JavaEE应用服务器中的CompletableFuture/parallelStream

Question

鉴于新的Java8,我们为异步任务获得了非常好的功能,例如CompletableFuture和.paralellStream().如果你在Java SE中运行它,因为我已经理解它你将使用ForkJoinPool,但是如果我在例如Wildfly或TomcatEE中运行以下示例会发生什么？

//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())

会发生什么,我将从哪里借用我的资源

1. 这些示例在@Stateful bean中运行
2. 这些示例在@Stateless bean中运行
3. 这些示例在CDI bean中运行

Answer 1

您不应该在Java EE中使用ForkJoinPool.只有app服务器应该提供并行性的构造(如Java EE 7中的ManagedExecutorService),因为线程必须由容器管理.

奇怪的是,在这个答案中提到的邮件列表中有一条消息声称ForkJoinPool会优雅地降级为EE容器中的单线程.我用glassfish 4.1测试了这个,并创建了常用的线程.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

当大多数单独的规范将利用SE 8功能时,Java EE 8上可能会出现降级.

编辑

我检查了glassfish 4.1.1源代码,并没有单独使用ForkJoinPool,ForkJoinWorkerThreadFactory或ForkJoinWorkerThread.因此,应用服务器管理的并行性资源不是基于任何这些结构.不幸的是,实际上没有可用的降级机制.