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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.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
public class CalculateAverage_manishgarg90 {
private static final String FILE = "./measurements.txt";
private static int nProcessors = Runtime.getRuntime().availableProcessors();
public static void main(String[] args) throws IOException {
try (FileChannel channel = FileChannel.open(Paths.get(FILE), StandardOpenOption.READ)) {
long fileSize = channel.size();
long chunkSize = (fileSize + nProcessors - 1) / nProcessors;
long pos = 0;
List<MappedByteBuffer> buffers = new ArrayList<>(nProcessors);
for (int i = 0; i < nProcessors; i++) {
long endPosition = getEndPosition(channel, pos + chunkSize);
long size = endPosition - pos;
MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, pos, size);
pos = pos + size;
buffers.add(buffer);
}
Map<String, Stat> s = readBufferAndCalculateMeauremenst(buffers);
Map<String, Stat> tm = new TreeMap<String, Stat>(s);
System.out.println(tm);
}
catch (IOException e) {
e.printStackTrace();
}
}
private static Map<String, Stat> readBufferAndCalculateMeauremenst(List<MappedByteBuffer> chunks) {
return chunks.parallelStream().map(buffer -> {
Map<String, Stat> map = new HashMap<>(10_000, 1);
int lineStart = 0;
int doubleStart = 0;
int length = buffer.limit();
String station = null;
for (int i = 0; i < length; ++i) {
byte b = buffer.get(i);
if (b == ';') {
byte[] stationBuffer = new byte[i - lineStart];
buffer.position(lineStart);
buffer.get(stationBuffer);
station = new String(stationBuffer, StandardCharsets.UTF_8);
doubleStart = i + 1;
}
else if (b == '\n') {
byte[] doubleBuffer = new byte[i - doubleStart];
buffer.position(doubleStart);
buffer.get(doubleBuffer);
Double temperature = Double.parseDouble(new String(doubleBuffer));
lineStart = i + 1;
// I have station name and temp
Stat s = map.get(station);
if (s == null) {
map.put(station, new Stat(temperature));
}
else {
s.update(temperature);
}
}
}
return map;
}).reduce(new HashMap<>(), (map1, map2) -> {
Stat s = new Stat();
s.merge(map1);
s.merge(map2);
return s.getResultMap();
});
}
private static long getEndPosition(FileChannel channel, long position) throws IOException {
ByteBuffer buffer = ByteBuffer.allocate(1);
while (position < channel.size()) {
channel.read(buffer, position);
if (buffer.get(0) == '\n') {
return position + 1;
}
position++;
buffer.clear();
}
return channel.size();
}
private static final class Stat {
private Double min = Double.MAX_VALUE;
private Double max = Double.MIN_VALUE;
private Double sum = 0d;
private long count = 0L;
private Map<String, Stat> resultMap = null;
public Stat() {
this.resultMap = new HashMap<>(10_000, 1);
}
public Stat(Double value) {
this.min = value;
this.max = value;
this.sum += value;
this.count++;
}
private void update(Double value) {
this.min = Math.min(this.min, value);
this.max = Math.max(this.max, value);
this.sum = round(this.sum + value);
this.count++;
}
private void merge(Map<String, Stat> result) {
result.forEach((city, resultRow) -> resultMap.merge(city, resultRow, (existing, incoming) -> {
existing.min = Math.min(existing.min, incoming.min);
existing.max = Math.max(existing.max, incoming.max);
existing.sum += incoming.sum;
existing.count += incoming.count;
return existing;
}));
}
public Map<String, Stat> getResultMap() {
return resultMap;
}
private double round(double value) {
return Math.round(value * 10.0) / 10.0;
}
@Override
public String toString() {
return round(min) + "/" + round(sum / count) + "/" + round(max);
}
}
}
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