CompletableFuture/parallelStream 在 JavaEE 应用程序服务器中

Question

鉴于新的 Java8 我们正在为异步任务提供非常好的功能，例如CompletableFuture 和 .paralellStream()。如果你在 Java SE 中运行这个，正如我所理解的那样，你将使用 ForkJoinPool，但是如果我运行下面的例子会发生什么Wildfly 还是 TomcatEE？

//Here I start a comp.Future without giving an Executor
test = CompletableFuture.supplyAsync(() -> timeConsumingMethod());
//Here I start a parallel stream 
mList.paralell().filter(...).collect(Collectors.toList())

如果

会发生什么，我将从哪里借用我的资源

@Stateful bean
示例是运行 @Stateless bean
CDI bean

Answer 1

你不应该在 Java EE 中使用 ForkJoinPool。只有应用服务器应该提供并行结构（如 ManagedExecutorService in Java EE 7), because threads have to be managed by the container.

奇怪的是，this answer 中提到的邮件列表中有一条消息声称 ForkJoinPool 将在 EE 容器中优雅地降级为单线程。我已经用 glassfish 4.1 对此进行了测试，并且创建了通常的线程。运行此代码：

@Singleton
public class SomeSingleton {
    public void fireStream() {
        IntStream.range(0, 32)
            .parallel()
            .mapToObj(i -> String.format("Task %d on thread %s", 
                i, Thread.currentThread().getName()))
            .forEach(System.out::println);
    }
}

我得到以下输出：

Info:   Task 20 on thread http-listener-1(4)
Info:   Task 10 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 21 on thread http-listener-1(4)
Info:   Task 11 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 22 on thread http-listener-1(4)
Info:   Task 8 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 23 on thread http-listener-1(4)
Info:   Task 9 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 18 on thread http-listener-1(4)
Info:   Task 14 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 19 on thread http-listener-1(4)
Info:   Task 15 on thread ForkJoinPool.commonPool-worker-3
Info:   Task 16 on thread http-listener-1(4)
Info:   Task 17 on thread http-listener-1(4)
Info:   Task 4 on thread http-listener-1(4)
Info:   Task 5 on thread http-listener-1(4)
Info:   Task 6 on thread http-listener-1(4)
Info:   Task 7 on thread http-listener-1(4)
Info:   Task 2 on thread http-listener-1(4)
Info:   Task 3 on thread http-listener-1(4)
Info:   Task 0 on thread http-listener-1(4)
Info:   Task 1 on thread http-listener-1(4)
Info:   Task 26 on thread http-listener-1(4)
Info:   Task 27 on thread http-listener-1(4)
Info:   Task 24 on thread http-listener-1(4)
Info:   Task 25 on thread http-listener-1(4)
Info:   Task 12 on thread http-listener-1(4)
Info:   Task 13 on thread http-listener-1(4)
Info:   Task 30 on thread http-listener-1(4)
Info:   Task 31 on thread http-listener-1(4)
Info:   Task 28 on thread ForkJoinPool.commonPool-worker-0
Info:   Task 29 on thread ForkJoinPool.commonPool-worker-0

也许降级将在 Java EE 8 上可用，届时大多数单独的规范将利用 SE 8 功能。

编辑

我查看了 glassfish 4.1.1 源代码，没有单独使用 ForkJoinPool、ForkJoinWorkerThreadFactory 或 ForkJoinWorkerThread。因此，应用服务器管理的并行资源不基于任何这些结构。不幸的是，确实没有可用的降级机制。

CompletableFuture/parallelStream 在 JavaEE 应用程序服务器中

CompletableFuture/parallelStream in JavaEE app server

java

jakarta-ee

asynchronous

java-ee-7

completable-future