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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.IOException;
import java.lang.foreign.Arena;
import java.lang.foreign.MemorySegment;
import java.nio.channels.FileChannel;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.TreeMap;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import static java.lang.Math.ceil;
import static java.lang.Math.max;
import static java.lang.Math.min;
import static java.lang.Runtime.getRuntime;
import static java.lang.foreign.ValueLayout.JAVA_BYTE;
import static java.nio.channels.FileChannel.MapMode.READ_ONLY;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.util.concurrent.CompletableFuture.supplyAsync;
public class CalculateAverage_anestoruk {
private static final String path = "./measurements.txt";
private static final int cpus = getRuntime().availableProcessors();
public static void main(String[] args) throws IOException {
List<SegmentRange> rangeList = new ArrayList<>();
MemorySegment segment;
try (FileChannel channel = FileChannel.open(Path.of(path))) {
final long fileSize = channel.size();
final long chunkSize = calculateChunkSize(fileSize);
final int chunks = (int) ceil((double) fileSize / chunkSize);
segment = channel.map(READ_ONLY, 0, fileSize, Arena.global());
long startOffset = 0;
long size = chunkSize;
for (int i = 0; i < chunks && size > 0; i++) {
long endOffset = startOffset + size;
while (endOffset < fileSize && segment.get(JAVA_BYTE, endOffset) != '\n') {
endOffset++;
}
rangeList.add(new SegmentRange(startOffset, endOffset));
startOffset = endOffset + 1;
size = min(chunkSize, fileSize - startOffset);
}
}
TreeMap<String, Record> result = new TreeMap<>();
try (ExecutorService executor = Executors.newFixedThreadPool(cpus)) {
List<CompletableFuture<Record[]>> futures = new ArrayList<>();
for (SegmentRange range : rangeList) {
futures.add(supplyAsync(() -> process(range, segment), executor));
}
for (CompletableFuture<Record[]> future : futures) {
try {
Record[] partialResult = future.get();
mergeResult(result, partialResult);
}
catch (InterruptedException | ExecutionException ex) {
throw new RuntimeException(ex);
}
}
}
System.out.println(result);
}
private static long calculateChunkSize(long fileSize) {
int divisor = cpus;
long chunkSize;
if (fileSize > 10_000) {
while ((chunkSize = fileSize / divisor) > Integer.MAX_VALUE - 512) {
divisor *= 2;
}
return chunkSize;
}
return fileSize;
}
private static Record[] process(SegmentRange range, MemorySegment segment) {
Record[] records = new Record[1024 * 100];
byte[] cityBuffer = new byte[100];
long offset = range.startOffset;
byte b;
while (offset < range.endOffset) {
int cityLength = 0;
int hash = 0;
while ((b = segment.get(JAVA_BYTE, offset++)) != ';') {
cityBuffer[cityLength++] = b;
hash = hash * 31 + b;
}
hash = Math.abs(hash);
int value = 0;
boolean negative;
if ((b = segment.get(JAVA_BYTE, offset++)) == '-') {
negative = true;
}
else {
negative = false;
value = b - '0';
}
while ((b = segment.get(JAVA_BYTE, offset++)) != '\n') {
if (b != '.') {
value = value * 10 + (b - '0');
}
}
int temperature = negative ? -value : value;
addRecord(records, hash, cityBuffer, cityLength, temperature);
}
return records;
}
private static void addRecord(Record[] records, int hash, byte[] cityBuffer, int cityLength, int temperature) {
int idx = hash % records.length;
Record record;
while ((record = records[idx]) != null) {
if (record.hash == hash && Arrays.equals(record.city, 0, record.city.length, cityBuffer, 0, cityLength)) {
record.add(temperature);
return;
}
idx = (idx + 1) % records.length;
}
byte[] city = new byte[cityLength];
System.arraycopy(cityBuffer, 0, city, 0, cityLength);
records[idx] = new Record(hash, city, temperature);
}
private static void mergeResult(TreeMap<String, Record> result, Record[] partialResult) {
for (Record partialRecord : partialResult) {
if (partialRecord == null) {
continue;
}
String cityName = new String(partialRecord.city, UTF_8);
result.compute(cityName, (_, record) -> {
if (record == null) {
return partialRecord;
}
record.merge(partialRecord);
return record;
});
}
}
private record SegmentRange(long startOffset, long endOffset) {
}
private static class Record {
private final int hash;
private final byte[] city;
private int min;
private int max;
private long sum;
private int count;
public Record(int hash, byte[] city, int temperature) {
this.hash = hash;
this.city = city;
this.min = temperature;
this.max = temperature;
this.sum = temperature;
this.count = 1;
}
public void add(int temperature) {
min = min(min, temperature);
max = max(max, temperature);
sum += temperature;
count++;
}
public void merge(Record other) {
min = min(min, other.min);
max = max(max, other.max);
sum += other.sum;
count += other.count;
}
@Override
public String toString() {
return "%.1f/%.1f/%.1f".formatted(
(min / 10.0),
((double) sum / count / 10.0),
(max / 10.0));
}
}
}
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