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，但是如果我在例如运行以下示例中会发生什么？ 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

，我会从哪里借用资源

示例在@Stateful bean
示例在@Stateless bean
示例在CDI bean中运行

Answer 1

您不应在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会优雅地降级为EE容器中的单线程。我用glassfish 4.1对此进行了测试，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

当大多数个别规范将利用SE 8功能时，Java EE 8上可能会出现降级。

修改

我已检查了glassfish 4.1.1源代码，并且没有ForkJoinPool，ForkJoinWorkerThreadFactory或ForkJoinWorkerThread的使用。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，确实没有可用的退化机制。

JavaEE应用服务器中的CompletableFuture / parallelStream

1 个答案: