Memory mapped buffers, ints instead of floats and epsilon GC (#451)

* Modify baseline version to improve performance

- Consume and process stream in parallel with memory map buffers, parsing it directly
- Use int instead of float/double to store values
- Use Epsilon GC and graal

* Update src/main/java/dev/morling/onebrc/CalculateAverage_adriacabeza.java

* Update calculate_average_adriacabeza.sh

---------

Co-authored-by: Gunnar Morling <gunnar.morling@googlemail.com>

calculate_average_adriacabeza.sh

@@ -0,0 +1,22 @@
+#!/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.
+#
+# sdk use java 21.0.1-graal 1>&2
+
+
+JAVA_OPTS="-XX:+UseStringDeduplication -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC"
+java --enable-preview  -classpath target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_adriacabeza
+

prepare_adriacabeza.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+#
+#  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.
+#
+
+source "$HOME/.sdkman/bin/sdkman-init.sh"
+sdk use java 21.0.1-graal 1>&2

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

@@ -0,0 +1,223 @@
+/*
+ *  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.MappedByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * This class calculates average measurements from a file in a parallelized manner.
+ */
+public class CalculateAverage_adriacabeza {
+
+    private static final Path FILE_PATH = Paths.get("./measurements.txt");
+    public static final int CITY_NAME_MAX_CHARACTERS = 128;
+
+    /**
+     * Represents result containing a HashMap with city as key and ResultRow as value.
+     */
+    private static class Result {
+        private static class StationData {
+            private int min, sum, count, max;
+
+            public StationData(int value) {
+                this.count = 1;
+                this.sum = value;
+                this.min = value;
+                this.max = value;
+            }
+
+            public void update(int value) {
+                this.count++;
+                this.sum += value;
+                this.min = Math.min(this.min, value);
+                this.max = Math.max(this.max, value);
+            }
+
+            public String toString() {
+                return "%.1f/%.1f/%.1f".formatted(min / 10.0, sum / 10.0 / count, max / 10.0);
+            }
+
+        }
+        private final Map<String, StationData> resultMap;
+
+        public Result() {
+            this.resultMap = new HashMap<>();
+        }
+
+        public Map<String, StationData> getResultMap() {
+            return resultMap;
+        }
+
+        public void addMeasurement(String city, int value) {
+            resultMap.compute(city, (_, resultRow) -> {
+                if (resultRow == null) {
+                    return new StationData(value);
+                } else {
+                    resultRow.update(value);
+                    return resultRow;
+                }
+            });
+        }
+
+        public void merge(Result other) {
+            other.getResultMap().forEach((city, resultRow) ->
+                    resultMap.merge(city, resultRow, (existing, incoming) -> {
+                        existing.min = Math.min(existing.min, incoming.min);
+                        existing.max = Math.max(existing.max, incoming.max);
+                        existing.sum += incoming.sum;
+                        existing.count += incoming.count;
+                        return existing;
+                    }));
+        }
+
+        public String toString() {
+            return this.resultMap.entrySet().stream()
+                    .sorted(Map.Entry.comparingByKey())
+                    .map(entry -> "%s=%s".formatted(entry.getKey(), entry.getValue()))
+                    .collect(Collectors.joining(", ", "{", "}"));
+        }
+    }
+
+    /**
+     * Finds the ending position in the file, ensuring it ends at the beginning of a line.
+     *
+     * @param channel  File channel
+     * @param position Current position in the file
+     * @return Ending position at the beginning of a line
+     * @throws IOException If an I/O error occurs
+     */
+    private static long findEndPosition(FileChannel channel, long position) throws IOException {
+        ByteBuffer buffer = ByteBuffer.allocate(1);
+
+        // Iterate over the file from the given position to find the next newline character
+        while (position < channel.size()) {
+            channel.read(buffer, position);
+
+            // Check if the current byte is a newline character
+            if (buffer.get(0) == '\n') {
+                return position + 1; // Return the position immediately after the newline
+            }
+
+            position++;
+            buffer.clear();
+        }
+
+        return channel.size(); // Return the end of the file if no newline is found after the current position
+    }
+
+
+    /**
+     * Gets the mapped byte buffers for parallel processing.
+     *
+     * @param nProcessors Number of processors for parallelization
+     * @return List of MappedByteBuffers
+     * @throws IOException If an I/O error occurs
+     */
+    private static List<MappedByteBuffer> getMappedByteBuffers(int nProcessors) throws IOException {
+        try (FileChannel channel = FileChannel.open(FILE_PATH, StandardOpenOption.READ)) {
+            long fileSize = channel.size();
+            long chunkSize = (fileSize + nProcessors - 1) / nProcessors;
+            long pos = 0;
+
+            List<MappedByteBuffer> buffers = new ArrayList<>(nProcessors);
+            for (int i = 0; i < nProcessors; i++) {
+                long endPosition = findEndPosition(channel, pos + chunkSize);
+                long size = endPosition - pos;
+                MappedByteBuffer buffer = channel.map(FileChannel.MapMode.READ_ONLY, pos, size);
+                pos = pos + size;
+                buffers.add(buffer);
+            }
+            return buffers;
+        }
+    }
+
+    /**
+     * Calculates average measurements from the file.
+     *
+     * @return Result containing min/mean/max values for each city
+     */
+    private static Result calculateAverageMeasurements(List<MappedByteBuffer> chunks) {
+        // Process each buffer in parallel
+        return chunks.parallelStream()
+                .map(buffer -> {
+                    Result partialResult = new Result();
+                    var limit = buffer.limit();
+                    var field = new byte[CITY_NAME_MAX_CHARACTERS];
+                    while (buffer.position() < limit) {
+                        var fieldCurrentIndex = 0;
+                        field[fieldCurrentIndex++] = buffer.get();
+                        while (buffer.position() < limit) {
+                            var fieldByte = buffer.get();
+                            if (fieldByte == ';')
+                                break;
+                            field[fieldCurrentIndex++] = fieldByte;
+                        }
+                        var fieldStr = new String(field, 0, fieldCurrentIndex);
+                        var number = 0;
+                        var sign = 1;
+                        while (buffer.position() < limit) {
+                            var numberByte = buffer.get();
+                            if (numberByte == '-')
+                                sign = -1;
+                            else if (numberByte == '\n')
+                                break;
+                            else if (numberByte != '.')
+                                number = number * 10 + (numberByte - '0');
+                        }
+                        partialResult.addMeasurement(fieldStr, sign * number);
+                    }
+                    return partialResult;
+                }).reduce(new Result(), (partialResult1, partialResult2) -> {
+                    Result result = new Result();
+                    result.merge(partialResult1);
+                    result.merge(partialResult2);
+                    return result;
+                });
+    }
+
+    /**
+     * The main method to run the average measurements calculations program.
+     *
+     * @param args Command line arguments. Not utilized in this program.
+     */
+    public static void main(String[] args) {
+        try {
+            // Get the MappedByteBuffers by splitting the file evenly across available processors
+            var buffers = getMappedByteBuffers(Runtime.getRuntime().availableProcessors());
+
+            // Calculate the average measurements from the buffers obtained
+            var measurements = calculateAverageMeasurements(buffers);
+
+            // Print the measurements result to the console.
+            System.out.println(measurements);
+
+        } catch (IOException e) {
+            // Handle any potential I/O exceptions by printing the error message to the console
+            System.err.println(STR."Error processing file: \{e.getMessage()}");
+        }
+    }
+}