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/*
* Copyright 2023 The original authors
*
* 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 dev.morling.onebrc;
import java.io.File;
import java.io.IOException;
import java.lang.foreign.Arena;
import java.lang.reflect.Field;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.StandardOpenOption;
import java.util.Iterator;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.TreeMap;
import java.util.function.Function;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import sun.misc.Unsafe;
public class CalculateAverage_kuduwa_keshavram {
private static final String FILE = "./measurements.txt";
private static final Unsafe UNSAFE = initUnsafe();
private static Unsafe initUnsafe() {
try {
final Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
theUnsafe.setAccessible(true);
return (Unsafe) theUnsafe.get(Unsafe.class);
}
catch (NoSuchFieldException | IllegalAccessException e) {
throw new RuntimeException(e);
}
}
public static void main(String[] args) throws IOException, InterruptedException {
TreeMap<String, Measurement> resultMap = getFileSegments(new File(FILE))
.flatMap(
segment -> {
Result result = new Result();
while (segment.start < segment.end) {
byte[] city = new byte[100];
byte b;
int hash = 0;
int i = 0;
while ((b = UNSAFE.getByte(segment.start++)) != 59) {
hash = 31 * hash + b;
city[i++] = b;
}
byte[] newCity = new byte[i];
System.arraycopy(city, 0, newCity, 0, i);
int measurement = 0;
boolean negative = false;
while ((b = UNSAFE.getByte(segment.start++)) != 10) {
if (b == 45) {
negative = true;
}
else if (b == 46) {
// skip
}
else {
final int n = b - '0';
measurement = measurement * 10 + n;
}
}
putOrMerge(
result,
new Measurement(hash, newCity, negative ? measurement * -1 : measurement));
}
Iterator<Measurement> iterator = getMeasurementIterator(result);
return StreamSupport.stream(
Spliterators.spliteratorUnknownSize(iterator, Spliterator.NONNULL), true);
})
.collect(
Collectors.toMap(
measurement -> new String(measurement.city),
Function.identity(),
(m1, m2) -> {
m1.merge(m2);
return m1;
},
TreeMap::new));
System.out.println(resultMap);
}
private static Iterator<Measurement> getMeasurementIterator(Result result) {
return new Iterator<>() {
final int uniqueIndex = result.uniqueIndex;
final int[] indexArray = result.indexArray;
final Measurement[][] measurements = result.measurements;
int i = 0;
int j = 0;
@Override
public boolean hasNext() {
return i < uniqueIndex;
}
@Override
public Measurement next() {
Measurement measurement = measurements[indexArray[i]][j++];
if (measurements[indexArray[i]][j] == null) {
i++;
j = 0;
}
return measurement;
}
};
}
static class Result {
final Measurement[][] measurements = new Measurement[1024 * 128][3];
final int[] indexArray = new int[10_000];
int uniqueIndex = 0;
}
private static void putOrMerge(Result result, Measurement measurement) {
int index = measurement.hash & (result.measurements.length - 1);
Measurement[] existing = result.measurements[index];
for (int i = 0; i < existing.length; i++) {
Measurement existingMeasurement = existing[i];
if (existingMeasurement == null) {
result.measurements[index][i] = measurement;
if (i == 0) {
result.indexArray[result.uniqueIndex++] = index;
}
return;
}
if (equals(existingMeasurement.city, measurement.city)) {
existingMeasurement.merge(measurement);
return;
}
}
}
private static boolean equals(byte[] city1, byte[] city2) {
for (int i = 0; i < city1.length; i++) {
if (city1[i] != city2[i]) {
return false;
}
}
return true;
}
private static final class FileSegment {
long start;
long end;
private FileSegment(long start, long end) {
this.start = start;
this.end = end;
}
}
private static final class Measurement {
private final int hash;
private final byte[] city;
int min;
int max;
int sum;
int count;
private Measurement(int hash, byte[] city, int temp) {
this.hash = hash;
this.city = city;
this.min = this.max = this.sum = temp;
this.count = 1;
}
private void merge(Measurement m2) {
this.min = this.min < m2.min ? this.min : m2.min;
this.max = this.max > m2.max ? this.max : m2.max;
this.sum = this.sum + m2.sum;
this.count = this.count + m2.count;
}
@Override
public String toString() {
return String.format(
"%.1f/%.1f/%.1f", this.min / 10f, (this.sum / 10f) / this.count, this.max / 10f);
}
}
private static Stream<FileSegment> getFileSegments(final File file) throws IOException {
final int numberOfSegments = Runtime.getRuntime().availableProcessors() * 4;
final long[] chunks = new long[numberOfSegments + 1];
try (var fileChannel = FileChannel.open(file.toPath(), StandardOpenOption.READ)) {
final long fileSize = fileChannel.size();
final long segmentSize = (fileSize + numberOfSegments - 1) / numberOfSegments;
final long mappedAddress = fileChannel.map(MapMode.READ_ONLY, 0, fileSize, Arena.global()).address();
chunks[0] = mappedAddress;
final long endAddress = mappedAddress + fileSize;
for (int i = 1; i < numberOfSegments; ++i) {
long chunkAddress = mappedAddress + i * segmentSize;
// Align to first row start.
while (chunkAddress < endAddress && UNSAFE.getByte(chunkAddress++) != '\n') {
// nop
}
chunks[i] = Math.min(chunkAddress, endAddress);
}
chunks[numberOfSegments] = endAddress;
}
return IntStream.range(0, chunks.length - 1)
.mapToObj(chunkIndex -> new FileSegment(chunks[chunkIndex], chunks[chunkIndex + 1]))
.parallel();
}
}
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