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I have a threaddump of an app which showed 3 threads like below.
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"http-443-11" daemon prio=10 tid=0x00000000473bc800 nid=0x3590 waiting on condition [0x0000000061818000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000007612a3880> (a java.util.concurrent.Semaphore$NonfairSync)
"http-443-4" daemon prio=10 tid=0x00000000451f6000 nid=0x243a waiting on condition [0x0000000055354000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000007612a3880> (a java.util.concurrent.Semaphore$NonfairSync)
"http-443-7" daemon prio=10 tid=0x000000004602e000 nid=0x2974 waiting on condition [0x000000005e6e7000]
java.lang.Thread.State: WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000007612a3880> (a java.util.concurrent.Semaphore$NonfairSync)
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What is the significance of the "waiting on condition []" ? What does the number in the [] signifiy ?
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Runnable: Means a thread is currently executing. Blocked: The thread is waiting for a lock to be released. This happens when entering a synchronized block, for instance. Waiting / Timed_waiting: The thread is waiting for something to happen.
The state "waiting on condition" means that the thread is waiting on an internal VM condition variable. These are not Java objects and so there is no means to identify them.
A thread in the waiting state is waiting for another thread to perform a particular action. For example, a thread that has called Object. wait() on an object is waiting for another thread to call Object. notify() or Object. notifyAll() on that object.
You can do thread dumps whenever you see fit to analyse anything to do with thread lock contention, deadlock detection, system resource contention, ... This is why there are tools to facilitate thread dump whenever we see fit, not only after a JVM crash.
In the thread stack we can see that threads are daemon threads and are waiting for task to come. Since these threads are created on JVM startup , they dont get killed unless JVM exits or any non daemon thread i not running, thus they wait for tasks to come. Say Garbage collection thread is a daemoon thread which might not be running all the time, it could be in waiting state.
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