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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.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.TreeMap;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class CalculateAverage_seijikun {
private static final String FILE = "./measurements.txt";
private static class MeasurementAggregator {
private double min = Double.POSITIVE_INFINITY;
private double max = Double.NEGATIVE_INFINITY;
private double sum;
private long count;
public void printInto(PrintStream out) {
out.printf("%.1f/%.1f/%.1f", min, (sum / (double) count), max);
}
}
public static class StationIdent implements Comparable<StationIdent> {
private final int nameLength;
private final String name;
private final int nameHash;
public StationIdent(byte[] name, int nameHash) {
this.nameLength = name.length;
this.name = new String(name);
this.nameHash = nameHash;
}
@Override
public int hashCode() {
return nameHash;
}
@Override
public boolean equals(Object obj) {
var other = (StationIdent) obj;
if (other.nameLength != nameLength) {
return false;
}
return name.equals(other.name);
}
@Override
public int compareTo(StationIdent o) {
return name.compareTo(o.name);
}
}
public static class ChunkReader implements Runnable {
RandomAccessFile file;
// Start offset of this chunk
private final long startOffset;
// end offset of this chunk
private final long endOffset;
// state
private MappedByteBuffer buffer = null;
private int ptr = 0;
private TreeMap<StationIdent, MeasurementAggregator> workSet;
public ChunkReader(RandomAccessFile file, long startOffset, long endOffset) {
this.file = file;
this.startOffset = startOffset;
this.endOffset = endOffset;
}
private StationIdent readStationName() {
int startPtr = ptr;
int hashCode = 0;
int hashBytePtr = 0;
byte c;
while ((c = buffer.get(ptr++)) != ';') {
hashCode ^= ((int) c) << (hashBytePtr * 8);
hashBytePtr = (hashBytePtr + 1) % 4;
}
byte[] stationNameBfr = new byte[ptr - startPtr - 1];
buffer.get(startPtr, stationNameBfr);
return new StationIdent(stationNameBfr, hashCode);
}
private double readTemperature() {
double ret = 0, div = 1;
byte c = buffer.get(ptr++);
boolean neg = (c == '-');
if (neg)
c = buffer.get(ptr++);
do {
ret = ret * 10 + c - '0';
} while ((c = buffer.get(ptr++)) >= '0' && c <= '9');
if (c == '.') {
while ((c = buffer.get(ptr++)) != '\n') {
ret += (c - '0') / (div *= 10);
}
}
if (neg)
return -ret;
return ret;
}
@Override
public void run() {
workSet = new TreeMap<>();
int chunkSize = (int) (endOffset - startOffset);
try {
buffer = file.getChannel().map(FileChannel.MapMode.READ_ONLY, startOffset, chunkSize);
while (ptr < chunkSize) {
var station = readStationName();
var temp = readTemperature();
var stationWorkSet = workSet.get(station);
if (stationWorkSet == null) {
stationWorkSet = new MeasurementAggregator();
workSet.put(station, stationWorkSet);
}
stationWorkSet.min = Math.min(temp, stationWorkSet.min);
stationWorkSet.max = Math.max(temp, stationWorkSet.max);
stationWorkSet.sum += temp;
stationWorkSet.count += 1;
}
}
catch (IOException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
public static void main(String[] args) throws IOException, InterruptedException {
RandomAccessFile file = new RandomAccessFile(FILE, "r");
int jobCnt = Runtime.getRuntime().availableProcessors();
var chunks = new ChunkReader[jobCnt];
long chunkSize = file.length() / jobCnt;
long chunkStartPtr = 0;
byte[] tmpBuffer = new byte[128];
for (int i = 0; i < jobCnt; ++i) {
long chunkEndPtr = chunkStartPtr + chunkSize;
if (i != (jobCnt - 1)) { // align chunks to newlines
file.seek(chunkEndPtr - 1);
file.read(tmpBuffer);
int offset = 0;
while (tmpBuffer[offset] != '\n') {
offset += 1;
}
chunkEndPtr += offset;
}
else { // last chunk ends at file end
chunkEndPtr = file.length();
}
chunks[i] = new ChunkReader(file, chunkStartPtr, chunkEndPtr);
chunkStartPtr = chunkEndPtr;
}
try(var executor = Executors.newFixedThreadPool(jobCnt)) {
for (int i = 0; i < jobCnt; ++i) {
executor.submit(chunks[i]);
}
executor.shutdown();
var ignored = executor.awaitTermination(1, TimeUnit.DAYS);
}
// merge chunks
var result = chunks[0].workSet;
for (int i = 1; i < jobCnt; ++i) {
chunks[i].workSet.forEach((ident, otherStationWorkSet) -> {
var stationWorkSet = result.get(ident);
if (stationWorkSet == null) {
result.put(ident, otherStationWorkSet);
}
else {
stationWorkSet.min = Math.min(stationWorkSet.min, otherStationWorkSet.min);
stationWorkSet.max = Math.max(stationWorkSet.max, otherStationWorkSet.max);
stationWorkSet.sum += otherStationWorkSet.sum;
stationWorkSet.count += otherStationWorkSet.count;
}
});
}
// print in required format
System.out.write('{');
var iterator = result.entrySet().iterator();
while (iterator.hasNext()) {
var entry = iterator.next();
System.out.print(entry.getKey().name);
System.out.write('=');
entry.getValue().printInto(System.out);
if (iterator.hasNext()) {
System.out.print(", ");
}
}
System.out.println('}');
}
}
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