【java】【マルチスレッド】パラレル無関係タスクの全体的な結果取得を待つ

【シナリオ1】java 8フロー実装

       
        List root = roleDao.selRootPermission(roleReq.getApplicationId());//           

List> completableFutureList = root.stream()
                .map(permission -> CompletableFuture.supplyAsync(() -> {
                    System.out.println("------cu------" + Thread.currentThread().getName() + "*****" + Thread.currentThread().getId());
                    try {
                        cycle(permission);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return permission;
                }))  //    
                .collect(Collectors.toList());

        return completableFutureList.stream().map(CompletableFuture::join).collect(Collectors.toList());

【方案二】

CountDownLatch          ，         ，           。countDown()        ，            ，await()          0  ，                 。         0             0

        List root = roleDao.selRootPermission(roleReq.getApplicationId());//           

        //     ，           
        CountDownLatch end = new CountDownLatch(root.size());

        List total = new ArrayList<>();

        for (PermissionTree permission : root) {
            CompletableFuture future = CompletableFuture.runAsync(() -> {
                try {
                    cycle(permission);//           
//                    System.out.println("int" + Thread.currentThread().getName());
                } catch (Exception e) {
                    e.printStackTrace();
                }
                total.add(permission);
                end.countDown();
            });

//            System.out.println("out2" + Thread.currentThread().getName());
        }
        end.await();
//        System.out.println("out3" + Thread.currentThread().getName());
        return total;

 
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