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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.HashMap;
import java.util.List;
import java.util.Map;
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 = fileSize > 10_000 ? min(Integer.MAX_VALUE - 256, fileSize / cpus) : 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<Map<ByteWrapper, Record>>> futures = new ArrayList<>();
for (SegmentRange range : rangeList) {
futures.add(supplyAsync(() -> process(range, segment), executor));
}
for (CompletableFuture<Map<ByteWrapper, Record>> future : futures) {
try {
Map<ByteWrapper, Record> partialResult = future.get();
combine(result, partialResult);
}
catch (InterruptedException | ExecutionException ex) {
throw new RuntimeException(ex);
}
}
}
System.out.println(result);
}
private static Map<ByteWrapper, Record> process(SegmentRange range, MemorySegment segment) {
Map<ByteWrapper, Record> partialResult = new HashMap<>(1_000);
byte[] buffer = new byte[100];
long offset = range.startOffset;
byte b;
while (offset < range.endOffset) {
int cityIdx = 0;
while ((b = segment.get(JAVA_BYTE, offset++)) != ';') {
buffer[cityIdx++] = b;
}
byte[] city = new byte[cityIdx];
System.arraycopy(buffer, 0, city, 0, cityIdx);
ByteWrapper cityWrapper = new ByteWrapper(city);
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;
partialResult.compute(cityWrapper, (_, record) -> update(record, temperature));
}
return partialResult;
}
private record SegmentRange(long startOffset, long endOffset) {
}
private record ByteWrapper(byte[] bytes) {
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
ByteWrapper that = (ByteWrapper) o;
return Arrays.equals(bytes, that.bytes);
}
@Override
public int hashCode() {
return Arrays.hashCode(bytes);
}
}
private static class Record {
private int min;
private int max;
private long sum;
private int count;
public Record(int temperature) {
this.min = temperature;
this.max = temperature;
this.sum = temperature;
this.count = 1;
}
@Override
public String toString() {
return "%.1f/%.1f/%.1f".formatted(
(min / 10.0),
((double) sum / count / 10.0),
(max / 10.0));
}
}
private static Record update(Record record, int temperature) {
if (record == null) {
return new Record(temperature);
}
record.min = min(record.min, temperature);
record.max = max(record.max, temperature);
record.sum += temperature;
record.count++;
return record;
}
private static void combine(TreeMap<String, Record> result, Map<ByteWrapper, Record> partialResult) {
partialResult.forEach((wrapper, partialRecord) -> {
String city = new String(wrapper.bytes, UTF_8);
result.compute(city, (_, record) -> {
if (record == null) {
return partialRecord;
}
record.min = min(record.min, partialRecord.min);
record.max = max(record.max, partialRecord.max);
record.sum += partialRecord.sum;
record.count += partialRecord.count;
return record;
});
});
}
}
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