Counting the size of a directory

JavaDU.java

import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.LinkOption;
import java.nio.file.Paths;
import java.util.List;
import java.util.ArrayList;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;
import java.io.IOException;

public class JavaDU {

    public static class CountingTask extends RecursiveTask<Long> {
        private Path dir;
     
        public CountingTask(Path dir) {
            this.dir = dir;
        }
     
        @Override
        protected Long compute() {
            long size = 0;
            List<CountingTask> subTasks = new ArrayList<CountingTask>();

            try (DirectoryStream<Path> ds = Files.newDirectoryStream(dir)) {
                for (Path subPath : ds) {
                    if (Files.isDirectory(subPath, LinkOption.NOFOLLOW_LINKS)) {
                        subTasks.add(new CountingTask(subPath));
                    } else {
                        long s = Files.size(subPath);
                        // System.out.println(s + "\t" + subPath);
                        size += s;
                    }
                }
     
                if (!subTasks.isEmpty()) {
                    for (CountingTask subTask : invokeAll(subTasks)) {
                        long s = subTask.join();
                        // System.out.println(s + "\t" + subTask.dir);
                        size += s;
                    }
                }

            } catch (IOException ex) {
                // ex.printStackTrace();
                return 0L;
            }
            return size;
        }
    }

    public static void main(String[] args) {
        int parallelism = Runtime.getRuntime().availableProcessors() << 1;
        Long size = new ForkJoinPool(parallelism).invoke(
                            new CountingTask(Paths.get(args[0])));
        System.out.println(size + "\t" + args[0]);
        System.out.println(size + "\ttotal");
    }
    
}

不错，fork/join解决了划分出来的任务在线程间均匀分配的问题。