNext() {
if (src == null) {
init();
}
return current < src.size();
}
@Override
public Entity next() {
if (src == null) {
init();
}
if (current >= src.size()) {
throw new NoSuchElementException();
}
computeMinimum();
int r = from[head];
markAsUsed(r);
current++;
return src.get(r);
}
private void computeMinimum() {
ArrayList stack = new ArrayList<>();
stack.add(head);
while (from[head] < 0) {
int node = stack.get(stack.size() - 1);
if (from[left[node]] < 0) {
stack.add(left[node]);
} else if (from[right[node]] < 0) {
stack.add(right[node]);
} else {
if (len[right[node]] <= 0 || (len[left[node]] > 0 && comparator.compare(src.get(from[left[node]]), src.get(from[right[node]])) <= 0)) {
from[node] = from[left[node]];
len[left[node]]--;
} else {
from[node] = from[right[node]];
len[right[node]]--;
}
stack.remove(stack.size() - 1);
}
}
}
private void markAsUsed(int r) {
int i = head;
while (left[i] >= 0) {
from[i] = -1;
if (from[left[i]] == r) {
i = left[i];
} else {
i = right[i];
}
}
from[i]++;
if (len[i] <= 0) {
from[i] = src.size();
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
public void init() {
src = new ArrayList<>();
for (final Entity entity : source) {
src.add(entity);
}
int n = src.size();
if (n == 0) {
return;
}
int minRunLength = n;
int b = 0;
while (minRunLength >= InMemoryTimSortIterable.MIN_RUN_LENGTH) {
b |= minRunLength;
minRunLength >>= 1;
}
minRunLength += b & 1;
int maxRuns = 1 + (n + minRunLength - 1) / minRunLength;
from = new int[maxRuns * 2 - 1];
len = new int[maxRuns * 2 - 1];
left = new int[maxRuns * 2 - 1];
Arrays.fill(left, -1);
right = new int[maxRuns * 2 - 1];
ArrayList stack = new ArrayList<>();
runCount = 0;
boolean growing = true;
for (int i = 1; i < n; i++) {
// on the run
if ((comparator.compare(src.get(i - 1), src.get(i)) <= 0) == growing) {
continue;
}
// start of run
if (i == from[runCount] + 1) {
growing = !(growing);
continue;
}
// reverse if needed
if (!(growing)) {
reverse(i);
}
// insert several next elements into run to achieve run length minRunLength
for (; i < n && i - from[runCount] < minRunLength; i++) {
Entity t = src.get(i);
int j = i - 1;
for (; j >= from[runCount] && comparator.compare(src.get(j), t) > 0; j--) {
src.set(j + 1, src.get(j));
}
src.set(j + 1, t);
}
len[runCount] = i - from[runCount];
from[++runCount] = i;
stack.add(runCount - 1);
// collapse
while (true) {
int s = stack.size();
if (s >= 3 && len[stack.get(s - 3)] <= len[stack.get(s - 2)] + len[stack.get(s - 1)]) {
if (len[stack.get(s - 3)] < len[stack.get(s - 1)]) {
unite(stack, s - 3, maxRuns);
} else {
unite(stack, s - 2, maxRuns);
}
} else if (s >= 2 && len[stack.get(s - 2)] <= len[stack.get(s - 1)]) {
unite(stack, s - 2, maxRuns);
} else {
break;
}
}
}
// last run
len[runCount] = n - from[runCount];
if (len[runCount] > 0) {
// reverse if needed
if (!(growing)) {
reverse(n);
}
stack.add(runCount);
runCount++;
}
// collapse remaining
for (int i = stack.size() - 2; i >= 0; i--) {
if (i > 0 && len[stack.get(i - 1)] < len[stack.get(i + 1)]) {
unite(stack, i - 1, maxRuns);
} else {
unite(stack, i, maxRuns);
}
}
// for inner nodes min value is unset
for (int i = 0; i < nodeCount; i++) {
from[i + maxRuns] = -1;
}
head = stack.get(0);
}
private void reverse(int to) {
for (int l = from[runCount], r = to - 1; l < r; l++, r--) {
Entity t = src.get(l);
src.set(l, src.get(r));
src.set(r, t);
}
}
/**
* replaces stack[p] and stack[p + 1] with a node pointing to them
* @param stack stack
* @param p p
* @param shift shift
*/
private void unite(ArrayList stack, int p, int shift) {
int node = nodeCount + shift;
from[node] = from[stack.get(p)];
len[node] = len[stack.get(p)] + len[stack.get(p + 1)];
left[node] = stack.get(p);
right[node] = stack.get(p + 1);
stack.set(p, node);
nodeCount++;
stack.remove(p + 1);
}
};
}
}