[investigation] possible load optimization: use Seekable/Parallel reading

[sszuev]

In case the serialization format (lang) is not provided we have to iterate all supported formats to find the best suitable.
This peace of code can be optimized using file rewinding or parallel running.
To compare:

Standard sequence reading

    private static void loadStd(Path p, int n, long lines) throws IOException {
        int step = n / 100;
        for (int i = 0; i < n; i++) {
            if (i % step == 0) {
                System.out.print("#");
            }
            try (BufferedReader r = Files.newBufferedReader(p)) {
                if (lines != r.lines().count()) {
                    throw new IllegalStateException();
                }
            }
        }
        System.out.println();
    }

vs SeekableByteChannel reading

    private static void loadNio(Path p, int n, long lines) throws IOException {
        int step = n / 100;
        try (SeekableByteChannel chanel = Files.newByteChannel(p, StandardOpenOption.READ)) {
            for (int i = 0; i < n; i++) {
                if (i % step == 0) {
                    System.out.print("#");
                }
                BufferedReader r = new BufferedReader(Channels.newReader(chanel, StandardCharsets.UTF_8));
                if (lines != r.lines().count()) {
                    throw new IllegalStateException();
                }
                chanel.position(0);
            }
        }
        System.out.println();
    }

vs concurrent reading

    private static void loadParallel(Path p, int n, long lines) throws ExecutionException, InterruptedException {
        System.out.println("Go");
        ExecutorService service = Executors.newWorkStealingPool();
        CompletableFuture<?>[] futures = IntStream.range(0, n).mapToObj(x -> CompletableFuture.runAsync(() -> {
            try (BufferedReader r = Files.newBufferedReader(p)) {
                if (lines != r.lines().count()) {
                    throw new IllegalStateException();
                }
                System.out.println(Thread.currentThread() + " is done.");
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }, service)).toArray(CompletableFuture[]::new);
        CompletableFuture.allOf(futures).get();
        System.out.println("Done");
    }