WAITING at sun misc Unsafe park Native Method

Question

One of my applications hangs under some period of running under load  does anyone know what could cause such output in jstack    scheduler-5  prio 10 tid 0x00007f49481d0000 nid 0x2061 waiting on condition  0x00007f494e8d0000     java lang Thread State  WAITING  parking          at sun misc Unsafe park Native Method          - parking to wait for   lt 0x00000006ee117310 gt   a java util concurrent locks AbstractQueuedSynchronizer ConditionObject          at java util concurrent locks LockSupport park LockSupport java 186          at java util concurrent locks AbstractQueuedSynchronizer ConditionObject await AbstractQueuedSynchronizer java 2043          at java util concurrent ScheduledThreadPoolExecutor DelayedWorkQueue take ScheduledThreadPoolExecutor java 1085          at java util concurrent ScheduledThreadPoolExecutor DelayedWorkQueue take ScheduledThreadPoolExecutor java 807          at java util concurrent ThreadPoolExecutor getTask ThreadPoolExecutor java 1043          at java util concurrent ThreadPoolExecutor runWorker ThreadPoolExecutor java 1103          at java util concurrent ThreadPoolExecutor Worker run ThreadPoolExecutor java 603          at java lang Thread run Thread java 722    I am seeing this a lot in jstack output when it hangs   I heavily using Spring  Async  amp  maps  synchronized maps  amp  ehcache   What is interesting this only happens on one of app instances  Two others are running perfectly fine  What else I could investigate to get more details in such case   I found this post https   stackoverflow com questions 23992787 parking-to-wait-for-0xd8cf0070-a-java-util-concurrent-locks-abstractqueueds but it is not very useful in my case

User · Accepted Answer

unsafe park is pretty much the same as thread wait  except that it s using architecture specific code  thus the reason it s  unsafe    unsafe is not made available publicly  but is used within java internal libraries where architecture specific code would offer significant optimization benefits  It s used a lot for thread pooling   So  to answer your question  all the thread is doing is waiting for something  it s not really using any CPU  Considering that your original stack trace shows that you re using a lock I would assume a deadlock is going on in your case   Yes I know you have almost certainly already solved this issue by now  However  you re one of the top results if someone googles sun misc unsafe park  I figure answering the question may help others trying to understand what this method that seems to be using all their CPU is

User · Answer

I had a similar issue  and following previous answers  thanks    I was able to search and find how to handle correctly the ThreadPoolExecutor terminaison   In my case  that just fix my progressive increase of similar blocked threads    I ve used ExecutorService  awaitTermination x  TimeUnit  and ExecutorService  shutdownNow    if necessary  in my finally clause  For information  I ve used the following commands to detect thread count  amp  list locked threads   ps -u javaAppuser -L wc -l  jcmd  ps -C java -o pid   Thread print    threadPrintDayA log  jcmd  ps -C java -o pid   Thread print    threadPrintDayAPlusOne log  cat threadPrint  log  grep  pool-  wc -l

User · Answer

From the stack trace it s clear that  the ThreadPoolExecutor   Worker thread started and it s waiting for the task to be available on the BlockingQueue DelayedWorkQueue  to pick the task and execute So this thread will be in WAIT status only as long as get a SIGNAL from the publisher thread

[java] WAITING at sun.misc.Unsafe.park(Native Method)

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