Java Thread Pools and their Thread Dumps

When analysing a thead dump, if the thread is created with a custom thread name, we can easily trace it to where the thread pool is created by the unique thread name.

Otherwise, we will have to guess which type of thread pool is created from the stack trace, and then search the usage of creation methods like newCachedThreadPool, newSingleThreadScheduledExecutor, newScheduledThreadPool, or newCachedThreadPool.

When using Executors.newCachedThreadPool on JDK 6:

"pool-1-thread-2" prio=5 tid=7ffb30143000 nid=0x117fde000 waiting on condition [117fdd000]
   java.lang.Thread.State: TIMED_WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <7f310c388> (a java.util.concurrent.SynchronousQueue$TransferStack)
    at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:196)
    at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:424)
    at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:323)
    at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:874)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:945)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
    at java.lang.Thread.run(Thread.java:680)

When using Executors.newCachedThreadPool on JDK 7:

"pool-1-thread-2" prio=5 tid=0x00007f90b38c9800 nid=0x5603 waiting on condition [0x000000016cb92000]
   java.lang.Thread.State: TIMED_WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x000000014c55bbd8> (a java.util.concurrent.SynchronousQueue$TransferStack)
 at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:226)
 at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
 at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:359)
 at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:942)
 at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1043)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1103)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
 at java.lang.Thread.run(Thread.java:722)

When using Executors.newScheduledThreadPool(numOfCoreThreads) on JDK 6:

"pool-3-thread-1" prio=6 tid=0x4a5cc000 nid=0xc810 waiting on condition [0x4c96f000]
   java.lang.Thread.State: TIMED_WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x0934ccc8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
 at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:196)
 at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2025)
 at java.util.concurrent.DelayQueue.take(DelayQueue.java:164)
 at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:609)
 at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:602)
 at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
 at java.lang.Thread.run(Thread.java:662)

When using Executors.newScheduledThreadPool(numOfCoreThreads) on JDK 7:

"pool-1-thread-1" prio=5 tid=0x00007f8075802000 nid=0x5503 waiting on condition [0x00000001610ed000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x0000000140bbc108> (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$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1079)
 at java.util.concurrent.ScheduledThreadPoolExecutor$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)

When using Executors.newSingleThreadScheduledExecutor on JDK 6:

"pool-1-thread-1" prio=5 tid=7ff0fe159800 nid=0x11442e000 waiting on condition [11442d000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <7f310c8c0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1987)
    at java.util.concurrent.DelayQueue.take(DelayQueue.java:160)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:609)
    at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:602)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
    at java.lang.Thread.run(Thread.java:680)

When using Executors.newSingleThreadScheduledExecutor on JDK 7:

"pool-1-thread-1" prio=5 tid=0x00007ff7fb0aa000 nid=0x5503 waiting on condition [0x0000000169c4d000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x000000014971c208> (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$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1079)
 at java.util.concurrent.ScheduledThreadPoolExecutor$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)

When using Executors.newFixedThreadPool on JDK 6:

"pool-1-thread-2" prio=5 tid=7ff7c4854000 nid=0x118682000 waiting on condition [118681000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <7f44c0048> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
 at java.util.concurrent.locks.LockSupport.park(LockSupport.java:156)
 at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1987)
 at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:399)
 at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:947)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
 at java.lang.Thread.run(Thread.java:680)

When using Executors.newFixedThreadPool on JDK 7:

"pool-1-thread-1" prio=5 tid=0x00007fb3b4070000 nid=0x5503 waiting on condition [0x000000016c6bf000]
   java.lang.Thread.State: WAITING (parking)
 at sun.misc.Unsafe.park(Native Method)
 - parking to wait for  <0x000000014c18b888> (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.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
 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)