CyclicBarrier cb = new CyclicBarrier(4, new MainTask()); ExecutorService pool = Executors.newCachedThreadPool(); pool.execute(new ChildTask(cb)); pool.execute(new ChildTask(cb)); pool.execute(new ChildTask(cb)); pool.execute(new ChildTask(cb));可以用CyclicBarrier,等到4個子線程執行完畢后會調用MainTask（）線程。這樣相當于獲取了4個子線程已經死亡信息