Fork/Join框架实现多任务执行计算

骑猪看日落 2022-12-24 00:43 81阅读 0赞

/**
     * 并行计算实现1+2+...+100
     */
    public class CountTask extends RecursiveTask<Integer> {
        public static final int THRESHOLD = 2;
        private int start;
        private int end;
    
        public CountTask(int start, int end) {
            this.start = start;
            this.end = end;
        }
    
        @Override
        protected Integer compute() {
            int sum = 0;
    
            //如果任务足够小，就直接计算任务
            boolean canCompute = (end - start) <= THRESHOLD;
            if (canCompute) {
                for (int i = start; i <= end; i++) {
                    sum += i;
    
                }
            } else {
                //如果任务数量大于阈值，继续分裂成两个子任务
                int middle = (start + end) / 2;
                CountTask leftTask = new CountTask(start, middle);
                CountTask rightTask = new CountTask(middle + 1, end);
                //执行子任务
                leftTask.fork();
                rightTask.fork();
                //等待子任务执行完成，并得到结果
                Integer leftResult = leftTask.join();
                Integer rightResult = rightTask.join();
                //合并子任务
                sum = leftResult + rightResult;
            }
            return sum;
    
        }
    
        public static void main(String[] args) {
            long start = System.currentTimeMillis();
            ForkJoinPool forkJoinPool = new ForkJoinPool();
            CountTask countTask = new CountTask(1, 100);
    
            ForkJoinTask<Integer> result = forkJoinPool.submit(countTask);
    
            try {
                System.out.println(result.get());
                System.out.println(System.currentTimeMillis()-start);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }
        }
    }

> 异常处理

ForkJoinTask任务在执行的时候抛出异常无法直接在主线程捕获，但它提供了`isCompletedAbnormally()`来检查任务是否已经抛出异常或已经被取消了，并通过`getException()`获取异常。

if (countTask.isCompletedAbnormally()){
                System.out.println(countTask.getException());
            }