title: WAITING at sun.misc.Unsafe.park(Native Method)
body: <p>One of my applications hangs under some period of running under load, does anyone know what could cause such output in jstack:</p>
  
  <pre><code>"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)
  </code></pre>
  
  <p>I am seeing this a lot in jstack output when it hangs.</p>
  
  <p>I heavily using Spring @Async &amp; maps, synchronized maps &amp; ehcache.</p>
  
  <p>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?</p>
  
  <p>I found this post <a href="https://stackoverflow.com/questions/23992787/parking-to-wait-for-0xd8cf0070-a-java-util-concurrent-locks-abstractqueueds">https://stackoverflow.com/questions/23992787/parking-to-wait-for-0xd8cf0070-a-java-util-concurrent-locks-abstractqueueds</a> but it is not very useful in my case.</p>