Java 中 BlockingQueue 的异步等价物？

Question

我正在寻找一个与java.util.concurrent.BlockingQueue等效的异步（非阻塞）队列。 它的界面将包括：

public interface AsynchronousBlockingQueue<E> {
    // - if the queue is empty, return a new CompletableFuture,
    //   that will be completed next time `add` is called
    // - if the queue is not empty, return a completed CompletableFuture,
         containing the first element of the list
    public CompletableFuture<E> poll();

    // if polling is in progress, complete the ongoing polling CompletableFuture.
    // otherwise, add the element to the queue
    public synchronized void add(E element);
}

如果这很重要，应该只有一个轮询线程，并且轮询应该按顺序进行（ poll已经在进行时不会调用 poll）。

我预计它已经存在于 JVM 中，但我找不到它，当然我宁愿使用 JVM 中的东西也不愿自己编写。

另一个限制是，我坚持使用 Java 8（尽管我绝对有兴趣了解最新版本中存在的内容）。

Answer 1

所以最后我写了我自己的 class ......有兴趣评论:)

import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.CompletableFuture;

public class AsynchronousBlockingQueue<E> {
    CompletableFuture<E> incompletePolling = null;
    Queue<E> elementsQueue = new LinkedList<>();

    // if the queue is empty, return a new CompletableFuture, that will be completed next time `add` is called
    // if the queue is not empty, return a completed CompletableFuture containing the first element of the list
    public synchronized CompletableFuture<E> poll() {
        // polling must be done sequentially, so this shouldn't be called if there is a poll ongoing.
        if (incompletePolling != null)
            throw new IllegalStateException("Polling is already ongoing");
        if (elementsQueue.isEmpty()) {
            incompletePolling = new CompletableFuture<>();
            return incompletePolling;
        }
        CompletableFuture<E> result = new CompletableFuture<>();
        result.complete(elementsQueue.poll());
        return result;
    }

    // if polling is in progress, complete the ongoing polling CompletableFuture.
    // otherwise, add the element to the queue
    public synchronized void add(E element) {
        if (incompletePolling != null) {
            CompletableFuture<E> result = incompletePolling;
            // removing must be done first because the completion could trigger code that needs the queue state to be valid
            incompletePolling = null;
            result.complete(element);
            return;
        }
        elementsQueue.add(element);
    }


}