class SumTask extends RecursiveTask<Long> {static final int THRESHOLD = 100;long[] array;int start;int end;SumTask(long[] array, int start, int end) {this.array = array;this.start = start;this.end = end;}@Overrideprotected 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 += array[i];}try {Thread.sleep(1000);} catch (InterruptedException e) {}System.out.println(String.format("compute %d~%d = %d", start, end, sum));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 static void main(String[] args) throws Exception {// 创建随机数组成的数组:long[] array = new long[400];fillRandom(array);// fork/join task:ForkJoinPool fjp = new ForkJoinPool(4); // 最大并发数4ForkJoinTask<Long> task = new SumTask(array, 0, array.length);long startTime = System.currentTimeMillis();Long result = fjp.invoke(task);long endTime = System.currentTimeMillis();System.out.println("Fork/join sum: " + result + " in " + (endTime - startTime) + " ms.");
}

protected Long compute() {if (任务足够小?) {return computeDirect();}// 任务太大,一分为二:SumTask subtask1 = new SumTask(...);SumTask subtask2 = new SumTask(...);// 分别对子任务调用fork():subtask1.fork();subtask2.fork();// 合并结果:Long subresult1 = subtask1.join();Long subresult2 = subtask2.join();return subresult1 + subresult2;
}

// 分别对子任务调用fork():
subtask1.fork();
subtask2.fork();