从线程中返回值的相关问题

Question

程序的方法中有一个 HandlerThread。在线程中改变了一个值，然后我想把它返回到 test()方法。有什么方法能实现呢？

public void test()
{   
    Thread uiThread = new HandlerThread("UIHandler"){
        public synchronized void run(){
            int value; 
            value = 2; //To be returned to test()
        }
    };
    uiThread.start();
}

Answer 1

你可以使用一个本地的 final 变量，变量需要是 non-primitive 类型，所以你可以使用一个数组。也需要同步两个线程，例如使用一个 CountDownLatch:

public void test()
{   
    final CountDownLatch latch = new CountDownLatch(1);
    final int[] value = new int[1];
    Thread uiThread = new HandlerThread("UIHandler"){
        @Override
        public synchronized void run(){
            value[0] = 2;
            latch.countDown(); // Release await() in the test thread.
        }
    };
    uiThread.start();
    latch.await(); // Wait for countDown() in the UI thread.
    // value[0] holds 2 at this point.
}

也可以使用 Executor 和 Callable：

public void test() throws InterruptedException, ExecutionException
{   
    ExecutorService executor = Executors.newSingleThreadExecutor();
    Callable<Integer> callable = new Callable<Integer>() {
        @Override
        public Integer call() {
            return 2;
        }
    };
    Future<Integer> future = executor.submit(callable);
    // future.get() returns 2
    executor.shutdown();
}