java 异步方法的同步版本
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Sync version of async method
提问by hpique
What's the best way to make a synchronous version of an asynchronous method in Java?
在 Java 中制作异步方法的同步版本的最佳方法是什么？
Say you have a class with these two methods:
假设您有一个包含这两种方法的类：
asyncDoSomething(); // Starts an asynchronous task
onFinishDoSomething(); // Called when the task is finished
How would you implement a synchronous doSomething()that does not return until the task is finished?
你将如何实现一个doSomething()直到任务完成才返回的同步？
回答by rodion
Have a look at CountDownLatch. You can emulate the desired synchronous behaviour with something like this:
看看CountDownLatch。您可以使用以下内容模拟所需的同步行为：
private CountDownLatch doneSignal = new CountDownLatch(1);
void main() throws InterruptedException{
asyncDoSomething();
//wait until doneSignal.countDown() is called
doneSignal.await();
}
void onFinishDoSomething(){
//do something ...
//then signal the end of work
doneSignal.countDown();
}
You can also achieve the same behaviour using CyclicBarrierwith 2 parties like this:
您还可以CyclicBarrier像这样使用2 方来实现相同的行为：
private CyclicBarrier barrier = new CyclicBarrier(2);
void main() throws InterruptedException{
asyncDoSomething();
//wait until other party calls barrier.await()
barrier.await();
}
void onFinishDoSomething() throws InterruptedException{
//do something ...
//then signal the end of work
barrier.await();
}
If you have control over the source-code of asyncDoSomething()I would, however, recommend redesigning it to return a Future<Void>object instead. By doing this you could easily switch between asynchronous/synchronous behaviour when needed like this:
但是，如果您可以控制asyncDoSomething()I的源代码，则建议重新设计它以返回一个Future<Void>对象。通过这样做，您可以在需要时轻松地在异步/同步行为之间切换，如下所示：
void asynchronousMain(){
asyncDoSomethig(); //ignore the return result
}
void synchronousMain() throws Exception{
Future<Void> f = asyncDoSomething();
//wait synchronously for result
f.get();
}
