forkjoin用法_java fork join

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 @Override
    public long sumRecord(int toId, int fromId) {
        QueryWrapper<Users> queryWrapper = new QueryWrapper<>();
        // 用in语句合并成一条SQL，避免多次请求数据库的IO
        queryWrapper.ge("id", fromId);
        queryWrapper.le("id", toId);
        queryWrapper.select("IFNULL(SUM(money),0) as money");
        List<Users> users = usersMapper.selectList(queryWrapper);
        if (!CollectionUtils.isEmpty(users)) {
            return users.get(0).getMoney();
        }
        return 0;
    }
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    @Test
    public void sumTask() {
        long startTime = System.currentTimeMillis();
        ForkJoinPool pool = new ForkJoinPool(Runtime.getRuntime().availableProcessors() * 2);
        // 模拟千万数据
        int min = 1;
        int max = 17000003;
        SumTask sumTask = new SumTask(min, max, userService);
        pool.invoke(sumTask);

        System.out.println("总数 " + sumTask.join() +
                " 执行时间 " + (System.currentTimeMillis() - startTime));

    }

    public static final Integer THRESHOLD = 1000000;

    public static class SumTask extends RecursiveTask<Long> {

        int fromId;
        int toId;
        private UserService userService;


        public SumTask(int fromId, int toId, UserService userService) {
            this.fromId = fromId;
            this.toId = toId;
            this.userService = userService;
        }

        @Override
        protected Long compute() {
            if (toId - fromId < THRESHOLD) {
                return sumRecord(toId, fromId);
            } else {
                int mid = (fromId + toId) / 2;
                SumTask left = new SumTask(fromId, mid, userService);
                SumTask right = new SumTask(mid + 1, toId, userService);
                invokeAll(left, right);
                return left.join() + right.join();
            }
        }

        public Long sumRecord(int toId, int fromId) {
            System.out.println(" 参数 " + fromId + " " + toId);
            return userService.sumRecord(toId, fromId);
        }


    }
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