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arthas/_sources/thread.md.txt

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thread
===
> 查看当前线程信息,查看线程的堆栈
### 参数说明
|参数名称|参数说明|
|---:|:---|
|*id*|线程id|
|[n:]|指定最忙的前N个线程并打印堆栈|
|[b]|找出当前阻塞其他线程的线程|
|[i `<value>`]|指定cpu占比统计的采样间隔单位为毫秒|
> cpu占比是如何统计出来的
> 这里的cpu统计的是一段采样间隔内当前JVM里各个线程所占用的cpu时间占总cpu时间的百分比。其计算方法为
> 首先进行一次采样获得所有线程的cpu的使用时间(调用的是`java.lang.management.ThreadMXBean#getThreadCpuTime`这个接口)然后睡眠一段时间默认100ms可以通过`-i`参数指定然后再采样一次最后得出这段时间内各个线程消耗的cpu时间情况最后算出百分比。
> 注意: 这个统计也会产生一定的开销JDK这个接口本身开销比较大因此会看到as的线程占用一定的百分比为了降低统计自身的开销带来的影响可以把采样间隔拉长一些比如5000毫秒。
> 如果想看从Java进程启动开始到现在的cpu占比情况可以使用[show-busy-java-threads](https://github.com/oldratlee/useful-scripts/blob/master/docs/java.md#-show-busy-java-threads)这个脚本
### 使用参考
#### 支持一键展示当前最忙的前N个线程并打印堆栈
```shell
$ thread -n 3
"as-command-execute-daemon" Id=29 cpuUsage=75% RUNNABLE
at sun.management.ThreadImpl.dumpThreads0(Native Method)
at sun.management.ThreadImpl.getThreadInfo(ThreadImpl.java:440)
at com.taobao.arthas.core.command.monitor200.ThreadCommand$1.action(ThreadCommand.java:58)
at com.taobao.arthas.core.command.handler.AbstractCommandHandler.execute(AbstractCommandHandler.java:238)
at com.taobao.arthas.core.command.handler.DefaultCommandHandler.handleCommand(DefaultCommandHandler.java:67)
at com.taobao.arthas.core.server.ArthasServer$4.run(ArthasServer.java:276)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Number of locked synchronizers = 1
- java.util.concurrent.ThreadPoolExecutor$Worker@6cd0b6f8
"as-session-expire-daemon" Id=25 cpuUsage=24% TIMED_WAITING
at java.lang.Thread.sleep(Native Method)
at com.taobao.arthas.core.server.DefaultSessionManager$2.run(DefaultSessionManager.java:85)
"Reference Handler" Id=2 cpuUsage=0% WAITING on java.lang.ref.Reference$Lock@69ba0f27
at java.lang.Object.wait(Native Method)
- waiting on java.lang.ref.Reference$Lock@69ba0f27
at java.lang.Object.wait(Object.java:503)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)
```
#### 当没有参数时,显示所有线程的信息。
```shell
$ thread
Threads Total: 16, NEW: 0, RUNNABLE: 7, BLOCKED: 0, WAITING: 5, TIMED_WAITING: 4, TERMINATED: 0
ID NAME GROUP PRIORITY STATE %CPU TIME INTERRUPTE DAEMON
30 as-command-execute-daemon system 9 RUNNABLE 72 0:0 false true
23 as-session-expire-daemon system 9 TIMED_WAIT 27 0:0 false true
22 Attach Listener system 9 RUNNABLE 0 0:0 false true
11 pool-2-thread-1 main 5 TIMED_WAIT 0 0:0 false false
12 Thread-2 main 5 RUNNABLE 0 0:0 false true
13 pool-3-thread-1 main 5 TIMED_WAIT 0 0:0 false false
25 as-selector-daemon system 9 RUNNABLE 0 0:0 false true
14 Thread-3 main 5 TIMED_WAIT 0 0:0 false false
26 pool-5-thread-1 system 5 WAITING 0 0:0 false false
15 Thread-4 main 5 RUNNABLE 0 0:0 false false
1 main main 5 WAITING 0 0:2 false false
2 Reference Handler system 10 WAITING 0 0:0 false true
3 Finalizer system 8 WAITING 0 0:0 false true
4 Signal Dispatcher system 9 RUNNABLE 0 0:0 false true
20 NonBlockingInputStreamThread main 5 WAITING 0 0:0 false true
21 Thread-8 main 5 RUNNABLE 0 0:0 false true
```
#### thread id 显示指定线程的运行堆栈
```shell
$ thread 1
"main" Id=1 WAITING on java.util.concurrent.CountDownLatch$Sync@29fafb28
at sun.misc.Unsafe.park(Native Method)
- waiting on java.util.concurrent.CountDownLatch$Sync@29fafb28
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)
at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)
```
#### thread -b, 找出当前阻塞其他线程的线程
有时候我们发现应用卡住了, 通常是由于某个线程拿住了某个锁, 并且其他线程都在等待这把锁造成的。 为了排查这类问题, arthas提供了`thread -b` 一键找出那个罪魁祸首。
```bash
$ thread -b
"http-bio-8080-exec-4" Id=27 TIMED_WAITING
at java.lang.Thread.sleep(Native Method)
at test.arthas.TestThreadBlocking.doGet(TestThreadBlocking.java:22)
- locked java.lang.Object@725be470 <---- but blocks 4 other threads!
at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at test.filter.TestDurexFilter.doFilter(TestDurexFilter.java:46)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at com.taobao.tomcat.valves.ContextLoadFilterValve$FilterChainAdapter.doFilter(ContextLoadFilterValve.java:191)
at com.taobao.eagleeye.EagleEyeFilter.doFilter(EagleEyeFilter.java:81)
at com.taobao.tomcat.valves.ContextLoadFilterValve.invoke(ContextLoadFilterValve.java:150)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:429)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1085)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
- locked org.apache.tomcat.util.net.SocketWrapper@7127ee12
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Number of locked synchronizers = 1
- java.util.concurrent.ThreadPoolExecutor$Worker@31a6493e
```
> 注意, 目前只支持找出synchronized关键字阻塞住的线程 如果是`java.util.concurrent.Lock` 目前还不支持。
#### thread -i, 指定采样时间间隔
```bash
$ thread -n 3 -i 1000
"as-command-execute-daemon" Id=4759 cpuUsage=23% RUNNABLE
at sun.management.ThreadImpl.dumpThreads0(Native Method)
at sun.management.ThreadImpl.getThreadInfo(ThreadImpl.java:440)
at com.taobao.arthas.core.command.monitor200.ThreadCommand.processTopBusyThreads(ThreadCommand.java:133)
at com.taobao.arthas.core.command.monitor200.ThreadCommand.process(ThreadCommand.java:79)
at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.process(AnnotatedCommandImpl.java:96)
at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.access$100(AnnotatedCommandImpl.java:27)
at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:125)
at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:122)
at com.taobao.arthas.core.shell.system.impl.ProcessImpl$CommandProcessTask.run(ProcessImpl.java:332)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:756)
Number of locked synchronizers = 1
- java.util.concurrent.ThreadPoolExecutor$Worker@546aeec1
...
```