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26. ForkJoin:单机版的MapReduce - 并发工具类
阅读量:386 次
发布时间:2019-03-05

本文共 2510 字,大约阅读时间需要 8 分钟。

???????ForkJoin??

??????

????????????????????????????????????????????????????????????????????????????

  • ??????????????????????????????????????
  • ??????????????????????????????
  • Fork/Join???

    Fork/Join???Java???????????????????????????????????????

    • Fork?????????fork()????????????????????
    • Join?????????join()?????????????????

    ForkJoin?????????????

  • ForkJoinPool????????????????ForkJoin???????????????????????????
  • ForkJoinTask???????????????????????????
    • fork()??????????
    • join()??????????????
  • ForkJoinTask????????

  • RecursiveAction?????????????????????????
  • RecursiveTask????????????????????????
  • ForkJoinPool????

    ForkJoinPool??????????-???????????????????????ForkJoinPool????????????????????????????????????????????????????????????????

    ForkJoinPool??????????????????????????????????

    ??MapReduce??????

    MapReduce???????????????????????????MapReduce??????????

    public class MyTest2 {
    public static void main(String[] args) {
    String[] fc = {
    "hello world", "hello me", "hello fork", "hello join",
    "fork join in world"
    };
    ForkJoinPool fjp = new ForkJoinPool(3);
    MR mr = new MR(fc, 0, fc.length);
    Map
    result = fjp.invoke(mr);
    result.forEach((k, v) -> System.out.println(k + ":" + v));
    }
    static class MR extends RecursiveTask
    > {
    private String[] fc;
    private int start, end;
    MR(String[] fc, int fr, int to) {
    this.fc = fc;
    this.start = fr;
    this.end = to;
    }
    @Override
    protected Map
    compute() {
    if (end - start == 1) {
    return calc(fc[start]);
    } else {
    int mid = (start + end) / 2;
    MR mr1 = new MR(fc, start, mid);
    mr1.fork();
    MR mr2 = new MR(fc, mid, end);
    return merge(mr2.compute(), mr1.join());
    }
    }
    private Map
    merge(Map
    r1, Map
    r2) { Map
    result = new HashMap<>(); result.putAll(r1); r2.forEach((k, v) -> { Long c = result.get(k); if (c != null) { result.put(k, c + v); } else { result.put(k, v); } }); return result; } private Map
    calc(String line) { Map
    result = new HashMap<>(); String[] words = line.split("\\s+"); for (String w : words) { Long v = result.get(w); if (v != null) { result.put(w, v + 1L); } else { result.put(w, 1L); } } return result; } } }

    ??????MR???????????????????????ForkJoin?????????????????????????????????

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