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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.*;
import java.nio.channels.*;
import java.nio.file.*;
import java.util.*;
import java.util.stream.*;
public class CalculateAverage_rby {
private static final String FILE = "./measurements.txt";
// private static final int CHUNK_SIZE = 8 * 1024 * 1024;
private static final int CHUNK_SIZE = 32 << 20;
/**
* Computes good enough partitions which end on a newline
*/
static long[] cuts(Path p, int workers) throws IOException {
var channel = (FileChannel) Files.newByteChannel(p, EnumSet.of(StandardOpenOption.READ));
final long size = channel.size();
if (size < 10000l) {
return new long[]{ 0l, size };
}
long chunk = size / workers;
long position = size - chunk;
long[] cuts = new long[workers + 1];
cuts[workers] = size;
// 1024 should cover enough to catch a newline
var buf = ByteBuffer.allocateDirect(1024);
byte[] bytes = new byte[1024];
while (workers-- > 0) {
var read = channel.read(buf, position);
buf.flip();
buf.get(bytes, 0, read);
var nextNL = position;
while (read-- > 0) {
if (bytes[read] == '\n') {
nextNL += read;
cuts[workers] = nextNL;
break;
}
}
position -= chunk;
buf.rewind();
}
cuts[0] = 0L;
return cuts;
}
public static void main(String[] args) throws IOException {
var p = Paths.get(FILE);
var cpus = Runtime.getRuntime().availableProcessors();
final long[] cuts = cuts(p, cpus);
var stats = IntStream.range(0, cuts.length - 1)
.parallel()
.mapToObj((i) -> stats(p, cuts[i], cuts[i + 1]))
.reduce(Stats.IDENTITY, Stats::combine);
stats.print();
}
static record Stats(Map<String, Integer> indexes, int nextIx, int[] stats) {
private final static Stats IDENTITY = new Stats(new HashMap(), 0, new int[0]);
// not much optimization needed here
Stats combine(Stats other) {
if (this == IDENTITY) return other;
if (other == IDENTITY) return this;
var myNextIx = nextIx;
for(var e : other.indexes.entrySet()) {
int ix;
var ixi = indexes.get(e.getKey());
if ( ixi == null) {
ix = myNextIx++ * 4;
} else {
ix = ixi.intValue() * 4;
}
var oix = e.getValue() * 4;
stats[ix] = Math.min(stats[ix], other.stats[oix]);
stats[ix + 1] = Math.max(stats[ix + 1], other.stats[oix + 1]);
stats[ix + 2] += other.stats[oix + 2];
stats[ix + 3] += other.stats[oix + 3];
}
return new Stats(indexes, myNextIx, stats);
}
// or here
void print() {
var iter = new TreeMap<>(indexes).entrySet().iterator();
System.out.print("{");
if (iter.hasNext()) {
var e = iter.next();
var ix = e.getValue().intValue() * 4;
var avg = Math.round(stats[ix + 2]/((double)stats[ix+3]))/10.0;
System.out.print(e.getKey() + "="
+ (stats[ix]/10.0) + "/"
+ avg + "/"
+ (stats[ix + 1]/10.0));
}
while(iter.hasNext()) {
var e = iter.next();
var ix = e.getValue().intValue() * 4;
var avg = Math.round(stats[ix + 2]/((double)stats[ix+3]))/10.0;
System.out.print(", " + e.getKey() + "="
+ (stats[ix]/10.0) + "/"
+ avg + "/"
+ (stats[ix + 1]/10.0)) ;
}
System.out.println("}");
}
}
static final int MAX_CITIES = 1000;
static final int ARRAY_SIZE = 1 << 20;
static Stats stats(Path p, long start, long end) {
int nextCityIx = 0;
var cityIndexes = new HashMap<String, Integer>(MAX_CITIES, 1.0f);
int[] stats = new int[MAX_CITIES * 4];
for (int i = 0; i < MAX_CITIES; i++) {
stats[i * 4] = Integer.MAX_VALUE;
stats[i * 4 + 1] = Integer.MIN_VALUE;
}
try {
final var channel = (FileChannel) Files.newByteChannel(p, EnumSet.of(StandardOpenOption.READ));
channel.position(start);
var offset = start;
final byte[] array = new byte[ARRAY_SIZE];
// the next expected char, the most simple stateMachine
char nextChar = ';';
// good enough for a city name, or a double
byte[] strbuff = new byte[128];
int strbuffIx = 0;
int cityIndex = 0;
final var buffer = ByteBuffer.allocateDirect(CHUNK_SIZE);
while (offset < end) {
final int limit = channel.read(buffer);
if (limit <= 0)
break;
offset += limit;
int totalRead = 0;
buffer.flip();
while (totalRead < limit) {
int read = Math.min(array.length, limit - totalRead);
buffer.get(array, 0, read);
totalRead += read;
for (int i = 0; i < read; i++) {
if (nextChar == '\n' && array[i] == '.')
continue;
strbuff[strbuffIx++] = array[i];
if (array[i] == nextChar) {
var str = new String(strbuff, 0, strbuffIx - 1, "utf8");
strbuffIx = 0;
switch (nextChar) {
case ';':
nextChar = '\n';
var mbCityIx = cityIndexes.get(str);
if (mbCityIx == null) {
cityIndex = nextCityIx;
cityIndexes.put(str, nextCityIx++);
if (nextCityIx * 4 >= stats.length) {
var newStats = Arrays.copyOf(stats, stats.length * 2);
for (int j = stats.length; j < newStats.length; j += 4) {
newStats[j] = Integer.MAX_VALUE;
newStats[j + 1] = Integer.MIN_VALUE;
}
stats = newStats;
}
}
else {
cityIndex = mbCityIx.intValue();
}
break;
case '\n':
nextChar = ';';
int temp = Integer.parseInt(str);
var ix = cityIndex * 4;
if (temp < stats[ix])
stats[ix] = temp;
if (temp > stats[ix + 1])
stats[ix + 1] = temp;
stats[ix + 2] += temp;
stats[ix + 3]++;
break;
default:
}
}
}
}
buffer.rewind();
}
return new Stats(cityIndexes, nextCityIx, stats);
}
catch (IOException err) {
return null;
}
}
}
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