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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.charset.StandardCharsets;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Arrays;
import java.util.List;
import java.util.TreeMap;
public class CalculateAverage_ebarlas {
private static final int MAX_KEY_SIZE = 100;
private static final int HASH_FACTOR = 433;
private static final int HASH_TBL_SIZE = 16_383; // range of allowed hash values, inclusive
public static void main(String[] args) throws IOException, InterruptedException {
if (args.length != 2) {
System.out.println("Usage: java CalculateAverage <input-file> <partitions>");
System.exit(1);
}
var path = Paths.get(args[0]);
var numPartitions = Integer.parseInt(args[1]);
var channel = FileChannel.open(path, StandardOpenOption.READ);
var partitionSize = channel.size() / numPartitions;
var partitions = new Partition[numPartitions];
var threads = new Thread[numPartitions];
for (int i = 0; i < numPartitions; i++) {
var pIdx = i;
var pStart = pIdx * partitionSize;
var pEnd = pIdx == numPartitions - 1
? channel.size() // last partition might be slightly larger
: pStart + partitionSize;
var pSize = pEnd - pStart;
Runnable r = () -> {
try {
var buffer = channel.map(FileChannel.MapMode.READ_ONLY, pStart, pSize);
partitions[pIdx] = processBuffer(buffer, pIdx == 0);
}
catch (IOException e) {
throw new RuntimeException(e);
}
};
threads[i] = new Thread(r);
threads[i].start();
}
for (var thread : threads) {
thread.join();
}
var partitionList = List.of(partitions);
foldFootersAndHeaders(partitionList);
printResults(foldStats(partitionList));
}
private static void printResults(Stats[] stats) { // adheres to Gunnar's reference code
var result = new TreeMap<String, String>();
for (var st : stats) {
if (st != null) {
var key = new String(st.key, StandardCharsets.UTF_8);
result.put(key, format(st));
}
}
System.out.println(result);
}
private static String format(Stats st) { // adheres to expected output format
return round(st.min / 10.0) + "/" + round((st.sum / 10.0) / st.count) + "/" + round(st.max / 10.0);
}
private static double round(double value) { // Gunnar's round function
return Math.round(value * 10.0) / 10.0;
}
private static Stats[] foldStats(List<Partition> partitions) { // fold stats from all partitions into first partition
var target = partitions.getFirst().stats;
for (int i = 1; i < partitions.size(); i++) {
var current = partitions.get(i).stats;
for (int j = 0; j < current.length; j++) {
if (current[j] != null) {
var t = findInTable(target, current[j].hash, current[j].key, current[j].key.length);
t.min = Math.min(t.min, current[j].min);
t.max = Math.max(t.max, current[j].max);
t.sum += current[j].sum;
t.count += current[j].count;
}
}
}
return target;
}
private static void foldFootersAndHeaders(List<Partition> partitions) { // fold footers and headers into prev partition
for (int i = 1; i < partitions.size(); i++) {
var pNext = partitions.get(i);
var pPrev = partitions.get(i - 1);
var merged = mergeFooterAndHeader(pPrev.footer, pNext.header);
if (merged != null) {
if (merged[merged.length - 1] == '\n') { // fold into prev partition
doProcessBuffer(ByteBuffer.wrap(merged), true, pPrev.stats);
}
else { // no newline appeared in partition, carry forward
pNext.footer = merged;
}
}
}
}
private static byte[] mergeFooterAndHeader(byte[] footer, byte[] header) {
if (footer == null) {
return header;
}
if (header == null) {
return footer;
}
var merged = new byte[footer.length + header.length];
System.arraycopy(footer, 0, merged, 0, footer.length);
System.arraycopy(header, 0, merged, footer.length, header.length);
return merged;
}
private static Partition processBuffer(ByteBuffer buffer, boolean first) {
return doProcessBuffer(buffer, first, new Stats[HASH_TBL_SIZE + 1]);
}
private static Partition doProcessBuffer(ByteBuffer buffer, boolean first, Stats[] stats) {
var header = first ? null : readHeader(buffer);
var readingKey = true; // reading key or value?
var keyBuf = new byte[MAX_KEY_SIZE]; // buffer for key
var keyPos = 0; // current position in key buffer
var keyHash = 0; // accumulating hash of key
var keyStart = buffer.position(); // start of key in buffer used for footer calc
var negative = false; // is value negative?
var val = 0; // accumulating value
Stats st = null;
while (buffer.hasRemaining()) {
var b = buffer.get();
if (readingKey) {
if (b != ';') {
keyHash = HASH_FACTOR * keyHash + b;
keyBuf[keyPos++] = b;
}
else {
var idx = keyHash & HASH_TBL_SIZE;
st = stats[idx];
if (st == null) { // nothing in table, eagerly claim spot
st = stats[idx] = newStats(keyBuf, keyPos, keyHash);
}
else if (!Arrays.equals(st.key, 0, st.key.length, keyBuf, 0, keyPos)) {
st = findInTable(stats, keyHash, keyBuf, keyPos);
}
readingKey = false;
}
}
else {
if (b == '\n') {
var v = negative ? -val : val;
st.min = Math.min(st.min, v);
st.max = Math.max(st.max, v);
st.sum += v;
st.count++;
readingKey = true;
keyHash = 0;
val = 0;
negative = false;
keyStart = buffer.position();
keyPos = 0;
}
else if (b == '-') {
negative = true;
}
else if (b != '.') { // skip '.' since fractional tenth unit after decimal point is assumed
val = val * 10 + (b - '0');
}
}
}
var footer = keyStart < buffer.position() ? readFooter(buffer, keyStart) : null;
return new Partition(header, footer, stats);
}
private static Stats findInTable(Stats[] stats, int hash, byte[] key, int len) { // open-addressing scan
var idx = hash & HASH_TBL_SIZE;
var st = stats[idx];
while (st != null && !Arrays.equals(st.key, 0, st.key.length, key, 0, len)) {
idx = (idx + 1) % (HASH_TBL_SIZE + 1);
st = stats[idx];
}
if (st != null) {
return st;
}
return stats[idx] = newStats(key, len, hash);
}
private static Stats newStats(byte[] buffer, int len, int hash) {
var k = new byte[len];
System.arraycopy(buffer, 0, k, 0, len);
return new Stats(k, hash);
}
private static byte[] readFooter(ByteBuffer buffer, int lineStart) { // read from line start to current pos (end-of-input)
var footer = new byte[buffer.position() - lineStart];
buffer.get(lineStart, footer, 0, footer.length);
return footer;
}
private static byte[] readHeader(ByteBuffer buffer) { // read up to and including first newline (or end-of-input)
while (buffer.hasRemaining() && buffer.get() != '\n')
;
var header = new byte[buffer.position()];
buffer.get(0, header, 0, header.length);
return header;
}
private static class Partition {
byte[] header;
byte[] footer;
Stats[] stats;
Partition(byte[] header, byte[] footer, Stats[] stats) {
this.header = header;
this.footer = footer;
this.stats = stats;
}
}
private static class Stats { // min, max, and sum values are modeled with integral types that represent tenths of a unit
final byte[] key;
final int hash;
int min = Integer.MAX_VALUE;
int max = Integer.MIN_VALUE;
long sum;
long count;
Stats(byte[] key, int hash) {
this.key = key;
this.hash = hash;
}
}
}
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