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

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???????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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