jvm（java虚拟机）线程堆栈jstack（2）

jstack是java虚拟机自带的一种堆栈查看工具。主要目的是定位线程出现长时间停顿的原因，如线程间死锁、死循环、请求外部资源导致的长时间等待等。

jstack -help
Usage:jstack [-l] <pid>(to connect to running process)jstack -F [-m] [-l] <pid>(to connect to a hung process)jstack [-m] [-l] <executable> <core>(to connect to a core file)jstack [-m] [-l] [server_id@]<remote server IP or hostname>(to connect to a remote debug server)Options:-F  to force a thread dump. Use when jstack <pid> does not respond (process is hung)-m  to print both java and native frames (mixed mode)-l  long listing. Prints additional information about locks-h or -help to print this help message

1. 线程堆栈状态

以下是一个线程的堆栈输出结果：

"http-nio-8080-exec-10" #80 daemon prio=5 os_prio=0 tid=0x000000002e33e000 nid=0x1a80 waiting on condition [0x00000000369df000]java.lang.Thread.State: WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for  <0x00000006c1e418c8> (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:146)at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)at org.apache.tomcat.util.threads.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1114)at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1176)at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Thread.java:748)

2. 调用修饰

2.1 locked

locked <地址> 目标：使用synchronized申请对象锁成功，监视器的拥有者。

通过synchronized关键字，成功获取到了对象的锁，成为监视器的拥有者，在临界区内操作。对象锁是可以线程重入的。

2.2 waiting to lock

waiting to lock <地址> 目标：使用synchronized申请对象锁未成功，在进入区等待。

通过synchronized关键字，没有获取到了对象的锁，线程在监视器的进入区等待。在调用栈顶出现，线程状态为Blocked。

2.3 waiting on

waiting on <地址> 目标：使用synchronized申请对象锁成功后，释放锁幵在等待区等待。

通过synchronized关键字，成功获取到了对象的锁后，调用了wait方法,进入对象的等待区等待。在调用栈顶出现,线程状态为WAITING或TIMED_WATING。

2.4 parking to wait for

parking to wait for <地址> 目标

park是基本的线程阻塞原语，不通过监视器在对象上阻塞。随concurrent包会出现的新的机制。

2. 线程状态产生的原因

runnable：状态一般为RUNNABLE。

in Object.wait()：等待区等待,状态为WAITING或TIMED_WAITING。

waiting for monitor entry：进入区等待,状态为BLOCKED。

waiting on condition：等待区等待、被park。

sleeping：休眠的线程，调用了Thread.sleep()。

3. 线程Dump的分析

1. 进入区等待

"d&a-3588" daemon waiting for monitor entry [0x000000006e5d5000]
java.lang.Thread.State: BLOCKED (on object monitor)
at com.jiuqi.dna.bap.authority.service.UserService$LoginHandler.handle()
- waiting to lock <0x0000000602f38e90> (a java.lang.Object)
at com.jiuqi.dna.bap.authority.service.UserService$LoginHandler.handle()

线程状态BLOCKED,线程动作waiting for monitor entry,调用修饰waiting to lock总是一起出现。表示在代码级别已经存在冲突的调用。必然有问题的代码,需要尽可能减少其发生。

2. 同步块阻塞

"blockee-11" waiting for monitor entry
java.lang.Thread.State: BLOCKED (on object monitor)
at com.jiuqi.hcl.javadump.Blocker$2.run(Blocker.java:41)
- waiting to lock <0x00000000eb8eff68> (a java.lang.Object)
"blockee-86" waiting for monitor entry
java.lang.Thread.State: BLOCKED (on object monitor)
at com.jiuqi.hcl.javadump.Blocker$2.run(Blocker.java:41)
- waiting to lock <0x00000000eb8eff68> (a java.lang.Object)

3. 线程状态为RUNNABLE

持续运行的IO IO操作是可以以RUNNABLE状态达成阻塞。例如:数据库死锁、网络读写。格外注对IO线程的真实状态的分析。一般来说,被捕捉到RUNNABLE的IO调用,都是有问题的。

线程状态为RUNNABLE。调用栈在SocketInputStream或SocketImpl上,socketRead0等方法。调用栈包含了jdbc相关的包。很可能发生了数据库死锁

4. 线程调度的休眠

4.1 正常的线程池等待

"http-nio-8080-exec-3" #68 daemon prio=5 os_prio=0 tid=0x000000002e335800 nid=0x85a4 waiting on condition [0x000000003510e000]java.lang.Thread.State: WAITING (parking)at sun.misc.Unsafe.park(Native Method)- parking to wait for  <0x00000006c1e418c8> (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:146)at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)at org.apache.tomcat.util.threads.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1114)at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1176)at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Thread.java:748)

4.2 可疑的线程等待（重点关注）

wait on monitor entry：被阻塞的,肯定有问题

runnable ：注意IO线程

in Object.wait()：注意非线程池等待