java - 使异步查询同步

Question

我有一个底层异步乱序查询/响应系统，我想使其同步。可以通过使用唯一 ID 标记查询来映射查询和响应，这些 ID 将伴随相应的响应。

我试图让它同步使用两个 ConcurrentHashMap s:一个从 ID 映射到结果，一个从相同的 ID 映射到 CountDownLatch es。执行查询时，代码如下所示:

public Result execute(Query query) throws InterruptedException {
    int id = atomicInteger.incrementAndGet();
    CountDownLatch latch = new CountDownLatch(1);
    latchMap.put(id, latch);
    query.executeAsyncWithId(id); // Probably returns before result is ready
    try {
        latch.await(); // Blocks until result is ready
        return resultMap.remove(id);
    } catch (InterruptedException e) {
        latchMap.remove(id); // We are not waiting anymore
        throw e;
    }
}

以及处理传入结果的代码:

public void handleResult(Result result) {
    int id = result.getId();
    CountDownLatch latch = latchMap.remove(id);
    if (latch == null) {
        return; // Nobody wants result
    }
    resultMap.put(id, result);
    latch.countDown();
}

此方法从一个线程调用，该线程从底层系统读取所有传入结果(只有一个这样的读取器线程)。

首先，我不确定线程​​安全性，但似乎也没有必要为此使用两个 HashMap(特别是因为 ID 永远不会被重用)。有什么改进的想法吗？

Answer 1

受this answer to a similar question启发的新尝试:

public class ResultFuture {

    private volatile Result result = null;
    private final CountDownLatch latch = new CountDownLatch(1);

    public Result get() throws InterruptedException {
        latch.await();
        return result;
    }

    public void set(Result result) {
        this.result = result;
        latch.countDown();
    }
}

现在我只需要这些 ResultFuture 中的一个 HashMap:

public Result execute(Query query) throws InterruptedException {
    int id = atomicInteger.incrementAndGet();
    ResultFuture resultFuture = new ResultFuture();
    resultFutureMap.put(id, resultFuture);
    query.executeAsyncWithId(id); // Probably returns before result is ready
    try {
        return resultFuture.get(); // Blocks until result is ready
    } finally {
        resultFutureMap.remove(id);
    }
}

public void handleResult(Result result) {
    int id = result.getId();
    ResultFuture resultFuture = resultFutureMap.get(id);
    if (resultFuture == null) {
        return; // Nobody wants result
    }
    resultFuture.set(result);
}