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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.ByteArrayOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.*;
public class CalculateAverage_jatingala {
private static final String FILE = "./measurements.txt";
public static void main(final String[] args) throws IOException {
final int processorCount = Math.max(Runtime.getRuntime().availableProcessors(), 8);
try (final RandomAccessFile randomAccessFile = new RandomAccessFile(FILE, "r")) {
final long[][] chunks = getChunkPositions(randomAccessFile, processorCount);
final Map<String, Statistics> result = Arrays.stream(chunks)
.parallel()
.map(chunk -> {
try {
final MappedByteBuffer mappedByteBuffer = randomAccessFile.getChannel().map(FileChannel.MapMode.READ_ONLY, chunk[0], chunk[1]);
return consumeChunk(mappedByteBuffer);
}
catch (final Exception e) {
System.out.println(e.getMessage());
return new HashMap<String, Statistics>();
}
})
.reduce((a, b) -> {
a.forEach((k, v) -> {
final Statistics s = b.get(k);
if (s != null)
v.merge(s);
});
b.forEach(a::putIfAbsent);
return a;
})
.orElseGet(Collections::emptyMap);
System.out.println(new TreeMap<>(result));
}
}
private static long[][] getChunkPositions(final RandomAccessFile file, final int chunks) throws IOException {
final long[][] result = new long[chunks][];
final long fileSize = file.length();
final long chunkSize = Math.ceilDiv(fileSize, chunks);
long chunkStartPosition = 0;
for (int i = 0; i < chunks; i++) {
file.seek(Math.min(chunkStartPosition + chunkSize, fileSize));
while (file.getFilePointer() < fileSize && file.readByte() != '\n') {
// find next newline, noop
}
// startPointer & length
result[i] = new long[]{ chunkStartPosition, file.getFilePointer() - chunkStartPosition };
chunkStartPosition = file.getFilePointer();
}
return result;
}
private static Map<String, Statistics> consumeChunk(final MappedByteBuffer mappedByteBuffer) {
final Map<String, Statistics> statisticsMap = new HashMap<>();
while (mappedByteBuffer.hasRemaining()) {
final String key = parseKey(mappedByteBuffer);
final double value = parseNumber(mappedByteBuffer);
statisticsMap.computeIfAbsent(key, _ -> new Statistics()).update(value);
}
return statisticsMap;
}
private static String parseKey(final MappedByteBuffer mappedByteBuffer) {
final ByteArrayOutputStream keyBytes = new ByteArrayOutputStream();
while (mappedByteBuffer.hasRemaining()) {
final byte val = mappedByteBuffer.get();
if (val == ';')
break;
keyBytes.write(val);
}
return keyBytes.toString();
}
private static double parseNumber(final MappedByteBuffer mappedByteBuffer) {
boolean negate = false;
int temp = 0;
while (mappedByteBuffer.hasRemaining()) {
final byte val = mappedByteBuffer.get();
if (val == '\n')
break;
if (val == '-') {
negate = true;
continue;
}
if (val == '.')
continue;
temp = 10 * temp + (val - '0');
}
return (negate ? -1 : 1) * (temp / 10.0);
}
private static class Statistics {
private double min = Double.POSITIVE_INFINITY;
private double max = Double.NEGATIVE_INFINITY;
private double sum;
private long count;
private static double round(final double value) {
return Math.round(value * 10.0) / 10.0;
}
public void update(final double reading) {
this.min = Math.min(min, reading);
this.max = Math.max(max, reading);
this.sum += reading;
++count;
}
public void merge(final Statistics other) {
this.min = Math.min(min, other.min);
this.max = Math.max(max, other.max);
this.sum += other.sum;
this.count += other.count;
}
@Override
public String toString() {
return STR."\{round(min)}/\{round(sum / count)}/\{round(max)}";
}
}
}
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