ADDITIONAL SYSTEM INFORMATION :
MacBook Pro (15-inch, 2017)
3.1 GHz Intel Core i7
16 GB 2133 MHz LPDDR3

$uname -a
Darwin XXXXX 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 21 20:07:39 PDT 2018; root:xnu-3789.73.14~1/RELEASE_X86_64 x86_64

$ java --version
java 10.0.2 2018-07-17
Java(TM) SE Runtime Environment 18.3 (build 10.0.2+13)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.2+13, mixed mode)

A DESCRIPTION OF THE PROBLEM :
Reentrant stack trace leads to deadlock in nested Stream.parallel operations using a concurrent hash map.

I am building a data storage library in which I would like to use Stream.parallel. The application which uses this library also uses Stream.parallel and concurrent data structures to manipulate data. The combination leads to a deadlock with some very strange stack traces where the compute method called in the outer loop appears to be reentrant.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached source code in either of two parallel execution modes which fail. (line 24 & 25)
Three additional modes of execution succeed. (lines 28, 29 & 30)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A thread's stack trace should never contain line 87 more than once. The code should not deadlock
ACTUAL -
Found one Java-level deadlock:
=============================
"outer pool1":
  waiting to lock monitor 0x00007ff6ca8aba00 (object 0x00000006cfb8a370, a java.util.concurrent.ConcurrentHashMap$ReservationNode),
  which is held by "outer pool2"
"outer pool2":
  waiting to lock monitor 0x00007ff6ca085800 (object 0x00000006cfb30b58, a java.util.concurrent.ConcurrentHashMap$ReservationNode),
  which is held by "outer pool1"

Java stack information for the threads listed above:
===================================================
"outer pool1":
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1938)
- waiting to lock <0x00000006cfb8a370> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1961)
- locked <0x00000006cf9a8c60> (a java.util.concurrent.ConcurrentHashMap$Node)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1961)
- locked <0x00000006cf81c3b0> (a java.util.concurrent.ConcurrentHashMap$Node)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1961)
- locked <0x00000006cf81c1c0> (a java.util.concurrent.ConcurrentHashMap$Node)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1922)
- locked <0x00000006cfb31d80> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1961)
- locked <0x00000006cfa26d78> (a java.util.concurrent.ConcurrentHashMap$Node)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1922)
- locked <0x00000006cfb30b58> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1922)
- locked <0x00000006cfb195f0> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinTask.doInvoke(java.base@10.0.2/ForkJoinTask.java:408)
at java.util.concurrent.ForkJoinTask.invoke(java.base@10.0.2/ForkJoinTask.java:736)
at java.util.stream.ForEachOps$ForEachOp.evaluateParallel(java.base@10.0.2/ForEachOps.java:159)
at java.util.stream.ForEachOps$ForEachOp$OfLong.evaluateParallel(java.base@10.0.2/ForEachOps.java:209)
at java.util.stream.AbstractPipeline.evaluate(java.base@10.0.2/AbstractPipeline.java:233)
at java.util.stream.LongPipeline.forEach(java.base@10.0.2/LongPipeline.java:421)
at java.util.stream.LongPipeline$Head.forEach(java.base@10.0.2/LongPipeline.java:579)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$5(NestedParallel.java:84)
at com.upserve.NestedParallel$$Lambda$5/2101440631.run(Unknown Source)
at java.util.concurrent.ForkJoinTask$AdaptedRunnableAction.exec(java.base@10.0.2/ForkJoinTask.java:1407)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.runWorker(java.base@10.0.2/ForkJoinPool.java:1603)
at java.util.concurrent.ForkJoinWorkerThread.run(java.base@10.0.2/ForkJoinWorkerThread.java:177)
"outer pool2":
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1938)
- waiting to lock <0x00000006cfb30b58> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.awaitJoin(java.base@10.0.2/ForkJoinPool.java:1713)
at java.util.concurrent.ForkJoinTask.doJoin(java.base@10.0.2/ForkJoinTask.java:397)
at java.util.concurrent.ForkJoinTask.get(java.base@10.0.2/ForkJoinTask.java:1004)
at com.upserve.NestedParallel.streamParallelInnerTask(NestedParallel.java:172)
at com.upserve.NestedParallel.lambda$biFunction$9(NestedParallel.java:147)
at com.upserve.NestedParallel$$Lambda$12/1333040169.apply(Unknown Source)
at java.util.concurrent.ConcurrentHashMap.compute(java.base@10.0.2/ConcurrentHashMap.java:1922)
- locked <0x00000006cfb8a370> (a java.util.concurrent.ConcurrentHashMap$ReservationNode)
at com.upserve.NestedParallel.lambda$streamParallelOuterTask$4(NestedParallel.java:87)
at com.upserve.NestedParallel$$Lambda$6/354291670.accept(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfLong.accept(java.base@10.0.2/ForEachOps.java:225)
at java.util.Random$RandomLongsSpliterator.forEachRemaining(java.base@10.0.2/Random.java:1099)
at java.util.Spliterator$OfLong.forEachRemaining(java.base@10.0.2/Spliterator.java:763)
at java.util.stream.AbstractPipeline.copyInto(java.base@10.0.2/AbstractPipeline.java:484)
at java.util.stream.ForEachOps$ForEachTask.compute(java.base@10.0.2/ForEachOps.java:290)
at java.util.concurrent.CountedCompleter.exec(java.base@10.0.2/CountedCompleter.java:746)
at java.util.concurrent.ForkJoinTask.doExec(java.base@10.0.2/ForkJoinTask.java:290)
at java.util.concurrent.ForkJoinPool.runWorker(java.base@10.0.2/ForkJoinPool.java:1603)
at java.util.concurrent.ForkJoinWorkerThread.run(java.base@10.0.2/ForkJoinWorkerThread.java:177)

Found 1 deadlock.


---------- BEGIN SOURCE ----------
package com.upserve;

import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.function.*;
import java.util.stream.*;

public class NestedParallel implements Runnable {

    static final String STREAM_PARALLEL = "STREAM PARALLEL";
    static final String LOOP_PARALLEL = "LOOP PARALLEL";
    static final String SERIAL = "SERIAL";

    final ConcurrentMap<String, Long> concurrentMap;
    final ExecutorService outerPool;
    final ExecutorService innerPool;
    final Random random;
    final String innerLoop;
    final String outerLoop;

    public static void main(String[] args){
// // DEADLOCKS
        NestedParallel nestedParallel = new NestedParallel(STREAM_PARALLEL, STREAM_PARALLEL);
// NestedParallel nestedParallel = new NestedParallel(STREAM_PARALLEL, LOOP_PARALLEL);

// // SUCCESSS
// NestedParallel nestedParallel = new NestedParallel(STREAM_PARALLEL, SERIAL);
// NestedParallel nestedParallel = new NestedParallel(LOOP_PARALLEL, STREAM_PARALLEL);
// NestedParallel nestedParallel = new NestedParallel(SERIAL, LOOP_PARALLEL); // SLOW!

        System.out.println("starting");
        nestedParallel.run();
        System.out.println("finished");
    }

    public NestedParallel(String outerLoop, String innerLoop) {

        concurrentMap = new ConcurrentHashMap<>();

        this.innerLoop = innerLoop;
        this.outerLoop = outerLoop;

        Function<String, ForkJoinPool.ForkJoinWorkerThreadFactory> threadFactoryFunction = name -> pool ->
        {
            final ForkJoinWorkerThread worker = ForkJoinPool.defaultForkJoinWorkerThreadFactory.newThread(pool);
            worker.setName(name + worker.getPoolIndex());
            return worker;
        };

        Function<String, ForkJoinPool> forkJoinPoolFunction = name -> new ForkJoinPool(
                Runtime.getRuntime().availableProcessors(),
                threadFactoryFunction.apply(name),
                (t, e) -> {
                    System.out.println("In pool " + name + ", thread " + t + " threw exception: " + e);
                },
                true
        );

        outerPool = forkJoinPoolFunction.apply("outer pool");
        innerPool = forkJoinPoolFunction.apply("inner pool");

        random = new Random();
    }

    @Override
    public void run() {
        if (STREAM_PARALLEL.equals(outerLoop)) {
            streamParallelOuterTask();
        } else if (LOOP_PARALLEL.equals(outerLoop)) {
            loopParallelOuterTask();
        } else if (SERIAL.equals(outerLoop)) {
            serialOuterTask();
        } else {
            throw new RuntimeException("Invalid command: " + outerLoop);
        }
    }

    private void streamParallelOuterTask(){
        Future future = outerPool.submit(() -> {
            random
                    .longs(1_000_000, 0, 1_000)
                    .parallel()
                    .forEach(val -> {
                                if (val % 1017 == 0) System.out.println("Outer Task Thread:" + Thread.currentThread().getName());
                                String key = String.valueOf(val);
                                concurrentMap.compute(key, biFunction(val));
                            }
                    );
        });

        try {
            future.get();
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted " + Thread.currentThread().getName(), e);
        } catch (ExecutionException e) {
            throw new RuntimeException("Failed " + Thread.currentThread().getName(), e);
        }
    }

    private void loopParallelOuterTask(){
        List<Long> vals = random.longs(1_000_000, 0, 1_000).boxed().collect(Collectors.toList());

        List<Future> futures = new ArrayList<>();
        for(Long val: vals) {
            futures.add(outerPool.submit(() -> {
                if (val % 1000 == 0) System.out.println("Outer Task Thread:" + Thread.currentThread().getName());
                String key = String.valueOf(val);
                concurrentMap.compute(key, biFunction(val));
            }));
        }

        futures.forEach(f -> {
            try {
                f.get();
            } catch (InterruptedException e) {
                throw new RuntimeException("Interrupted " + Thread.currentThread().getName(), e);
            } catch (ExecutionException e) {
                throw new RuntimeException("Failed " + Thread.currentThread().getName(), e);
            }
        });
    }

    private void serialOuterTask() {
        random
                .longs(1_000_000, 0, 1_000)
                .forEach(val -> {
                            if (val % 1000 == 0) System.out.println("Outer Task Thread:" + Thread.currentThread().getName());
                            String key = String.valueOf(val);
                            concurrentMap.compute(key, biFunction(val));
                        }
                );
    }

    private BiFunction<String, Long, Long> biFunction(long val) {
        return (k, v) -> {
            if (v == null) {
                v = val;
            } else {
                v += val;
            }

            final Long vMod = v % 10_000;

            // Do some naive task
            if (STREAM_PARALLEL.equals(innerLoop)) {
                return streamParallelInnerTask(vMod);

            } else if (LOOP_PARALLEL.equals(innerLoop)) {
                return loopParallelInnerTask(vMod);

            } else if (SERIAL.equals(innerLoop)) {
                return serialInnerTask(vMod);
            } else {
                throw new RuntimeException("Invalid command: " + innerLoop);
            }
        };
    }

    private Long streamParallelInnerTask(long vMod) {
        LongAdder longAdder = new LongAdder();
        // If outerPool is used again, no deadlock but process will livelock after a while
        Future future = innerPool.submit(() -> {
            LongStream.range(1, vMod)
                    .parallel()
                    .forEach(value -> {
                        // System.out.println("Inner Task Thread: " +Thread.currentThread().getName());
                        longAdder.add(value);
                    });
        });
        try {
            future.get();
        } catch (InterruptedException e) {
            throw new RuntimeException("Interrupted " + Thread.currentThread().getName(), e);
        } catch (ExecutionException e) {
            throw new RuntimeException("Failed " + Thread.currentThread().getName(), e);
        }
        return longAdder.longValue();
    }

    private Long loopParallelInnerTask(long vMod) {
        LongAdder longAdder = new LongAdder();
        List<Future> futures = new ArrayList<>();
        for (long i=0; i<vMod; i++) {
            final Long innerVal = i;
            // Can not use outerPool again here as it causes livelock with all thread waiting
            futures.add(innerPool.submit(() -> {
// System.out.println("Inner Task Thread: " +Thread.currentThread().getName());
                longAdder.add(innerVal);
            }));
        }

        futures.forEach(f -> {
            try {
                f.get();
            } catch (InterruptedException e) {
                throw new RuntimeException("Interrupted " + Thread.currentThread().getName(), e);
            } catch (ExecutionException e) {
                throw new RuntimeException("Failed " + Thread.currentThread().getName(), e);
            }
        });
        return longAdder.longValue();
    }

    private Long serialInnerTask(long vMod) {
        LongAdder longAdder = new LongAdder();
        LongStream.range(1, vMod)
                .forEach(value -> {
                    // System.out.println("Inner Task Thread: " +Thread.currentThread().getName());
                    longAdder.add(value);
                });
        return longAdder.longValue();
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Beware of Stream.parallel and where it may be used as an internal concern in a library.
Use other methods to parallelize high levels of an application that use Stream.parallel internally.

FREQUENCY : always