Java Fork Join Forkjoinpool Usage Example

This example is to decompose a large array of sums of large tasks into small tasks that are summed in small areas, and then add together these small tasks to the result.

Technology: JDK8.0, Recursivetask technology in Java fork-join mode, override Compute ().

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2. /**
4. * Author:bigtree
6. * This example is the large task of summing up a large array into small tasks that sum in small sums, and then adding up the sum of these small tasks is the result of the calculation.
8. Technology
10. * Recursivetask technology in Java fork-join mode, override Compute ().
12. */
16. Import java.util.*;
18. Import java.util.concurrent.*;
20. Class Caltask extends recursivetask<long>{
22. private static final int THRESHOLD = 1000; //how Many numbers one thread can calculate
24. private long data[];
26. private int start;
28. private int end;
32. Public Caltask (long[] inputdata,int start, int end) {
34. Data=inputdata;
36. This.start=start;
38. This.end=end;
40. }
42. @Override
44. protected Long Compute () {
46. Long sumresult=0l;
48. if ((End-start) <= THRESHOLD) {
50. For (int index=start; index<end;index++) {
52. Sumresult + = Data[index];
54. }
56. }
58. else { //parallel computing
60. int step= (end-start)/threshold;
62. if (((End-start)%threshold) >0)
64. step+=1;
66. arraylist<caltask> tasks = new arraylist<> ();
68. int Pos=start;
70. int lastposition;
72. For (int i=0;i<step;i++) {
74. Lastposition=pos+threshold;
76. if (lastposition>end)
78. Lastposition=end;
80. Caltask onetask= New Caltask (data,pos,lastposition);
82. Pos=lastposition;
84. Tasks.add (OneTask);
86. Onetask.fork ();
88. }
90. For (Caltask mtask:tasks) {
92. Sumresult + = Mtask.join ();
94. }
96. }
98. return sumresult;
100. }
102. }
106. public class Forkjoincompute {
108. public static void Forkjoinshow () {
110. long data[] = new long[20001];
112. For (long i=0;i<data.length;i++) {
114. data[(int) i]= i + 1;
116. }
118. Forkjoinpool mypool= Forkjoinpool.commonpool ();
120. future<long> myfuture = Mypool.submit ( new Caltask (data,0,data.length));
122. try{
124. long Result=myfuture.get ();
126. System.out.println ("Forkjoincompute (): Computed final result=" +result);
128. } catch (Interruptedexception e) {
130. E.printstacktrace ();
132. } catch (Executionexception e) {
134. //TODO auto-generated catch block
136. E.printstacktrace ();
138. }
140. Mypool.shutdown ();
142. }
144. }

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Output Result:

Forkjoincompute (): Computed final result=200030001

Java Fork Join Forkjoinpool Usage Example