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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.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import static java.nio.channels.FileChannel.MapMode.READ_ONLY;
import static java.nio.file.StandardOpenOption.READ;
public class CalculateAverage_semotpan {
private static final Path FILE = Path.of("./measurements.txt");
public static void main(String[] args) throws IOException, InterruptedException {
var spliterator = new SegmentSpliterator(FILE);
var summaryStations = IntStream.range(0, spliterator.segments)
.parallel()
.mapToObj(segment -> {
var buff = spliterator.buffSegment(segment);
return new SegmentReader(buff);
})
.flatMap(segmentReader -> segmentReader.values().stream())
.collect(Collectors.groupingByConcurrent(StationSummary::station));
// Complexity: O(stations * segments)
var output = new TreeMap<String, StationSummary>();
summaryStations.forEach((station, summaries) -> {
var summary = summaries.stream()
.reduce(new StationSummary(), (identity, acc) -> {
identity.min = Integer.min(identity.min, acc.min);
identity.max = Integer.max(identity.max, acc.max);
identity.sum += acc.sum;
identity.count += acc.count;
return identity;
});
output.put(station, summary);
});
System.out.println(output);
}
private static class StationSummary {
public String station;
public int min, max, sum, count;
StationSummary() {
min = Integer.MAX_VALUE;
max = Integer.MIN_VALUE;
}
StationSummary(String station, int temperature) {
this.station = station;
this.min = this.max = this.sum = temperature;
this.count = 1;
}
String station() {
return station;
}
private double round(double value) {
return Math.round(value * 10.0) / 10.0;
}
@Override
public String toString() {
return new StringBuilder()
.append(round((double) min * 0.1)).append('/')
.append(round((double) sum * 0.1 / count))
.append('/').append(round((double) max * 0.1))
.toString();
}
}
static class SegmentSpliterator {
private int segments;
private final ByteBuffer[] buffSegments;
SegmentSpliterator(Path file) throws IOException {
this.segments = Runtime.getRuntime().availableProcessors();
var fileSize = Files.size(file);
var segmentSize = fileSize / segments;
if (segmentSize <= (1 << 8)) { // small segment: 1 is enough
segments = 1;
}
buffSegments = new ByteBuffer[segments];
var pos = 0L;
for (var s = 0; s < segments - 1; s++) {
try (var channel = (FileChannel) Files.newByteChannel(FILE, READ)) {
var buff = channel.map(READ_ONLY, pos, segmentSize);
pos = normalize(buff, (int) segmentSize - 1, pos);
buffSegments[s] = buff;
}
}
// handle last segment
try (var channel = (FileChannel) Files.newByteChannel(FILE, READ)) {
var buff = channel.map(READ_ONLY, pos, fileSize - pos);
buffSegments[segments - 1] = buff;
}
}
private long normalize(ByteBuffer buff, int relativePos, long pos) {
while (buff.get(relativePos) != '\n') {
relativePos--;
}
buff.limit(relativePos + 1);
return pos + (relativePos + 1);
}
ByteBuffer buffSegment(int index) {
return buffSegments[index];
}
}
static class SegmentReader {
private final Map<String, StationSummary> accumulator;
private final byte[] keyBuff = new byte[256];
SegmentReader(ByteBuffer byteBuffer) {
accumulator = new HashMap<>();
read(byteBuffer);
}
private void read(ByteBuffer buff) {
byte b;
for (int pos = 0, limit = buff.limit(); buff.hasRemaining(); buff.position(pos)) {
// parse station (key)
int offset = 0;
while ((b = buff.get(pos++)) != ';') {
keyBuff[offset++] = b;
}
// parse temperature (value) as int (1.1 * 10 = 11)
int temp = 0;
int negative = 1;
while (pos != limit && (b = buff.get(pos++)) != '\n') {
switch (b) {
case '-':
negative = -1;
case '.':
continue;
default:
temp = 10 * temp + (b - '0');
}
}
temp *= negative;
// compute station
var station = new String(keyBuff, 0, offset);
var finalTemp = temp;
accumulator.compute(station, (key, summary) -> {
if (summary == null) {
return new StationSummary(station, finalTemp);
}
summary.min = Integer.min(summary.min, finalTemp);
summary.max = Integer.max(summary.max, finalTemp);
summary.sum += finalTemp;
summary.count += 1;
return summary;
});
}
}
Collection<StationSummary> values() {
return accumulator.values();
}
}
}
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