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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.*;
import java.nio.*;
import java.nio.channels.*;
import java.util.concurrent.*;
import java.util.stream.*;
import java.util.*;
/* A simple implementation aiming for readability.
* Features:
* * memory mapped file
* * read chunks in parallel
* * minimise allocation
* * no unsafe
*
* Timings on 4 core i7-7500U CPU @ 2.70GHz:
* average_baseline: 4m48s
* ianopolous: 36s
*/
public class CalculateAverage_ianopolous {
public static final int MAX_LINE_LENGTH = 107;
public static final int MAX_STATIONS = 10_000;
public static void main(String[] args) throws Exception {
File input = new File("./measurements.txt");
long filesize = input.length();
// keep chunk size between 256 MB and 1G (1 chunk for files < 256MB)
long chunkSize = Math.min(Math.max(filesize / 32, 256 * 1024 * 1024), 1024 * 1024 * 1024L);
int nChunks = (int) ((filesize + chunkSize - 1) / chunkSize);
ExecutorService pool = Executors.newVirtualThreadPerTaskExecutor();
List<Future<List<List<Stat>>>> allResults = IntStream.range(0, nChunks)
.mapToObj(i -> pool.submit(() -> parseStats(i * chunkSize, Math.min((i + 1) * chunkSize, filesize))))
.toList();
TreeMap<String, Stat> merged = allResults.stream()
.parallel()
.flatMap(f -> {
try {
return f.get().stream().filter(Objects::nonNull).flatMap(Collection::stream);
}
catch (Exception e) {
return Stream.empty();
}
})
.collect(Collectors.toMap(s -> s.name(), s -> s, (a, b) -> a.merge(b), TreeMap::new));
System.out.println(merged);
}
public static boolean matchingStationBytes(int start, int end, MappedByteBuffer buffer, Stat existing) {
for (int i = start; i < end; i++) {
if (existing.name[i - start] != buffer.get(i))
return false;
}
return true;
}
public static Stat parseStation(int start, int end, int hash, MappedByteBuffer buffer, List<List<Stat>> stations) {
int index = Math.floorMod(hash, MAX_STATIONS);
List<Stat> matches = stations.get(index);
if (matches == null) {
List<Stat> value = new ArrayList<>();
byte[] stationBuffer = new byte[end - start];
buffer.position(start);
buffer.get(stationBuffer);
Stat res = new Stat(stationBuffer);
value.add(res);
stations.set(index, value);
return res;
}
else {
for (int i = 0; i < matches.size(); i++) {
Stat s = matches.get(i);
if (matchingStationBytes(start, end, buffer, s))
return s;
}
byte[] stationBuffer = new byte[end - start];
buffer.position(start);
buffer.get(stationBuffer);
Stat res = new Stat(stationBuffer);
matches.add(res);
return res;
}
}
public static List<List<Stat>> parseStats(long startByte, long endByte) {
try {
RandomAccessFile file = new RandomAccessFile("./measurements.txt", "r");
long maxEnd = Math.min(file.length(), endByte + MAX_LINE_LENGTH);
long len = maxEnd - startByte;
if (len > Integer.MAX_VALUE)
throw new RuntimeException("Segment size must fit into an int");
int maxDone = (int) (endByte - startByte);
MappedByteBuffer buffer = file.getChannel().map(FileChannel.MapMode.READ_ONLY, startByte, len);
int done = 0;
// read first partial line
if (startByte > 0) {
for (int i = 0; i < MAX_LINE_LENGTH; i++) {
byte b = buffer.get(i);
if (b == '\n') {
done = i + 1;
break;
}
}
}
List<List<Stat>> stations = new ArrayList<>(MAX_STATIONS);
for (int i = 0; i < MAX_STATIONS; i++)
stations.add(null);
int lineStart = done;
int lineSplit = 0;
short temperature = 0;
int hash = 1;
boolean negative = false;
while (done < maxDone) {
Stat station = null;
for (int i = done; i < done + MAX_LINE_LENGTH && i < maxEnd; i++) {
byte b = buffer.get(i);
if (b == '\n') {
done = i + 1;
temperature = negative ? (short) -temperature : temperature;
station.add(temperature);
lineStart = done;
station = null;
hash = 1;
break;
}
else if (b == ';') {
lineSplit = i;
station = parseStation(lineStart, lineSplit, hash, buffer, stations);
temperature = 0;
negative = false;
}
else if (station == null) {
hash = 31 * hash + b;
}
else if (b == '-') {
negative = true;
}
else if (b != '.') {
temperature = (short) (temperature * 10 + (b - 0x30));
}
}
}
return stations;
}
catch (IOException e) {
throw new RuntimeException(e);
}
}
public static class Stat {
final byte[] name;
int count = 0;
short min = Short.MAX_VALUE, max = Short.MIN_VALUE;
long total = 0;
public Stat(byte[] name) {
this.name = name;
}
public void add(short value) {
if (value < min)
min = value;
if (value > max)
max = value;
total += value;
count++;
}
public Stat merge(Stat value) {
if (value.min < min)
min = value.min;
if (value.max > max)
max = value.max;
total += value.total;
count += value.count;
return this;
}
private static double round(double value) {
return Math.round(value) / 10.0;
}
public String name() {
return new String(name);
}
public String toString() {
return round((double) min) + "/" + round(((double) total) / count) + "/" + round((double) max);
}
}
}
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