JVM tuning before the play of the JDK command line tools --- jstack

In JDK command line, usually the developer is certainly the most familiar java, javac, javap and other commonly used commands, but in the jdk / bin There are many other command-line tools that are used to monitor the state of the JVM run-time, Let's look at a detailed explanation of a few common tools and how to use.

jstack

jstack (JVM Stack Trace) for generating a snapshot of the virtual machine thread the current time. Thread is a snapshot of the current method of virtual machines each executing thread stack collection, the main purpose of generating a snapshot of the thread is the reason why long pause positioning threads appear, such as thread deadlocks, infinite loop, waiting for a request for a long time due to external resources so are a common cause of thread long pause. When the thread pause to view the call stack of each thread through jstack, you can know that is not responding thread in the end things done in the background, waiting for something or resources.

Command Format

jstack [option] LVMID

option parameters

• -F : When the normal response to the output request is not to force the output thread stack
• -l : In addition to the stack, display additional information about locks
• -m : If you call to the local method, you can display the C / C ++ stack

Examples

$ jstack -l 45995
2019-08-14 17:34:36
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.45-b02 mixed mode):

"Attach Listener" #46 daemon prio=9 os_prio=31 tid=0x00007fc62527e800 nid=0x6b07 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-10" #44 daemon prio=5 os_prio=31 tid=0x00007fc61f359000 nid=0x8a03 waiting on condition [0x0000700002fa3000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-9" #43 daemon prio=5 os_prio=31 tid=0x00007fc620475000 nid=0x8803 waiting on condition [0x0000700002ea0000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None

"http-bio-8082-exec-8" #42 daemon prio=5 os_prio=31 tid=0x00007fc61f002000 nid=0x8603 waiting on condition [0x0000700002d9d000]
   java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x00000006c04cdb28> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:104)
    at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:32)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

   Locked ownable synchronizers:
    - None
    ......