Thread Dump

References:

从Thead Dump找出Java线程所对应的OS进行或线程，以能在OS层面观察该线程(CPU/Memory)

从Java Thread到OS Thread

./jstack -l <PID_OF_JAVA>

上面命令的输出就是Java虚拟机中的所有线程信息。对于每一个线程，你可以看到他都有一个nid(native thread id)，代表的就是系统的进程ID。我们可以看到，下面的输出中，线程"pool-30-thread-10"的nid是0x47c3=18371, 你可以在OS层面，去观察进程18371的信息和状态。

2017-02-22 13:05:18
Full thread dump Java HotSpot(TM) Server VM (25.111-b14 mixed mode):

"Attach Listener" #330 daemon prio=9 os_prio=0 tid=0x08330000 nid=0x3a24 waiting on condition [0x00000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
        - None

"pool-30-thread-10" #321 prio=5 os_prio=0 tid=0x0a9ac000 nid=0x47c3 waiting on condition [0xc5a74000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0xd89e1e10> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

   Locked ownable synchronizers:
        - None

观察进程18371的信息，常见的方法是用top或者/proc/<pid>/status

top -p 18371

cat /proc/18371/status
Name:   java
State:  S (sleeping)
Tgid:   22904
Ngid:   0
Pid:    18371
PPid:   1
TracerPid:      0
Uid:    0       0       0       0
Gid:    0       0       0       0
FDSize: 512
...

从OS进程到Java Thread

假设我们只知道进程号18371, 然后去看/proc/18371/status, 我们会看到Name: java, Tgid: 22904，22904可能就是JVM的主进程号。

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