too many free threads in threads pool

[sam.gu]

There are a lot of free threads in jboss as 7 thread pool,the thread dump is below :

"thread_size-threads - 456" prio=6 tid=0x0000000025dff000 nid=0x20f0 waiting on condition [0x000000004b6ef000]

   java.lang.Thread.State: WAITING (parking)

  at sun.misc.Unsafe.park(Native Method)

  - parking to wait for  <0x0000000780520778> (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:1068)

  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)

  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

  at java.lang.Thread.run(Thread.java:724)

  at org.jboss.threads.JBossThread.run(JBossThread.java:122)

  Locked ownable synchronizers:

  - None

"thread_size-threads - 455" prio=6 tid=0x0000000025dfe000 nid=0x1b70 waiting on condition [0x000000004bf9e000]

   java.lang.Thread.State: WAITING (parking)

  at sun.misc.Unsafe.park(Native Method)

  - parking to wait for  <0x0000000780520778> (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:1068)

  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)

  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

  at java.lang.Thread.run(Thread.java:724)

  at org.jboss.threads.JBossThread.run(JBossThread.java:122)

   Locked ownable synchronizers:

  - None

     this thread is more than 400,but i have set the thread keeplive-time ,why it is't effect??

My thread pool config :

<subsystem xmlns="urn:jboss:domain:threads:1.1">

            <unbounded-queue-thread-pool name="thread_size">

                <max-threads count="500"/>

                <keepalive-time time="30" unit="seconds"/>

            </unbounded-queue-thread-pool>

        </subsystem>

<subsystem xmlns="urn:jboss:domain:web:1.4" default-virtual-server="default-host" native="false">

            <connector name="http" protocol="HTTP/1.1" scheme="http" socket-binding="http" executor="thread_size" max-connections="1000"/>

            <virtual-server name="default-host" enable-welcome-root="false">

                <alias name="localhost"/>

                <alias name="example.com"/>

            </virtual-server>

        </subsystem>