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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.io.RandomAccessFile;
import java.io.UncheckedIOException;
import java.lang.foreign.Arena;
import java.lang.foreign.MemorySegment;
import java.nio.channels.FileChannel;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.ForkJoinPool;
import java.util.stream.LongStream;
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;
public class CalculateAverage_kgeri {
private static final String FILE = "./measurements.txt";
private static class MeasurementAggregate {
private double min = Double.POSITIVE_INFINITY;
private double sum = 0d;
private double max = Double.NEGATIVE_INFINITY;
private long count;
public void append(double measurement) {
min = Math.min(min, measurement);
max = Math.max(max, measurement);
sum += measurement;
count++;
}
public void merge(MeasurementAggregate other) {
min = Math.min(min, other.min);
max = Math.max(max, other.max);
sum += other.sum;
count += other.count;
}
@Override
public String toString() {
return STR."\{round(min)}/\{round(sum / count)}/\{round(max)}";
}
private double round(double value) {
return Math.round(value * 10.0) / 10.0;
}
}
/**
* This is to avoid instantiating `String`s during processing as much as possible.
*/
private static class StringSlice {
protected final byte[] buf;
protected int len;
protected int hash;
public StringSlice(StringSlice other) {
buf = Arrays.copyOfRange(other.buf, 0, other.len);
len = other.len;
hash = other.hash;
}
public StringSlice(byte[] buf, int len) {
this.buf = buf;
this.len = len;
calculateHash();
}
public int length() {
return len;
}
@Override
public int hashCode() {
return hash;
}
@Override
public boolean equals(Object obj) {
return obj instanceof StringSlice other && Arrays.equals(buf, 0, len, other.buf, 0, other.len);
}
@Override
public String toString() {
return new String(buf, 0, len, UTF_8);
}
protected void calculateHash() {
hash = 1;
for (int i = 0; i < len; i++) {
hash = 31 * hash + buf[i];
}
}
}
/**
* A flyweight of {@link StringSlice}, to avoid instantiating that as well.
*/
private static class MutableStringSlice extends StringSlice {
public MutableStringSlice(byte[] buf) {
super(buf, 0);
}
public void updateLength(int length) {
len = length;
calculateHash();
}
public void clear() {
len = 0;
hash = 0;
}
}
private static Map<StringSlice, MeasurementAggregate> readChunk(FileChannel channel, long from, long chunkSize) {
MemorySegment data;
long remaining;
try {
long offset = Math.max(0, from - 1);
remaining = channel.size() - offset;
data = channel.map(READ_ONLY, offset, Math.min(remaining, chunkSize + 256), Arena.ofConfined()); // +256 to allow for reading records that are split by the chunk
}
catch (IOException e) {
throw new UncheckedIOException(e);
}
long start = 0;
if (from > 0) {
while (data.get(JAVA_BYTE, start++) != '\n') {
}
}
Map<StringSlice, MeasurementAggregate> results = new HashMap<>(1000);
byte[] buf = new byte[256];
MutableStringSlice name = new MutableStringSlice(buf);
long until = Math.min(remaining, chunkSize); // Records may end (slightly) after the chunk boundary, but must not start after it
for (long pos = start; pos < until;) {
name.clear();
int i = 0;
for (;; i++) {
if (pos + i >= data.byteSize()) { // Guard against malformed data (typically a missing newline at the end of the input)
pos = chunkSize;
break;
}
byte b = data.get(JAVA_BYTE, pos + i);
buf[i] = b;
if (b == ';') {
name.updateLength(i);
}
else if (b == '\n') {
pos = pos + i + 1;
break;
}
}
double measurement = parseDoubleFrom(buf, name.length() + 1, i - name.length() - 1);
MeasurementAggregate aggr = results.get(name);
if (aggr == null) {
aggr = new MeasurementAggregate();
results.put(new StringSlice(name), aggr);
}
aggr.append(measurement);
}
return results;
}
// Note: based on java.lang.Integer.parseInt, surely missing some edge cases but avoids allocation
private static double parseDoubleFrom(byte[] buf, int offset, int length) {
boolean negative = false;
int integer = 0;
for (int i = 0; i < length; i++) {
byte c = buf[offset + i];
if (c == '-') {
negative = true;
}
else if (c != '.') {
integer *= 10;
integer -= c - '0';
}
}
return (negative ? integer : -integer) / 10.0;
}
public static void main(String[] args) throws IOException {
Map<String, MeasurementAggregate> measurements = new TreeMap<>();
try (RandomAccessFile raf = new RandomAccessFile(FILE, "r")) {
long size = raf.length();
long threads = Math.min(ForkJoinPool.getCommonPoolParallelism(), Math.max(size / 1000000, 1));
long chunkSize = Math.ceilDiv(size, threads);
System.err.printf("Processing size=%d, threads=%d, chunkSize=%d%n", size, threads, chunkSize);
List<Map<StringSlice, MeasurementAggregate>> chunks = LongStream.range(0, threads)
.parallel()
.mapToObj(i -> readChunk(raf.getChannel(), i * chunkSize, chunkSize))
.toList();
for (Map<StringSlice, MeasurementAggregate> chunk : chunks) {
chunk.forEach((n, m) -> measurements.computeIfAbsent(n.toString(), x -> new MeasurementAggregate()).merge(m));
}
}
System.out.println(measurements);
}
}
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