Lots for threads are waiting for ForkJoinPool

Question

My java application stopped working . While looking into stack dump I found out that there are 28 threads which are waiting for a particular thread . I am using newSingleThreadScheduledExecutor at the start of application and stop it during shutdown of application.

I am not sure how to proceed from here . Is it the root cause of issue or am I missing something ?

"ForkJoinPool.commonPool-worker-29" #1326 daemon prio=5 os_prio=0 tid=0x00007ff8d8054000 nid=0x2644 waiting on condition [0x00007ff87154a000] java.lang.Thread.State: WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)

Grep result from stack dump

- parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)
    - parking to wait for  <0x00000000804e10c8> (a java.util.concurrent.ForkJoinPool)

Answer 1

ForkJoinPool is used by the parallel stream operations. You should revise how you use the parallel() call on your streams (and - probably - rethink it, since waiting implies either blocking or synchronization, and neither should be used inside parallel streams).