jstack如何确定java进程阻塞 jstack查看线程状态

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mob64ca13fe62db 2023-11-23 12:13:17

文章标签 jstack如何确定java进程阻塞堆栈多线程 java linux 文章分类 Java 后端开发

文章目录

用途
命令格式
查看占用 cpu 较高的线程
查看输出
统计线程数
死锁

用途

jstack 用于打印出给定的 java 进程 ID 的 Java 堆栈信息。

如果 java 程序崩溃生成文件，jstack 可以获得文件的堆栈信息，从而可以知道 java 程序是如何崩溃以及在程序出现问题的地方。另外， jstack 还可以附属到正在运行的 java 程序中，看到当时运行的 java 程序的堆栈信息。

命令格式

jstack [-l] <pid> # 连接活动线程
jstack -F [-m] [-l] <pid> # 连接阻塞线程
jstack [-m] [-l] <executable> <core> # 连接 dump 的文件
jstack [-m] [-l] [server_id@]<remote server IP or hostname> # 连接远程服务器

一些选项：

-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

查看占用 cpu 较高的线程

执行 top 命令，查看各个进程的 cpu 使用情况，默认按 cpu 使用率排序

top

jstack如何确定java进程阻塞 jstack查看线程状态_linux

可见 PID 为1的 java 进程占用了较多的 cpu 资源。

然后我们查看一下在此进程内 cpu 占用高的线程

top -Hp 1

jstack如何确定java进程阻塞 jstack查看线程状态_多线程_02

现在我们获取了该进程下所有线程的 ID，可以通过执行 jstack 对线程堆栈信息进行查看，不过在此之前，我们需要对线程 ID 做一个转换（十进制转十六进制）

printf "%x\n" 20
14

然后我们可以打印我们指定的线程的堆栈信息，该线程可以是占用 cpu 较高的线程，例如：

jstack 1 | grep 14 -A 30

"http-nio-8082-BlockPoller" #14 daemon prio=5 os_prio=0 tid=0x00007f8a7c6d4800 nid=0x14 runnable [0x00007f8a4bfe8000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
        at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
        at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x00000000ed878dd0> (a sun.nio.ch.Util$3)
        - locked <0x00000000ed878de0> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000ed878d88> (a sun.nio.ch.EPollSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:313)

具体信息分析如下：

http-nio-8082-BlockPoller：线程名
daemon：是否为守护线程
prio：我们为线程设置的优先级
os_prio：操作系统线程的优先级
tid：java中这个线程的 id
nid：这个线程对应的操作系统本地线程 id，每一个 java 线程都有一个对应的操作系统线程
runnable：目前线程的状态，runnable 表示线程处于可运行状态
java.lang.Thread.State: RUNNABLE：处于可运行状态

对 java.lang.Thread.State 的说明：表示一个 Thread 对象的状态

NEW：线程刚被创建，但还没有调用 start() 方法，jstack命令不会列出处于此状态的线程信息
RUNNABLE：表示线程是可运行的，而不是线程正在运行
BLOCKED：线程处于阻塞状态，一般是在等待获取锁
WAITING：等待状态，一个线程调用以下方法之一可能会导致等待状态：Object.wait 不指定超时时间 # java.lang.Thread.State: WAITING (on object monitor) / Thread.join with no timeout / LockSupport.park #java.lang.Thread.State: WAITING (parking)
TIMED_WAITING：线程等待指定的时间，可能调用了以下方法：Thread.sleep #java.lang.Thread.State: TIMED_WAITING (sleeping) / Object.wait 指定超时时间 #java.lang.Thread.State: TIMED_WAITING (on object monitor) / Thread.join with timeout / LockSupport.parkNanos #java.lang.Thread.State: TIMED_WAITING (parking) / LockSupport.parkUntil #java.lang.Thread.State: TIMED_WAITING (parking)
TERMINATED：线程终止

查看输出

jstack pid 命令查看当前 java 进程的堆栈状态。

jstack 1

2020-12-10 02:09:08
Full thread dump OpenJDK 64-Bit Server VM (25.111-b14 mixed mode):

"Attach Listener" #29 daemon prio=9 os_prio=0 tid=0x00007f8a58003800 nid=0x31 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DestroyJavaVM" #28 prio=5 os_prio=0 tid=0x00007f8a7c009800 nid=0x6 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"http-nio-8082-Acceptor" #26 daemon prio=5 os_prio=0 tid=0x00007f8a7c6e7000 nid=0x20 runnable [0x00007f8a4b3dc000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:422)
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:250)
        - locked <0x00000000ed8774b0> (a java.lang.Object)
        at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:461)
        at org.apache.tomcat.util.net.NioEndpoint.serverSocketAccept(NioEndpoint.java:73)
        at org.apache.tomcat.util.net.Acceptor.run(Acceptor.java:95)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8082-ClientPoller" #25 daemon prio=5 os_prio=0 tid=0x00007f8a7c762000 nid=0x1f runnable [0x00007f8a4b4dd000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
        at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
        at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x00000000ed8776e0> (a sun.nio.ch.Util$3)
        - locked <0x00000000ed8776f0> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000ed877698> (a sun.nio.ch.EPollSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:706)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8082-exec-10" #24 daemon prio=5 os_prio=0 tid=0x00007f8a7c789000 nid=0x1e waiting on condition [0x00007f8a4b5de000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-9" #23 daemon prio=5 os_prio=0 tid=0x00007f8a7c787800 nid=0x1d waiting on condition [0x00007f8a4b6df000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-8" #22 daemon prio=5 os_prio=0 tid=0x00007f8a7c75d800 nid=0x1c waiting on condition [0x00007f8a4b7e0000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-7" #21 daemon prio=5 os_prio=0 tid=0x00007f8a7c75c000 nid=0x1b waiting on condition [0x00007f8a4b8e1000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-6" #20 daemon prio=5 os_prio=0 tid=0x00007f8a7c704800 nid=0x1a waiting on condition [0x00007f8a4b9e2000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-5" #19 daemon prio=5 os_prio=0 tid=0x00007f8a7c4fc000 nid=0x19 waiting on condition [0x00007f8a4bae3000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-4" #18 daemon prio=5 os_prio=0 tid=0x00007f8a7c76a000 nid=0x18 waiting on condition [0x00007f8a4bbe4000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-3" #17 daemon prio=5 os_prio=0 tid=0x00007f8a7c53c800 nid=0x17 waiting on condition [0x00007f8a4bce5000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-2" #16 daemon prio=5 os_prio=0 tid=0x00007f8a7c6c1000 nid=0x16 waiting on condition [0x00007f8a4bde6000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-exec-1" #15 daemon prio=5 os_prio=0 tid=0x00007f8a7c708000 nid=0x15 waiting on condition [0x00007f8a4bee7000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed8778b0> (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:107)
        at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:33)
        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)

"http-nio-8082-BlockPoller" #14 daemon prio=5 os_prio=0 tid=0x00007f8a7c6d4800 nid=0x14 runnable [0x00007f8a4bfe8000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
        at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
        at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x00000000ed878dd0> (a sun.nio.ch.Util$3)
        - locked <0x00000000ed878de0> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000ed878d88> (a sun.nio.ch.EPollSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:313)

"container-0" #13 prio=5 os_prio=0 tid=0x00007f8a7c6b0800 nid=0x13 waiting on condition [0x00007f8a4c2e9000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.StandardServer.await(StandardServer.java:570)
        at org.springframework.boot.web.embedded.tomcat.TomcatWebServer$1.run(TomcatWebServer.java:179)

"Catalina-utility-2" #12 prio=1 os_prio=0 tid=0x00007f8a7c6ad800 nid=0x12 waiting on condition [0x00007f8a4cffd000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed660490> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
        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)

"Catalina-utility-1" #11 prio=1 os_prio=0 tid=0x00007f8a7c676000 nid=0x11 waiting on condition [0x00007f8a6cffe000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000ed660490> (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.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1088)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
        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)

"Service Thread" #7 daemon prio=9 os_prio=0 tid=0x00007f8a7c0d0800 nid=0xd runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f8a7c0ce000 nid=0xc waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f8a7c0cb800 nid=0xb waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f8a7c0c9800 nid=0xa runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f8a7c0a1000 nid=0x9 in Object.wait() [0x00007f8a8084a000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000ecde1e78> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
        - locked <0x00000000ecde1e78> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f8a7c09c800 nid=0x8 in Object.wait() [0x00007f8a8094b000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000ecde2030> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x00000000ecde2030> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"VM Thread" os_prio=0 tid=0x00007f8a7c095000 nid=0x7 runnable 

"VM Periodic Task Thread" os_prio=0 tid=0x00007f8a7c0d8000 nid=0xe waiting on condition 

JNI global references: 1072

jstack 命令生成的 thread dump 信息包含了 JVM 中所有存活的线程，我们可以隔段时间再执行一次 jstack 命令来获取 thread dump，比较两份 dump 是否存在区别。分析线程调用栈是否一直执行某方法，然后我们可以根据这个信息检查代码是否存在问题。

统计线程数

jstack -l 1 | grep 'java.lang.Thread.State' | wc -l
24

死锁

在 JAVA 5 中加强了对死锁的检测。线程 Dump 中可以直接报告出 Java 级别的死锁，例如：

Found one Java-level deadlock:

=============================

"Thread-1":

waiting to lock monitor 0x0003f334 (object 0x22c19f18, a java.lang.Object),

which is held by "Thread-0"

"Thread-0":

waiting to lock monitor 0x0003f314 (object 0x22c19f20, a java.lang.Object),

which is held by "Thread-1"

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