Implementation by rprabhu

Co-authored-by: Prabhu R <prabhu.rengaswamy@outlook.com>

calculate_average_rprabhu.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=""
+time java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_rprabhu

src/main/java/dev/morling/onebrc/CalculateAverage_rprabhu.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.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.TreeMap;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class CalculateAverage_rprabhu {
+
+    private static final String FILE = "./measurements.txt";
+
+    private static record Measurement(String station, double value) {
+        private Measurement(String[] parts) {
+            this(parts[0], Double.parseDouble(parts[1]));
+        }
+    }
+
+    private static record ResultRow(double min, double mean, double max) {
+        public String toString() {
+            return round(min) + "/" + round(mean) + "/" + round(max);
+        }
+
+        private double round(double value) {
+            return Math.round(value * 10.0) / 10.0;
+        }
+    };
+
+    private static class MeasurementAggregator {
+        private double min = Double.POSITIVE_INFINITY;
+        private double max = Double.NEGATIVE_INFINITY;
+        private double sum;
+        private long count;
+    }
+
+    private static ConcurrentHashMap<String, MeasurementAggregator> map = new ConcurrentHashMap<>();
+
+    private static final int TASK_CHUNK = 50000;
+
+    private static class TaskExecutor implements Runnable {
+        List<String> list;
+
+        TaskExecutor(List<String> list) {
+            this.list = list;
+        }
+
+        @Override
+        public void run() {
+            for (String str : list) {
+                // System.out.println(str);
+                // String[] values = str.split(";");
+                int index = str.indexOf(';');
+                String station = str.substring(0, index);
+                double val = Double.parseDouble(str.substring(index + 1));
+                // double val = Double.parseDouble(values[1]);
+                MeasurementAggregator aggr = map.getOrDefault(station, new MeasurementAggregator());
+                aggr.count += 1;
+                aggr.sum += val;
+                aggr.max = (val >= aggr.max) ? val : aggr.max; // Math.max(aggr.max, val);
+                aggr.min = (val <= aggr.min) ? val : aggr.min; // Math.min(aggr.min, val);
+                map.put(station, aggr);
+            }
+
+        }
+
+    }
+
+    private static class TaskScheduler {
+        ExecutorService executor;
+        List<String> list = new ArrayList<>(TASK_CHUNK);
+
+        TaskScheduler(ExecutorService executor) {
+            this.executor = executor;
+        }
+
+        void push(String line) {
+            // System.out.println("adding: " + line);
+            list.add(line);
+            if (list.size() >= TASK_CHUNK) {
+                executor.submit(new TaskExecutor(list));
+                list = new ArrayList<>(TASK_CHUNK);
+            }
+        }
+
+        void completeRemaining() {
+            // System.out.println("Completing remaining: " + list.size());
+            if (!list.isEmpty()) {
+                // System.out.println("Scheduling remaining");
+                executor.submit(new TaskExecutor(list));
+            }
+        }
+
+    }
+
+    public static void main(String[] args) throws IOException, InterruptedException, ExecutionException {
+
+        // ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
+        // ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
+        ExecutorService executor = Executors.newCachedThreadPool();
+        TaskScheduler scheduler = new TaskScheduler(executor);
+        Files.lines(Paths.get(FILE), StandardCharsets.UTF_8).forEach(line -> {
+            scheduler.push(line);
+        });
+        scheduler.completeRemaining();
+        executor.shutdown();
+        executor.awaitTermination(600, TimeUnit.SECONDS);
+
+        Map<String, ResultRow> sortedResult = new TreeMap<>();
+        map.forEach(
+                (key, value) -> sortedResult.put(key, new ResultRow(value.min, value.sum / value.count, value.max)));
+        System.out.println(sortedResult);
+
+    }
+}