Java 可等待对象容器

Question

现有框架是否实现了以下方法？

public class WaitableContainer<T> {
  private T object;
  public <T> peekAwait() {...} // returns object if object !=null or makes the caller thread sleep until object != null
  public actuate(T object) {
    this.object = object; // here all sleeping threads must awake and receive the new object
  }
}

需要某种对象包装器，它将使调用者线程一直运行，直到另一个线程设置该对象。

Answer 1

这听起来像 CompletableFuture 。

// container.actuate(o); becomes
future.complete(o);

// container.peekAwait(); becomes
future.get();

如果您无法使用 Java 8，FutureTask是一个不错的解决方法选择，但您不需要显式设置它，而是提供一个返回您想要设置的值的 Callable。

final FutureTask<Object> lazyLoadedData = new FutureTask<>(() -> expensiveIO());

...

if (!lazyLoadedData.isDone()) {
    synchronized(lazyLoadedData) {
        if (!lazyLoadedData.isDone()) {
            // run() does the computation and sets the data
            // essentially, lazyLoadedData.set(expensiveIO())
            lazyLoadedData.run();
        }
    }
}
// Data is available
lazyLoadedData.get();

如果您计划让 ExecutorService 执行此操作，它已经返回一个 Future；

final FutureTask<Object> future = executorService.submit(() -> expensiveIO());

// Now you just need to call get()
future.get();