WAITING at sun.misc.Unsafe.park(Native Method) <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$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) </code></pre> <p>I am seeing this a lot in jstack output when it hangs.</p> <p>I heavily using Spring @Async &amp; maps, synchronized maps &amp; ehcache.</p> <p>What is interesting this only happens on one of app instances. Two others are running perfectly fine. What else I could investigate to get more details in such case?</p> <p>I found this post <a href="http://stackoverflow.com/questions/23992787/parking-to-wait-for-0xd8cf0070-a-java-util-concurrent-locks-abstractqueueds">- parking to wait for &lt;0xd8cf0070&gt; (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)</a> but it is not very useful in my case.</p>