26. ForkJoin：单机版的MapReduce - 并发工具类-白红宇

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; } } }