I have some problems while using ThreadPoolExecutor and I cannot figure it out.
I try to use two List<CompletableFuture<Void>> taskList lists to store tasks and then submit to a threadpool but all threads are blocked and can not handle new requests. The code like this:

There is a threadpool.

public class AsyncInvoker  {

    public class AsyncInvoker  {

    private ExecutorService excutePool;


    public AsyncInvoker(int thread, int queue) {

        excutePool= new ThreadPoolExecutor(thread, thread,
            0, TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<>(queue), new ThreadPoolExecutor.AbortPolicy());
    }


   public InvokeCollection newCollection() {
       return new InvokeCollection();
   }

    public class InvokeCollection {

        private List<CompletableFuture<Void>> taskList = new ArrayList<>();

        public void add(Runnable task) {
            CompletableFuture<Void> future = CompletableFuture.runAsync(task, excutePool);
            taskList.add(future);
        }

        public void invokeAll() {
            try {
                CompletableFuture<Void> future = CompletableFuture.allOf(taskList.toArray(new CompletableFuture[0]));
            future.get();
            } catch (Exception e) {
            e.printStackTrace();
            }
        }
    }
}

And I submit jobs like this:

@RestController
public class TestController {
    AsyncInvoker asyncInvoker = new AsyncInvoker(10,1000000);
    @GetMapping("test")
    public void test(){
        System.out.println("request=======================");
        AsyncInvoker.InvokeCollection outer = asyncInvoker.newCollection();
        for (int i = 0; i < 10; i++) {
           outer.add(()->{
               AsyncInvoker.InvokeCollection inner = asyncInvoker.newCollection();
               for (int j = 0; j < 100; j++) {
                   inner.add(()->{
                       try {
                           Thread.sleep(100);
                           System.out.println("===");
                       }catch (Exception e) {
                           e.printStackTrace();
                       }
                   });
               }
               inner.invokeAll();
           });
            System.out.println("i " + i);
        }
        outer.invokeAll();
    }
}

When I request the TestController multiple times, there is several === print in idea’s console, and as I request repeatly, there is no more === prints. I think the thread is blocked. The thread dump like this:

   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x000000076c9923a0> (a java.util.concurrent.CompletableFuture$Signaller)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
        at java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1707)
        at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3334)
        at java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1742)
        at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1908)
        at com.aa.AsyncInvoker$InvokeCollection.invokeAll(AsyncInvoker.java:59)

And then, if there is just one AsyncInvoker.InvokeCollection instead of outer and inner,and I add all tasks into one collection, it works well.

and also, if I use private ForkJoinPool forkJoinPool = new ForkJoinPool(thread,new SafeForkJoinWorkerThreadFactory(), null, false); to handle tasks, it also looks good.

So I don’t know why the code write above doesn’t work, is the thread blocked,why? and why ForkJoinPool is better than ThreadPoolExecutor in this case.

Can someone give me some help? Thanks a lot!!