MahmoudFawzyKhalil's implementation (#438)

* Initial commit trying out multiple things

* Clean up code

* Fix rounding error to fix failing test

calculate_average_MahmoudFawzyKhalil.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_MahmoudFawzyKhalil

src/main/java/dev/morling/onebrc/CalculateAverage_MahmoudFawzyKhalil.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.lang.foreign.Arena;
+import java.lang.foreign.MemorySegment;
+import java.lang.foreign.ValueLayout;
+import java.nio.channels.FileChannel;
+import java.util.*;
+import java.util.concurrent.ForkJoinPool;
+
+// Solution using project Panama and Map Reduce
+public class CalculateAverage_MahmoudFawzyKhalil {
+
+    private static final String FILE = "./measurements.txt";
+
+    public static void main(String[] args) throws Exception {
+        mapReduce();
+    }
+
+    private static void mapReduce() throws IOException {
+        var f = new File(FILE);
+        try (var raf = new RandomAccessFile(f, "r")) {
+            FileChannel channel = raf.getChannel();
+            long fileSize = channel.size();
+            MemorySegment ms = channel.map(FileChannel.MapMode.READ_ONLY, 0, fileSize, Arena.global());
+            long chunkSize = fileSize / ForkJoinPool.commonPool().getParallelism();
+            List<Chunk> chunks = getChunks(ms, chunkSize);
+            Map<String, MeasurementAggregate> result = chunks.stream()
+                    .parallel()
+                    .map(c -> readChunkToMap(c, ms))
+                    .reduce(Collections.emptyMap(), (a, b) -> combine(a, b));
+            System.out.println(new TreeMap<>(result));
+        }
+    }
+
+    private static List<Chunk> getChunks(MemorySegment ms, long chunkSize) {
+        List<Chunk> chunks = new ArrayList<>(32);
+        long start = 0;
+        long fileSize = ms.byteSize();
+        long end = chunkSize;
+
+        while (start < fileSize) {
+            byte b = ms.get(ValueLayout.JAVA_BYTE, end);
+            if (b == '\n') {
+                chunks.add(new Chunk(start, end));
+                start = end + 1;
+                end = Math.min(end + chunkSize, fileSize - 2);
+            }
+            end++;
+        }
+        return chunks;
+    }
+
+    private static Map<String, MeasurementAggregate> readChunkToMap(Chunk chunk, MemorySegment ms) {
+        Map<String, MeasurementAggregate> map = new HashMap<>();
+
+        long start = chunk.start();
+        while (start < chunk.end()) {
+            long cityNameSize = 0;
+            while (ms.get(ValueLayout.JAVA_BYTE, start + cityNameSize) != ';') {
+                cityNameSize++;
+            }
+
+            String cityName = readString(ms, start, cityNameSize);
+            start = start + cityNameSize + 1;
+
+            long temperatureSize = 0;
+            while (ms.get(ValueLayout.JAVA_BYTE, start + temperatureSize) != '\n') {
+                temperatureSize++;
+            }
+
+            String temperature = readString(ms, start, temperatureSize);
+            start = start + temperatureSize + 1;
+
+            // System.out.println(STR."\{cityName};\{temperature}");
+            addMeasurement(map, cityName, temperature);
+        }
+
+        return map;
+    }
+
+    // Credit goes to imrafaelmerino for combine function
+    private static Map<String, MeasurementAggregate> combine(Map<String, MeasurementAggregate> xs, Map<String, MeasurementAggregate> ys) {
+        Map<String, MeasurementAggregate> result = new HashMap<>();
+
+        for (var key : xs.keySet()) {
+            var m1 = xs.get(key);
+            var m2 = ys.get(key);
+            var combined = (m2 == null) ? m1 : (m1 == null) ? m2 : m1.combine(m2);
+            result.put(key, combined);
+        }
+
+        for (var key : ys.keySet())
+            result.putIfAbsent(key, ys.get(key));
+        return result;
+    }
+
+    private static String readString(MemorySegment ms, long start, long size) {
+        byte[] stringBytes = ms.asSlice(start, size)
+                .toArray(ValueLayout.JAVA_BYTE);
+        return new String(stringBytes);
+    }
+
+    private static void addMeasurement(Map<String, MeasurementAggregate> measurements, String station, String reading) {
+        measurements.compute(station,
+                (_, oldMeasurements) -> oldMeasurements == null ? MeasurementAggregate.of(reading) : oldMeasurements.update(reading));
+    }
+
+    record Chunk(long start, long end) {
+    }
+
+    private static final class MeasurementAggregate {
+        private double min;
+        private double max;
+        private double sum;
+        private long count;
+
+        private MeasurementAggregate(double min, double max, double sum, long count) {
+            this.min = min;
+            this.max = max;
+            this.sum = sum;
+            this.count = count;
+        }
+
+        public static MeasurementAggregate of(String temperature) {
+            double measurement = Double.parseDouble(temperature);
+            return new MeasurementAggregate(measurement, measurement, measurement, 1);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj == this)
+                return true;
+            if (obj == null || obj.getClass() != this.getClass())
+                return false;
+            var that = (MeasurementAggregate) obj;
+            return Double.doubleToLongBits(this.min) == Double.doubleToLongBits(that.min) &&
+                    Double.doubleToLongBits(this.max) == Double.doubleToLongBits(that.max) &&
+                    Double.doubleToLongBits(this.sum) == Double.doubleToLongBits(that.sum) &&
+                    this.count == that.count;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(min, max, sum, count);
+        }
+
+        public MeasurementAggregate update(String part) {
+            double measurement = Double.parseDouble(part);
+            this.min = Math.min(this.min, measurement);
+            this.max = Math.max(this.max, measurement);
+            this.sum += measurement;
+            this.count++;
+            return this;
+        }
+
+        public String toString() {
+            return min + "/" + round(round(sum) / count) + "/" + max;
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+
+        public MeasurementAggregate combine(MeasurementAggregate m2) {
+            return new MeasurementAggregate(
+                    Math.min(this.min, m2.min),
+                    Math.max(this.max, m2.max),
+                    this.sum + m2.sum,
+                    this.count + m2.count);
+        }
+    }
+}