Another implementation for fast file reading

sol.java

private static void readFile() throws IOException {
    List<StartEndRecord> records = new ArrayList<>();
    long numberOfChunks = 3l;
    try (RandomAccessFile file = new RandomAccessFile(TEST_FILE_PATH, "r")) {
        FileChannel channel = file.getChannel();
        long fileSize = channel.size();
        MemorySegment map = channel.map(FileChannel.MapMode.READ_ONLY, 0, fileSize, Arena.global());

        long start = 0;
        long chunkSize = fileSize / numberOfChunks;

        for (long i = 0; i < numberOfChunks; i++) {
            long endCandidate = start + chunkSize;
            while (endCandidate < fileSize && map.get(ValueLayout.JAVA_BYTE, endCandidate) != '\n') {
                endCandidate++;
            }
            records.add(new StartEndRecord(start, Math.min(endCandidate, fileSize)));
            start = Math.min(endCandidate, fileSize);
        }

        Map<String, DoubleSummaryStatistics> stringDoubleSummaryStatisticsMap = processFile((int) numberOfChunks, records, map);
        System.out.println(stringDoubleSummaryStatisticsMap);
    }
}

private static Map<String, DoubleSummaryStatistics> processFile (int numChunks, List<StartEndRecord> records, MemorySegment map) {
    Map<String, DoubleSummaryStatistics> valueMap = new HashMap<>();
    try (ExecutorService service = Executors.newFixedThreadPool(numChunks)) {
        records.parallelStream().forEach(r -> {
            service.execute(() -> {
                long chunkStart = r.chunkStart;
                long chunkEnd = r.chunkEnd;
                long index = chunkStart;
                String name = "";
                String number = "";
                // TODO: for the reader, this could and should be extracted to another method
                while (index < chunkEnd) {
                    char currentChar = (char)map.get(ValueLayout.JAVA_BYTE, index);
                    while (currentChar != ';' && index < chunkEnd) {
                        name += currentChar;
                        index++;
                        currentChar = (char)map.get(ValueLayout.JAVA_BYTE, index);
                    }
                    index++;
                    if (index >= chunkEnd) {
                        break;
                    }
                    currentChar = (char)map.get(ValueLayout.JAVA_BYTE, index);

                    while (currentChar != '\n') {
                        number += currentChar;
                        index++;
                        if (index >= chunkEnd) {
                            break;
                        }
                        currentChar = (char)map.get(ValueLayout.JAVA_BYTE, index);
                    }

                    double d = Double.parseDouble(number);
                    DoubleSummaryStatistics stats = valueMap.containsKey(name) ? valueMap.get(name) : new DoubleSummaryStatistics();
                    if (valueMap.containsKey(name)) {
                        stats.accept(d);
                    } else {
                        stats.accept(d);
                    }
                    stats.accept(d);
                    valueMap.put(name, stats);
                    name = "";
                    number = "";
                }
            });
        });
        try {
            service.shutdown();
            while (!service.awaitTermination(3, TimeUnit.MINUTES)) {
                System.out.println("Not terminated yet");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return valueMap;
    }
}