Fork/Join是一种基于“分治”的算法:分解任务+合并结果。
ForkJoinPool线程池可以把一个大任务分拆成小任务并行执行。
任务类必须继承自RecursiveTask/RecursiveAction。
使用Fork/Join模式可以进行并行计算提高效率。
package com.feiyangedu.sample; import java.util.Random; import java.util.concurrent.ForkJoinPool; import java.util.concurrent.ForkJoinTask; import java.util.concurrent.RecursiveTask; class SumTask extends RecursiveTask<Long> { private static final long serialVersionUID = 1L; static final int THRESHOLD = 500; long[] array; int start; int end; SumTask(long[] array, int start, int end) { this.array = array; this.start = start; this.end = end; } @Override protected Long compute() { if (end - start <= THRESHOLD) { // 如果任务足够小,直接计算: long sum = 0; for (int i = start; i < end; i++) { sum += this.array[i]; try { Thread.sleep(2); } catch (InterruptedException e) { e.getStackTrace(); } } return sum; } // 任务太大,一分为二: int middle = (end + start) / 2; System.out.println(String.format("split %d~%d ==> %d~%d, %d~%d", start, end, start, middle, middle, end)); SumTask subtask1 = new SumTask(this.array, start, middle); SumTask subtask2 = new SumTask(this.array, middle, end); invokeAll(subtask1, subtask2); Long subresult1 = subtask1.join(); Long subresult2 = subtask2.join(); Long result = subresult1 + subresult2; System.out.println("result = " + subresult1 + " + " + subresult2 + " ==> " + result); return result; } } public class ForkJoinTaskSample { public static void main(String[] args) throws Exception { // 创建1000个随机数组成的数组: long[] array = new long[1000]; long expectedSum = 0; for (int i = 0; i < array.length; i++) { array[i] = random(); expectedSum += array[i]; } System.out.println("Expected sum: " + expectedSum); // fork/join: ForkJoinTask<Long> task = new SumTask(array, 0, array.length); long startTime = System.currentTimeMillis(); Long result = ForkJoinPool.commonPool().invoke(task); long endTime = System.currentTimeMillis(); System.out.println("Fork/join sum: " + result + " in " + (endTime - startTime) + " ms."); } static Random random = new Random(0); static long random() { return random.nextInt(10000); } }