本例是把一個大的數組求和的計算的大任務分解到在小范圍內求和的小任務，然后把這些小任務之和加起來就是所求之結果。

?技術：JDK8.0,?Java fork-join模式下的RecursiveTask技術，override compute().?

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1. /**?
2. ?*?Author:?Bigtree?
3. ?*?本例是把一個大的數組求和的計算的大任務分解到在小范圍內求和的小任務，然后把這些小任務之和加起來就是所求之結果。?
4. ?*?技術：?
5. ?*?java?fork-join模式下的RecursiveTask技術，override?compute().??
6. ?*/??
7. ??
8. import?java.util.*;??
9. import?java.util.concurrent.*;??
10. class?Caltask?extends?RecursiveTask<Long>{??
11. ????private?static?final?int?THRESHOLD?=?1000;?//how?many?numbers?one?thread?can?calculate??
12. ????private?long?data[];??
13. ????private?int?start;??
14. ????private?int?end;??
15. ??????
16. ????public?Caltask(long[]?inputData,int?start,?int?end){??
17. ????????data=inputData;??
18. ????????this.start=start;??
19. ????????this.end=end;??
20. ????}??
21. ????@Override??
22. ????protected?Long?compute()?{??
23. ????????Long?sumResult=0L;??
24. ????????if((end?-?start)?<=?THRESHOLD?){??
25. ??????????for(int?index=start;?index<end;index++)?{??
26. ??????????????sumResult?+=?data[index];??
27. ???????????}??
28. ?????????}???
29. ????????else?{?//parallel?computing??
30. ????????????int?step=(end-start)/THRESHOLD;??
31. ????????????if(((end-start)%THRESHOLD)>0)??????
32. ????????????????step+=1;??????????????
33. ????????????ArrayList<Caltask>?tasks?=?new?ArrayList<>();??
34. ????????????int?pos=start;??
35. ????????????int?lastposition;?????????????
36. ????????????for(int?i=0;i<step;i++){??
37. ?????????????lastposition=pos+THRESHOLD;????????????????
38. ??????????????if(lastposition>end)???
39. ??????????????????lastposition=end;?????????????
40. ??????????????Caltask?onetask=?new?Caltask(data,pos,lastposition);??
41. ??????????????pos=lastposition;??
42. ??????????????tasks.add(onetask);??
43. ??????????????onetask.fork();??
44. ????????????}?????????????
45. ????????????for(Caltask?mtask?:?tasks){??
46. ????????????????sumResult?+=?mtask.join();????????????????
47. ????????????}??
48. ????????}??
49. ????????return?sumResult;??
50. ????}??
51. ?}??
52. ??
53. ?public?class?forkjoincompute?{??
54. ????public?static?void?ForkJoinShow(){??
55. ????????long?data[]?=?new?long[20001];??
56. ????????for(long?i=0;i<data.length;i++){??
57. ????????????data[(int)?i]=?i?+?1;??
58. ????????}??
59. ????????ForkJoinPool?mypool=?ForkJoinPool.commonPool();??
60. ????????Future<Long>?myfuture?=?mypool.submit(?new?Caltask(data,0,data.length));??
61. ????????try{??
62. ??????????long?result=myfuture.get();??
63. ??????????System.out.println("forkjoincompute():computed?final?result="+result);??
64. ????????}?catch(InterruptedException?e){??
65. ????????????e.printStackTrace();??????????????
66. ????????}?catch?(ExecutionException?e)?{??
67. ????????????//?TODO?Auto-generated?catch?block??
68. ????????????e.printStackTrace();??
69. ????????}?????????
70. ????????mypool.shutdown();????????
71. ????}??
72. }??

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1. ??

輸出結果：

forkjoincompute():computed final result=200030001

轉載于:https://www.cnblogs.com/Free-Thinker/p/6231728.html

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