Java線程和多線程（八）——Thread Dump

Java的Thread Dump就是列出JVM中所有激活狀態的線程。

Java Thread Dump

Java Thread Dump在分析應用性能瓶頸和死鎖的時候，是非常有效的。

下面將介紹多種不同的方式來獲取Java程序的Thread Dump信息。這些指令在*nix型的操作系統下是有效的，但是在Windows下面，採取的方式會有一些不同。（主要是Pid信息獲取不太一致，可通過任務管理器獲取）

VisualVM Profiler：如果開發者需要分析程序變慢的原因，那麼必然要使用profiler。我們可以通過VisulaVM Profiler工具很容易的從運行的線程獲取Thread Dump。你所需要的就是右鍵運行的進行，然後點擊Thread Dump來獲得這個信息。
jstack：Java本身就自帶的jstack工具，我們可以通過Java線程來直接生成Thread Dump。
1. 受限找到Java進程的PID，可以通過ps -eaf | grep java命令來獲取。
2. 然後運行jstack工具，jstack PID來生成Thread Dump到控制檯，當然，也可以通過重定向，將Thread Dump信息的輸出通過命令jstack PID >> thread.dump寫入thread.dump這個文本當中。
我們可以通過kill -3 PID命令來生成Thread Dump信息。這種方式和其它的生成Thread Dump的方式略有不同，當執行了kill命令的時候，Thread Dump信息會直接輸出到控制檯。所以，如果Java程序的System.out是控制檯的話，Thread Dump的信息就會打印到控制檯。如果Java的程序時一個Tomcat的服務程序，System.out將變成catalina.out文件，那時，Thread Dump會打印到catalina.out這個文件之中。
Java 8引入了jcmd工具箱，開發者如果使用的是Java 8或者更高的版本的話，可以用之來替換掉jstack。命令行與jstack很類似：jcmd PID Thread.print。

上面的四種方式都可以用來在Java中生成Thread Dump的信息。通常，我推薦使用jstack或者jcmd命令來生成Thread Dump信息來分析。當然，無論你使用什麼樣的方式，最後的Thread Dump的信息都是一樣的。

Java Thread Dump舉例

我將自己寫的一個Tomcat程序運行Thread Dump，結果如下：

$ jcmd 4428 Thread.print
4428:
2016-09-27 22:42:29
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.65-b01 mixed mode):

"ajp-nio-8009-AsyncTimeout" #39 daemon prio=5 os_prio=0 tid=0x000000001d4c4000 nid=0x34c4 waiting on condition [0x000000002ca1f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.coyote.AbstractProtocol$AsyncTimeout.run(AbstractProtocol.java:1080)
        at java.lang.Thread.run(Thread.java:745)

"ajp-nio-8009-Acceptor-0" #38 daemon prio=5 os_prio=0 tid=0x000000001d4c6800 nid=0x34c0 runnable [0x000000002c91f000]
   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 <0x0000000080b2bfb0> (a java.lang.Object)
        at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:508)
        at java.lang.Thread.run(Thread.java:745)

"ajp-nio-8009-ClientPoller-1" #37 daemon prio=5 os_prio=0 tid=0x000000001d4c3800 nid=0x34bc runnable [0x000000002c81e000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x00000000829ecd28> (a sun.nio.ch.Util$2)
        - locked <0x00000000829ecd18> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000829ecba8> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:843)
        at java.lang.Thread.run(Thread.java:745)

"ajp-nio-8009-ClientPoller-0" #36 daemon prio=5 os_prio=0 tid=0x000000001d4c5800 nid=0x34b8 runnable [0x000000002b72f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x00000000829ee720> (a sun.nio.ch.Util$2)
        - locked <0x00000000829ee710> (a java.util.Collections$UnmodifiableSet)
        - locked <0x00000000829ee5a0> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:843)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8080-AsyncTimeout" #35 daemon prio=5 os_prio=0 tid=0x000000001d4c1000 nid=0x34b4 waiting on condition [0x000000002b62f000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.coyote.AbstractProtocol$AsyncTimeout.run(AbstractProtocol.java:1080)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8080-Acceptor-0" #34 daemon prio=5 os_prio=0 tid=0x000000001d4c2800 nid=0x34b0 runnable [0x000000002b52f000]
   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 <0x0000000080b30a30> (a java.lang.Object)
        at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:508)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8080-ClientPoller-1" #33 daemon prio=5 os_prio=0 tid=0x000000001d4c2000 nid=0x34ac runnable [0x000000002b1de000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x0000000082896118> (a sun.nio.ch.Util$2)
        - locked <0x0000000082896108> (a java.util.Collections$UnmodifiableSet)
        - locked <0x0000000082895f98> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:843)
        at java.lang.Thread.run(Thread.java:745)

"http-nio-8080-ClientPoller-0" #32 daemon prio=5 os_prio=0 tid=0x000000001d4c0800 nid=0x34a8 runnable [0x000000002b0de000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x0000000082896af8> (a sun.nio.ch.Util$2)
        - locked <0x0000000082896ae8> (a java.util.Collections$UnmodifiableSet)
        - locked <0x0000000082896978> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:843)
        at java.lang.Thread.run(Thread.java:745)

"ContainerBackgroundProcessor[StandardEngine[Catalina]]" #31 daemon prio=5 os_prio=0 tid=0x000000001f3d8800 nid=0x34a4 waiting on condition [0x0000000029fce000]
   java.lang.Thread.State: TIMED_WAITING (sleeping)
        at java.lang.Thread.sleep(Native Method)
        at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1340)
        at java.lang.Thread.run(Thread.java:745)

"pool-2-thread-1" #30 prio=5 os_prio=0 tid=0x000000001f3dc800 nid=0x3498 waiting on condition [0x00000000288df000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000082753eb0> (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 java.lang.Thread.run(Thread.java:745)

"Timer-0" #29 daemon prio=5 os_prio=0 tid=0x000000001f3d6000 nid=0x3494 in Object.wait() [0x000000002856f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at java.util.TimerThread.mainLoop(Timer.java:552)
        - locked <0x0000000082751430> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Timer.java:505)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_QuartzSchedulerThread" #28 prio=5 os_prio=0 tid=0x000000001f3dd000 nid=0x3490 in Object.wait() [0x000000002846e000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.core.QuartzSchedulerThread.run(QuartzSchedulerThread.java:410)
        - locked <0x0000000082751b28> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-10" #27 prio=5 os_prio=0 tid=0x000000001f3d7800 nid=0x348c in Object.wait() [0x000000002826f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082717950> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-9" #26 prio=5 os_prio=0 tid=0x000000001f3da000 nid=0x3488 in Object.wait() [0x000000002816f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082717618> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-8" #25 prio=5 os_prio=0 tid=0x000000001f3db800 nid=0x3484 in Object.wait() [0x000000002806f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x00000000827172e0> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-7" #24 prio=5 os_prio=0 tid=0x000000001f3d9000 nid=0x3480 in Object.wait() [0x0000000027f6f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082716fa8> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-6" #23 prio=5 os_prio=0 tid=0x000000001f3db000 nid=0x347c in Object.wait() [0x0000000027e6e000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082716c70> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-5" #22 prio=5 os_prio=0 tid=0x000000001f3d7000 nid=0x3478 in Object.wait() [0x0000000027d6f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082716938> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-4" #21 prio=5 os_prio=0 tid=0x000000002107b800 nid=0x3474 in Object.wait() [0x0000000027c6f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082716600> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-3" #20 prio=5 os_prio=0 tid=0x0000000023019000 nid=0x3470 in Object.wait() [0x0000000027b6f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x000000008270fb40> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-2" #19 prio=5 os_prio=0 tid=0x000000001f6a4000 nid=0x346c in Object.wait() [0x000000002721f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x00000000827162b0> (a java.lang.Object)

"org.springframework.scheduling.quartz.SchedulerFactoryBean#0_Worker-1" #18 prio=5 os_prio=0 tid=0x000000001a75a800 nid=0x3468 in Object.wait() [0x000000002014f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:568)
        - locked <0x0000000082715f78> (a java.lang.Object)

"NioBlockingSelector.BlockPoller-2" #15 daemon prio=5 os_prio=0 tid=0x0000000019d0b000 nid=0x2150 runnable [0x000000001b59e000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x0000000080a8c5c8> (a sun.nio.ch.Util$2)
        - locked <0x0000000080a8c5b8> (a java.util.Collections$UnmodifiableSet)
        - locked <0x0000000080a8c448> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:341)

"NioBlockingSelector.BlockPoller-1" #14 daemon prio=5 os_prio=0 tid=0x0000000019d09000 nid=0x890 runnable [0x000000001b49f000]
   java.lang.Thread.State: RUNNABLE
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(WindowsSelectorImpl.java:296)
        at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(WindowsSelectorImpl.java:278)
        at sun.nio.ch.WindowsSelectorImpl.doSelect(WindowsSelectorImpl.java:159)
        at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
        - locked <0x0000000080b2d2f8> (a sun.nio.ch.Util$2)
        - locked <0x0000000080b2d2e8> (a java.util.Collections$UnmodifiableSet)
        - locked <0x0000000080b2d188> (a sun.nio.ch.WindowsSelectorImpl)
        at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
        at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:341)

"GC Daemon" #13 daemon prio=2 os_prio=-2 tid=0x0000000019e8d800 nid=0x27fc in Object.wait() [0x000000001b17f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000080c322d0> (a sun.misc.GC$LatencyLock)
        at sun.misc.GC$Daemon.run(GC.java:117)
        - locked <0x0000000080c322d0> (a sun.misc.GC$LatencyLock)

"Service Thread" #11 daemon prio=9 os_prio=0 tid=0x0000000018c19000 nid=0x2a78 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" #10 daemon prio=9 os_prio=2 tid=0x0000000018bc2800 nid=0x11b8 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #9 daemon prio=9 os_prio=2 tid=0x0000000018bc1800 nid=0x1f90 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #8 daemon prio=9 os_prio=2 tid=0x0000000018bbf800 nid=0x3288 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Event Helper Thread" #7 daemon prio=10 os_prio=0 tid=0x0000000018bb2800 nid=0x339c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"JDWP Transport Listener: dt_socket" #6 daemon prio=10 os_prio=0 tid=0x0000000018ba6800 nid=0x1628 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x00000000175cd800 nid=0x1790 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001761e000 nid=0xa24 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000002998000 nid=0xb94 in Object.wait() [0x000000001893f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
        - locked <0x000000008051aa40> (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=2 tid=0x000000000298f000 nid=0x5cc in Object.wait() [0x000000001883f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157)
        - locked <0x00000000800cce68> (a java.lang.ref.Reference$Lock)

"main" #1 prio=5 os_prio=0 tid=0x000000000240e000 nid=0x2478 runnable [0x000000000289e000]
   java.lang.Thread.State: RUNNABLE
        at java.net.DualStackPlainSocketImpl.accept0(Native Method)
        at java.net.DualStackPlainSocketImpl.socketAccept(DualStackPlainSocketImpl.java:131)
        at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)
        at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:199)
        - locked <0x0000000082a8afe0> (a java.net.SocksSocketImpl)
        at java.net.ServerSocket.implAccept(ServerSocket.java:545)
        at java.net.ServerSocket.accept(ServerSocket.java:513)
        at org.apache.catalina.core.StandardServer.await(StandardServer.java:446)
        at org.apache.catalina.startup.Catalina.await(Catalina.java:737)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:683)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:351)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:485)

"VM Thread" os_prio=2 tid=0x0000000017587000 nid=0x1aec runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00000000028b7000 nid=0x1ea0 runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00000000028b8800 nid=0x19ac runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00000000028ba000 nid=0x2de8 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00000000028bd000 nid=0x540 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x0000000018c46000 nid=0x240c waiting on condition

JNI global references: 6164

Thread Dump會列出全部的線程，每個條目都包含如下的信息：

Thread Name：線程的名字
Thread Priority：線程的優先級
Thread ID：代表線程的ID
Thread Status：表示線程的狀態，舉例來說就是RUNNABLE，WAITING，BLOCKED等等，當在分析死鎖的時候，可以查看阻塞的線程和被請求的資源。
Thread CallStack：提供一個線程至關重要的堆棧信息。這也是我們可以看到線程獲取的鎖和是否在等待鎖等信息。

通過上面這些信息，就能夠看到一些程序的線程細節，當程序有一些問題之類，就可以從中找到真正影響性能的地方。

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