java-forkjoin帶有傳回值

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來自並發編程網: http://ifeve.com/fork-join-3/

如果這個任務必須解決一個超過預定義大小的問題，你應該將這個任務分解成更多的子任務，並且用Fork/Join架構來執行這些子任務。當這些子任務完成執行，發起的任務將獲得所有子任務產生的結果 ，對這些結果進行分組，並返回最終的結果。最終，當在池中執行的發起的任務完成它的執行，你將擷取整個問題地最終結果。

1, 產生二維數組類比文檔: 

package com.wenbronk.forkjoin.withresult;import java.util.Random;/** * Created by wenbronk on 2017/7/26. */public class Document {    private String words[] = {"the", "hello", "goodbye", "pack", "java", "thread", "pool", "random", "class", "main"};    public String[][] generateDocument(int numLines, int numWords, String word) {        int counter = 0;        String[][] document = new String[numLines][numWords];        Random random = new Random();        // 填充數組        for (int i=0; i<numLines; i++){            for (int j=0; j<numWords; j++) {                int index=random.nextInt(words.length);                document[i][j]=words[index];                if (document[i][j].equals(word)){                    counter++;                }            }        }        System.out.println(document.length + ": " + document[document.length - 1].length);        System.out.println("DocumentMock: The word appears " + counter + " times in the document");        return document;    }}

2, 對類比文檔的進行行拆分

package com.wenbronk.forkjoin.withresult;import java.util.ArrayList;import java.util.concurrent.ExecutionException;import java.util.concurrent.RecursiveTask;/** * Created by wenbronk on 2017/7/26. */public class DocumentTask extends RecursiveTask<Integer> {    private String[][] document;    private int start, end;    private String word;    public DocumentTask(String[][] document, int start, int end, String word) {        this.document = document;        this.start = start;        this.end = end;        this.word = word;    }    @Override    protected Integer compute() {        int result = 0;        if (end - start < 10) {            result = processLines(document, start, end, word);        } else {            int mid = (start + end) / 2;            DocumentTask task1 = new DocumentTask(document, start, mid, word);            DocumentTask task2 = new DocumentTask(document, mid, end, word);            invokeAll(task1, task2);            try {                result = groupResults(task1.get(), task2.get());            }catch (InterruptedException | ExecutionException e) {                e.printStackTrace();            }        }        return result;    }    private int groupResults(Integer integer, Integer integer1) {        return integer + integer1;    }    /**     * 要尋找的單詞     */    private int processLines(String[][] document, int start, int end, String word) {        ArrayList<LineTask> tasks = new ArrayList<>();        for (int i = start; i < end; i++) {            LineTask lineTask = new LineTask(document[i], 0, document[i].length, word);            tasks.add(lineTask);        }        invokeAll(tasks);        int result = 0;//        for (LineTask task : tasks) {        for (int i = 0; i < tasks.size(); i++) {            LineTask task = tasks.get(i);            try {//                Thread.sleep(100);                result += task.get();            } catch (Exception e) {                e.printStackTrace();            }        }        return result;    }}

3, 對行進行單詞拆分

package com.wenbronk.forkjoin.withresult;import java.util.concurrent.RecursiveTask;/** * 統計單詞在一行出現的次數 * Created by wenbronk on 2017/7/27. */public class LineTask extends RecursiveTask<Integer> {    private static final long seriaVersionUID = 1L;    private String[] line;    private int start, end;    private String word;    public LineTask(String[] line, int start, int end, String word) {        this.line = line;        this.start = start;        this.end = end;        this.word = word;    }    @Override    protected Integer compute() {        Integer result = null;        if (end - start < 100) {            result = count(line, start, end, word);        }else {            int mid = (start + end) / 2;            LineTask task1 = new LineTask(line, start, mid, word);            LineTask task2 = new LineTask(line, mid, end, word);            invokeAll(task1, task2);            try {                result = groupResult(task1.get(), task2.get());            } catch (Exception e) {                e.printStackTrace();            }        }        return result;    }    /**     * 合并2個數值的值, 返回結果     * @return     */    private Integer groupResult(Integer num1, Integer num2) {        return num1 + num2;    }    /**     * 尋找行中出現word的次數     */    private Integer count(String[] line, int start, int end, String word) {        int counter = 0;        for (int i = start; i < end; i++) {            if (word.equals(line[i])) {                counter ++;            }        }//        try {//            Thread.sleep(10);//        } catch (Exception e) {//            e.printStackTrace();//        }        return counter;    }}

4, 入口執行類

package com.wenbronk.forkjoin.withresult;import java.util.concurrent.ForkJoinPool;import java.util.concurrent.TimeUnit;/** * Created by wenbronk on 2017/7/27. */public class CountMain {    public static void main(String[] args) {        Document document = new Document();        String[][] documents = document.generateDocument(100, 1000, "random");        DocumentTask task = new DocumentTask(documents, 0, 100, "random");        ForkJoinPool pool = new ForkJoinPool();        pool.execute(task);        do {            System.out.printf("******************************************\n");            System.out.printf("Main: Parallelism: %d\n",pool.getParallelism());            System.out.printf("Main: Active Threads: %d\n",pool.getActiveThreadCount());            System.out.printf("Main: Task Count: %d\n",pool.getQueuedTaskCount());            System.out.printf("Main: Steal Count: %d\n",pool.getStealCount());            System.out.printf("******************************************\n");            try {                TimeUnit.SECONDS.sleep(1);            } catch (InterruptedException e) {                e.printStackTrace();            }        } while (!task.isDone());        pool.shutdown();        try {            System.out.printf("Main: The word appears %d in the document ", task.get());        } catch (Exception e) {            e.printStackTrace();        }    }}

 

java-forkjoin帶有傳回值