My own solution -- memory mapping the files, running in parallel thre…

…ads, using a state machine to parse the file (#466)

* Golang implementation

* Speed up by avoiding copying the lines

* Memory mapping

* Add script for testing

* Now passing most of the tests

* Refactor to composed method

* Now using integer math throughout

* Now using a state machine for parsing!

* Refactoring state names

* Enabling profiling

* Running in parallel!

* Fully parallel!

* Refactor

* Improve type safety of methods

* The rounding problem is due to difference between Javas and Gos printf implementation

* Converting my solution to Java

* Merging results

* Splitting the file in several buffers

* Made it parallel!

* Removed test file

* Removed go implementation

* Removed unused files

* Add header to .sh file

---------

Co-authored-by: Matteo Vaccari <mvaccari@thoughtworks.com>

calculate_average_xpmatteo.sh

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+#!/bin/sh
+#
+#  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.
+#
+
+JAVA_OPTS="--enable-preview"
+java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_xpmatteo
+

src/main/java/dev/morling/onebrc/CalculateAverage_xpmatteo.java

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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.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.TreeMap;
+import java.util.stream.Collectors;
+
+@SuppressWarnings({ "ReassignedVariable", "StatementWithEmptyBody" })
+public class CalculateAverage_xpmatteo {
+
+    private static final String FILE = "./measurements.txt";
+
+    public static void main(String[] args) throws IOException, InterruptedException {
+        var fileName = dataFileName(args);
+
+        try (
+                var file = new RandomAccessFile(new File(fileName), "r");
+                var channel = file.getChannel()) {
+            var numCpus = Runtime.getRuntime().availableProcessors();
+            var threads = split(channel, numCpus).stream()
+                    .map(Worker::new)
+                    .toList();
+            threads.forEach(Thread::start);
+            for (Worker thread : threads) {
+                thread.join();
+            }
+            var results = threads.stream().map(Worker::getResults)
+                    .reduce(CalculateAverage_xpmatteo::merge)
+                    .orElseThrow();
+            printCities(results);
+        }
+    }
+
+    public static class Worker extends Thread {
+        private final ByteBuffer buffer;
+        private Results results;
+
+        public Worker(ByteBuffer buffer) {
+            this.buffer = buffer;
+        }
+
+        @Override
+        public void run() {
+            this.results = parseData(this.buffer);
+        }
+
+        public Results getResults() {
+            return results;
+        }
+    }
+
+    protected static List<ByteBuffer> split(FileChannel channel, int numCpus) throws IOException {
+        if (channel.size() < 10_000) {
+            return List.of(channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size()));
+        }
+
+        long[] increments = new long[numCpus + 1];
+        for (int i = 0; i < numCpus; i++) {
+            increments[i] = i * channel.size() / numCpus;
+            // adjust the increments so that they start on the beginning of a city
+            while (increments[i] > 0 && byteAt(channel, increments[i] - 1) != '\n') {
+                increments[i]--;
+            }
+        }
+        increments[numCpus] = channel.size();
+
+        List<ByteBuffer> result = new ArrayList<>(numCpus);
+        for (int i = 0; i < numCpus; i++) {
+            long from = increments[i];
+            long to = increments[i + 1];
+            result.add(channel.map(FileChannel.MapMode.READ_ONLY, from, to - from));
+        }
+        return result;
+    }
+
+    private static byte byteAt(FileChannel channel, long offset) throws IOException {
+        ByteBuffer buf = ByteBuffer.allocate(1);
+        channel.position(offset);
+        channel.read(buf);
+        buf.flip();
+        var bytes = new byte[1];
+        buf.get(bytes);
+        return bytes[0];
+    }
+
+    public static String dataFileName(String[] args) {
+        if (args.length == 1) {
+            return args[0];
+        }
+        return FILE;
+    }
+
+    protected static byte[] readAllData(String fileName) throws IOException {
+        return Files.readAllBytes(Path.of(fileName));
+    }
+
+    protected static ByteBuffer memoryMap(String fileName) throws IOException {
+        try (RandomAccessFile file = new RandomAccessFile(new File(fileName), "r")) {
+            // Get file channel in read-only mode
+            FileChannel fileChannel = file.getChannel();
+
+            return fileChannel.map(FileChannel.MapMode.READ_ONLY, 0, fileChannel.size());
+        }
+    }
+
+    protected enum State {
+        PARSING_CITY_NAME,
+        SKIPPING_SEMICOLON,
+        PARSING_TEMPERATURE
+    }
+
+    protected static Results parseData(ByteBuffer data) {
+        var results = new Results();
+        var state = State.PARSING_CITY_NAME;
+        int cityStartOffset = 0, cityEndOffset = 0;
+        int temp = 0, sign = 0;
+
+        for (int i = 0; i < data.limit(); i++) {
+            byte currentChar = data.get();
+            if (state == State.PARSING_CITY_NAME && currentChar == ';') {
+                state = State.SKIPPING_SEMICOLON;
+                cityEndOffset = i;
+            }
+            else if (state == State.PARSING_CITY_NAME) {
+                // do nothing
+            }
+            else if (state == State.SKIPPING_SEMICOLON && currentChar == '-') {
+                state = State.PARSING_TEMPERATURE;
+                temp = 0;
+                sign = -1;
+            }
+            else if (state == State.SKIPPING_SEMICOLON && currentChar >= '0' && currentChar <= '9') {
+                state = State.PARSING_TEMPERATURE;
+                temp = currentChar - '0';
+                sign = 1;
+            }
+            else if (state == State.PARSING_TEMPERATURE && currentChar >= '0' && currentChar <= '9') {
+                temp = temp * 10 + currentChar - '0';
+            }
+            else if (state == State.PARSING_TEMPERATURE && currentChar == '.') {
+                // do nothing
+            }
+            else if (state == State.PARSING_TEMPERATURE && currentChar == '\n') {
+                byte[] bytes = new byte[cityEndOffset - cityStartOffset];
+                data.get(cityStartOffset, bytes);
+                var cityName = new String(bytes);
+                accumulate(results, cityName, temp * sign);
+                state = State.PARSING_CITY_NAME;
+                cityStartOffset = i + 1;
+            }
+        }
+
+        return results;
+    }
+
+    private static void accumulate(Results results, String cityName, int tempTimesTen) {
+        var existing = results.get(cityName);
+        if (existing == null) {
+            results.put(cityName, new CityData(tempTimesTen, tempTimesTen, tempTimesTen, 1));
+        }
+        else {
+            existing.min = Math.min(existing.min, tempTimesTen);
+            existing.sum = existing.sum + tempTimesTen;
+            existing.max = Math.max(existing.max, tempTimesTen);
+            existing.count++;
+        }
+    }
+
+    protected static Results merge(Results a, Results b) {
+        for (var entry : b.entrySet()) {
+            CityData valueInA = a.get(entry.getKey());
+            if (null == valueInA) {
+                a.put(entry.getKey(), entry.getValue());
+            }
+            else {
+                var valueInB = entry.getValue();
+                valueInA.min = Math.min(valueInA.min, valueInB.min);
+                valueInA.sum += valueInB.sum;
+                valueInA.max = Math.max(valueInA.max, valueInB.max);
+                valueInA.count += valueInB.count;
+            }
+        }
+
+        return a;
+    }
+
+    protected static class Results extends TreeMap<String, CityData> {
+
+    }
+
+    protected static class CityData {
+        int min, sum, max, count;
+
+        public CityData(int min, int sum, int max, int count) {
+            this.min = min;
+            this.sum = sum;
+            this.max = max;
+            this.count = count;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o)
+                return true;
+            if (o == null || getClass() != o.getClass())
+                return false;
+            CityData cityData = (CityData) o;
+            return min == cityData.min && sum == cityData.sum && max == cityData.max && count == cityData.count;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(min, sum, max, count);
+        }
+
+        @Override
+        public String toString() {
+            return STR."CityData{min=\{min}, sum=\{sum}, max=\{max}, count=\{count}\{'}'}";
+        }
+    }
+
+    protected static void printCities(Results cities) {
+        System.out.print("{");
+        for (String city : cities.keySet()) {
+            CityData data = cities.get(city);
+            var min = data.min / 10.0;
+            var mean = (data.sum * 10.0 / data.count) / 100.0;
+            var max = data.max / 10.0;
+            System.out.printf(
+                    "%s=%.1f/%.1f/%.1f, ",
+                    city,
+                    min,
+                    mean,
+                    max);
+        }
+        System.out.print("}");
+    }
+}