ForkJoinPool性能Java 8 vs 11

package com.sarvagya;

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.stream.Collectors;

public class Streamer {
    private static final int LOOP_COUNT  = 2000;
    public static void main(String[] args){
        try{
            for(int i = 0; i < LOOP_COUNT; ++i){
                poolRunner();
                System.out.println("done loop " + i);
                try{
                    Thread.sleep(50L);
                }
                catch (Exception e){
                    System.out.println(e);
                }
            }
        }
        catch (ExecutionException | InterruptedException e){
            System.out.println(e);
        }

        // Add a delay outside the loop to make sure all daemon threads are cleared before main exits.
        try{
            Thread.sleep(10 * 60 * 1000L);
        }
        catch (Exception e){
            System.out.println(e);
        }
    }

    /**
     * poolRunner method.
     * Assume I don't have any control over this method e.g. done by some library.
     * @throws InterruptedException
     * @throws ExecutionException
     */
    private static void poolRunner() throws InterruptedException, ExecutionException {
        ForkJoinPool pool = new ForkJoinPool();
        pool.submit(() ->{
            List<Integer> numbers = Arrays.asList(1,2,3,4,5,6,7,8,9,10, 11,12,14,15,16);
            List<Integer> collect = numbers.stream()
                    .parallel()
                    .filter(xx -> xx > 5)
                    .collect(Collectors.toList());
            System.out.println(collect);
        }).get();
    }
}

在上面的代码中,poolRunner方法正在创建一个ForkJoinPool并向其提交一些任务.当使用Java 8并将LOOP_COUNT保持为2000时,我们可以看到创建的最大线程大约为3600,如下所示

图：分析

图：线程信息.

经过一段时间后,所有这些线程都会下降到接近10.但是,在OpenJDK 11中保持相同的LOOP_COUNT会产生以下错误：

[28.822s][warning][os,thread] Failed to start thread - pthread_create failed (EAGAIN) for attributes: stacksize: 1024k, guardsize: 4k, detached.
[28.822s][warning][os,thread] Failed to start thread - pthread_create failed (EAGAIN) for attributes: stacksize: 1024k, guardsize: 4k, detached.
[28.822s][warning][os,thread] Failed to start thread - pthread_create failed (EAGAIN) for attributes: stacksize: 1024k, guardsize: 4k, detached.
Exception in thread "ForkJoinPool-509-worker-5" java.lang.OutOfMemoryError: unable to create native thread: possibly out of memory or process/resource limits reached
    at java.base/java.lang.Thread.start0(Native Method)
    at java.base/java.lang.Thread.start(Thread.java:803)
    at java.base/java.util.concurrent.ForkJoinPool.createWorker(ForkJoinPool.java:1329)
    at java.base/java.util.concurrent.ForkJoinPool.tryAddWorker(ForkJoinPool.java:1352)
    at java.base/java.util.concurrent.ForkJoinPool.signalWork(ForkJoinPool.java:1476)
    at java.base/java.util.concurrent.ForkJoinPool.deregisterWorker(ForkJoinPool.java:1458)
    at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:187)

它很快达到最大线程限制.将LOOP_COUNT保持为500,工作正常,但是,这些线程非常缓慢地清除并达到大约500个线程的平台.见下图：

图：OpenJDK 11中的线程信息

图：OpenJDK中的分析11

线程在JDK 8中是PARKED,但在JDK 11中是WAIT.在Java 11中也应该减少守护程序线程的数量,但是它很慢并且不能按预期工作.而且,假设我无法控制poolRunner方法.考虑这种方法是由一些外部库提供的.

这是OpenJDK 11的问题,还是我在代码中做错了什么.谢谢.

In above code, I am creating a ForkJoinPool and submitting some tasks to it.

实际上,你正在创建2000个ForkJoinPool实例……

您应该创建一个具有适合当前任务的并行度(即线程数)的ForkJoinPool,而不是这样做.

创建大量(即数千个)线程是一个非常糟糕的主意.即使您可以在不触发OOME的情况下执行此操作,您将消耗大量的堆栈和堆内存,并在调度程序和垃圾收集器上施加大量负载……没有任何实际好处.