Question

我有一个使用axis2的异步Web服务，我使用相同的CallBack Hanlder调用两次不同的时间，如下所示：

stub.startGetData("Foo",callbackhandler)
 stub.startGetData("bar",callbackhanlder)

 ServiceCallBackhandler callbackhandler =  new ServiceCallBackhandler() { .....};
 //ServiceCallBackhanlder and stub are generated from a WSDL file

 Synchronized(callbackhandler){ callbackhandler.wait()}
 //remaining code to be executed
      ............
      ...........

这种情况下的问题是，一旦呼叫在stub.startGetData("Foo",callbackhandler)之后返回，就会执行“剩余代码”。我希望回调等到它还完成处理stub.startGetData("boo",callbackhandler)语句然后执行剩余的代码。有没有办法在不使用两个不同的回调函数的情况下完成它，因为两个返回值的处理是相同的。感谢。

Answer 1

我想你想要这样的东西......

 import java.util.concurrent.CountDownLatch;
 ...

 // set the latch count to the nuber of callbacks to wait for
 CountDownLatch latch = new CountDownLatch(2);

 ServiceCallBackhandler callbackhandler =  new ServiceCallBackhandler() {
      public void handleResponse(Response response) {
           .... do real work ...
           latch.countDown();
      }
 };

 stub.startGetData("Foo",callbackhandler)
 stub.startGetData("bar",callbackhanlder)

 // wait for both callbacks to occur
 latch.await();

另请参阅java.util.concurrent.Semaphore，但我认为CountDownLatch是您所描述的内容。

Answer 2

一般来说，如果想要等到N个不同对象的特定条件成立，他们应该考虑使用并发工具中的CyclicBarrier（N）或CountDownLatch（N）。

主体的基本结构：

CountDownLatch my_latch = new CountDownLatch( 2 );

// These objects perform some asynchronous function when
// their start() method is called.
AsyncObject ao1 = new AsyncObject( my_latch, ... );
AsyncObject ao2 = new AsyncObject( my_latch, ... );

ao1.start();  // asynchronous, returns immediately
ao2.start();  // asynchronous, returns immediately

// my_latch.await() blocks until the latch has counted down to 0 from 2
my_latch.await();

从希望在其工作完成或满足条件时“发出信号”的方法中：

{
    // ... work ...
    // work is complete

    the_latch_passed_in_to_this_object.countDown();
 }

异步Web服务，回调问题

2 个答案: