JVM調(diào)優(yōu)前戲之JDK命令行工具---jstack

Cristic 發(fā)布于2019-08-19 10:31 / 2747人閱讀

摘要：用于生成虛擬機(jī)當(dāng)前時(shí)刻的線程快照。線程快照就是當(dāng)前虛擬機(jī)內(nèi)每一條線程正在執(zhí)行的方法堆棧的集合，生成線程快照的主要目的就是定位線程出現(xiàn)長(zhǎng)時(shí)間停頓的原因，如線程死鎖死循環(huán)請(qǐng)求外部資源導(dǎo)致的長(zhǎng)時(shí)間等待等都是導(dǎo)致線程長(zhǎng)時(shí)間停頓的常見原因。

在JDK的命令行中，一般開發(fā)人員最耳熟能詳?shù)目隙ň褪莏ava,javac,javap等常用命令，不過在jdk/bin下還有許多其他的命令行工具，它們被用來監(jiān)測(cè)JVM運(yùn)行時(shí)的狀態(tài)，下面我們來詳細(xì)解讀一下幾個(gè)常用的工具以及如何使用。

jstack

jstack(JVM Stack Trace)用于生成虛擬機(jī)當(dāng)前時(shí)刻的線程快照。線程快照就是當(dāng)前虛擬機(jī)內(nèi)每一條線程正在執(zhí)行的方法堆棧的集合，生成線程快照的主要目的就是定位線程出現(xiàn)長(zhǎng)時(shí)間停頓的原因，如線程死鎖、死循環(huán)、請(qǐng)求外部資源導(dǎo)致的長(zhǎng)時(shí)間等待等都是導(dǎo)致線程長(zhǎng)時(shí)間停頓的常見原因。線程出現(xiàn)停頓的時(shí)候通過jstack來查看各個(gè)線程的調(diào)用堆棧，就可以知道沒有響應(yīng)的線程在后臺(tái)到底做了些什么事情，或者等待著什么資源。

命令格式

jstack [option] LVMID

option參數(shù)


-F : 當(dāng)正常輸出請(qǐng)求不被響應(yīng)時(shí)，強(qiáng)制輸出線程堆棧

-l : 除堆棧外，顯示關(guān)于鎖的附加信息

-m : 如果調(diào)用到本地方法的話，可以顯示C/C++的堆棧

示例

$ 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
    ......