CompletableFuture-汇总未来的快速失败

问题描述

我一直在使用 CompletableFuture.allOf（...）助手来创建汇总期货，这些期货只有在其复合期货被标记为完成时才会完成，即：

I have been using the CompletableFuture.allOf(...) helper to create aggregate futures that will only become "done" when their composite futures are marked as complete, i.e:

CompletableFuture<?> future1 = new CompletableFuture<>();
CompletableFuture<?> future2 = new CompletableFuture<>();
CompletableFuture<?> future3 = new CompletableFuture<>();

CompletableFuture<?> future = CompletableFuture.allOf(future1, future2, future3);

我想对此功能稍作改动，在以下情况下，总的未来市场是完整的：

I would like a slight variation on this functionality, where the aggregate future is market as complete when:

• 所有期货均已成功完成 OR


• 任何一项期货均已完成不成功

在后一种情况下，总期货应立即（例外）完成，而不必等待其他期货完成，例如 fail-fast 。

In the latter case, the aggregate future should complete (exceptionally) immediately, and not have to wait for the other futures to complete, i.e. to fail-fast.

为了说明这一点，与 CompletableFuture.allOf（...）考虑一下：

To illustrate this in contrast to CompletableFuture.allOf(...) consider this:

// First future completed, gotta wait for the rest of them...
future1.complete(null);
System.out.println("Future1 Complete, aggregate status: " + future.isDone());

// Second feature was erroneous! I'd like the aggregate to now be completed with failure
future2.completeExceptionally(new Exception());
System.out.println("Future2 Complete, aggregate status: " + future.isDone());

// Finally complete the third future, that will mark the aggregate as done
future3.complete(null);
System.out.println("Future3 Complete, aggregate status: " + future.isDone());

使用 allOf（...），此代码产生：

Future1 Complete, aggregate status: false
Future2 Complete, aggregate status: false
Future3 Complete, aggregate status: true

而Feature2完成后，我的替代汇总实现将返回 true

Whereas my alternative aggregate implementation would return "true" after Feature2 was completed, given it was an exceptional.

我在Java标准库中找不到能够帮助我实现这一目标的工具，

I cannot find any utils in the Java standard library that will help me achieve this, which feels strange... given it's a relatively vanilla use-case.

看着 CompletableFuture.allOf（...）这些场景背后的逻辑非常复杂。我不愿意自己写这个，我想知道是否还有其他选择？

Looking at the implementation of CompletableFuture.allOf(...) it's fairly obvious that the logic behind these scenarios is fairly complex. I'd loathe to have to write this myself, I was wondering if there are any alternatives?

推荐答案

尽管在语法上不那么甜美作为 CompletableFuture.allOf（...）方法，看来 thenCompose（...）可以提供解决方案：

Although not as syntactically sweet as the CompletableFuture.allOf(...) method, it appears that thenCompose(...) may offer the solution:

CompletableFuture<?> future = future1.thenCompose((f) -> future2).thenCompose((f) -> future3);

这将产生所需的内容：

Future1 Complete, aggregate status: false
Future2 Complete, aggregate status: true
Future3 Complete, aggregate status: true

可以将其包装在帮助程序方法中，该方法可以为调用方提供一些语法上的技巧：

This could be wrapped up in a helper method which would offer some syntactic niceties to the caller:

private static CompletableFuture<?> composed(CompletableFuture<?> ... futures) {

    // Complete when ALL the underlying futures are completed
    CompletableFuture<?> allComplete = CompletableFuture.allOf(futures);

    // Complete when ANY of the underlying futures are exceptional
    CompletableFuture<?> anyException = new CompletableFuture<>();
    for (CompletableFuture<?> completableFuture : futures) {
        completableFuture.exceptionally((t) -> {
            anyException.completeExceptionally(t);
            return null;
        });
    }

    // Complete when either of the above are satisfied
    return CompletableFuture.anyOf(allComplete, anyException);
}

允许：

CompletableFuture<?> future = composed(future1, future2, future3);

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