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# thread
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[`thread`在线教程](https://arthas.aliyun.com/doc/arthas-tutorials.html?language=cn&id=command-thread)
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::: tip
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查看当前线程信息，查看线程的堆栈
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:::
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## 参数说明
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| 参数名称 | 参数说明 |
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| ------------: | :------------------------------------------------------ |
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| _id_ | 线程 id |
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| [n:] | 指定最忙的前 N 个线程并打印堆栈 |
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| [b] | 找出当前阻塞其他线程的线程 |
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| [i `<value>`] | 指定 cpu 使用率统计的采样间隔，单位为毫秒，默认值为 200 |
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| [--all] | 显示所有匹配的线程 |
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## cpu 使用率是如何统计出来的？
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这里的 cpu 使用率与 linux 命令`top -H -p <pid>` 的线程`%CPU`类似，一段采样间隔时间内，当前 JVM 里各个线程的增量 cpu 时间与采样间隔时间的比例。
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### 工作原理说明：
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- 首先第一次采样，获取所有线程的 CPU 时间(调用的是`java.lang.management.ThreadMXBean#getThreadCpuTime()`及`sun.management.HotspotThreadMBean.getInternalThreadCpuTimes()`接口)
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- 然后睡眠等待一个间隔时间（默认为 200ms，可以通过`-i`指定间隔时间）
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- 再次第二次采样，获取所有线程的 CPU 时间，对比两次采样数据，计算出每个线程的增量 CPU 时间
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- 线程 CPU 使用率 = 线程增量 CPU 时间 / 采样间隔时间 \* 100%
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::: warning
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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。
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:::
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::: tip
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另外一种查看 Java 进程的线程 cpu 使用率方法：可以使用[`show-busy-java-threads`](https://github.com/oldratlee/useful-scripts/blob/dev-2.x/docs/java.md#-show-busy-java-threads)这个脚本。
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:::
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## 使用参考
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### 支持一键展示当前最忙的前 N 个线程并打印堆栈：
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```shell
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$ thread -n 3
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"C1 CompilerThread0" [Internal] cpuUsage=1.63% deltaTime=3ms time=1170ms
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"arthas-command-execute" Id=23 cpuUsage=0.11% deltaTime=0ms time=401ms RUNNABLE
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at java.management@11.0.7/sun.management.ThreadImpl.dumpThreads0(Native Method)
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at java.management@11.0.7/sun.management.ThreadImpl.getThreadInfo(ThreadImpl.java:466)
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at com.taobao.arthas.core.command.monitor200.ThreadCommand.processTopBusyThreads(ThreadCommand.java:199)
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at com.taobao.arthas.core.command.monitor200.ThreadCommand.process(ThreadCommand.java:122)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.process(AnnotatedCommandImpl.java:82)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.access$100(AnnotatedCommandImpl.java:18)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:111)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:108)
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at com.taobao.arthas.core.shell.system.impl.ProcessImpl$CommandProcessTask.run(ProcessImpl.java:385)
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at java.base@11.0.7/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
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at java.base@11.0.7/java.util.concurrent.FutureTask.run(FutureTask.java:264)
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at java.base@11.0.7/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
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at java.base@11.0.7/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
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at java.base@11.0.7/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
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at java.base@11.0.7/java.lang.Thread.run(Thread.java:834)
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"VM Periodic Task Thread" [Internal] cpuUsage=0.07% deltaTime=0ms time=584ms
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```
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- 没有线程 ID，包含`[Internal]`表示为 JVM 内部线程，参考[dashboard](dashboard.md)命令的介绍。
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- `cpuUsage`为采样间隔时间内线程的 CPU 使用率，与[dashboard](dashboard.md)命令的数据一致。
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- `deltaTime`为采样间隔时间内线程的增量 CPU 时间，小于 1ms 时被取整显示为 0ms。
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- `time` 线程运行总 CPU 时间。
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注意：线程栈为第二采样结束时获取，不能表明采样间隔时间内该线程都是在处理相同的任务。建议间隔时间不要太长，可能间隔时间越大越不准确。
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可以根据具体情况尝试指定不同的间隔时间，观察输出结果。
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### 当没有参数时，显示第一页线程的信息
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默认按照 CPU 增量时间降序排列，只显示第一页数据。
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```shell
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$ thread
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Threads Total: 33, NEW: 0, RUNNABLE: 9, BLOCKED: 0, WAITING: 3, TIMED_WAITING: 4, TERMINATED: 0, Internal threads: 17
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ID NAME GROUP PRIORITY STATE %CPU DELTA_TIME TIME INTERRUPT DAEMON
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-1 C2 CompilerThread0 - -1 - 5.06 0.010 0:0.973 false true
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-1 C1 CompilerThread0 - -1 - 0.95 0.001 0:0.603 false true
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23 arthas-command-execute system 5 RUNNABLE 0.17 0.000 0:0.226 false true
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-1 VM Periodic Task Thread - -1 - 0.05 0.000 0:0.094 false true
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-1 Sweeper thread - -1 - 0.04 0.000 0:0.011 false true
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-1 G1 Young RemSet Sampling - -1 - 0.02 0.000 0:0.025 false true
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12 Attach Listener system 9 RUNNABLE 0.0 0.000 0:0.022 false true
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11 Common-Cleaner InnocuousThrea 8 TIMED_WAI 0.0 0.000 0:0.000 false true
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3 Finalizer system 8 WAITING 0.0 0.000 0:0.000 false true
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2 Reference Handler system 10 RUNNABLE 0.0 0.000 0:0.000 false true
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4 Signal Dispatcher system 9 RUNNABLE 0.0 0.000 0:0.000 false true
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15 arthas-NettyHttpTelnetBootstra system 5 RUNNABLE 0.0 0.000 0:0.029 false true
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22 arthas-NettyHttpTelnetBootstra system 5 RUNNABLE 0.0 0.000 0:0.196 false true
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24 arthas-NettyHttpTelnetBootstra system 5 RUNNABLE 0.0 0.000 0:0.038 false true
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16 arthas-NettyWebsocketTtyBootst system 5 RUNNABLE 0.0 0.000 0:0.001 false true
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17 arthas-NettyWebsocketTtyBootst system 5 RUNNABLE 0.0 0.000 0:0.001 false true
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```
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### thread --all, 显示所有匹配的线程
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显示所有匹配线程信息，有时需要获取全部 JVM 的线程数据进行分析。
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### thread id, 显示指定线程的运行堆栈
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```shell
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$ thread 1
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"main" Id=1 WAITING on java.util.concurrent.CountDownLatch$Sync@29fafb28
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at sun.misc.Unsafe.park(Native Method)
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- waiting on java.util.concurrent.CountDownLatch$Sync@29fafb28
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at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
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at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
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at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)
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at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)
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at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)
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```
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### thread -b, 找出当前阻塞其他线程的线程
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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。
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```bash
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$ thread -b
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"http-bio-8080-exec-4" Id=27 TIMED_WAITING
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at java.lang.Thread.sleep(Native Method)
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at test.arthas.TestThreadBlocking.doGet(TestThreadBlocking.java:22)
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- locked java.lang.Object@725be470 <---- but blocks 4 other threads!
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at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
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at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
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at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
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at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
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at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
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at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
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at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
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at test.filter.TestDurexFilter.doFilter(TestDurexFilter.java:46)
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at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
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at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
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at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
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at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
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at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
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at com.taobao.tomcat.valves.ContextLoadFilterValve$FilterChainAdapter.doFilter(ContextLoadFilterValve.java:191)
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at com.taobao.eagleeye.EagleEyeFilter.doFilter(EagleEyeFilter.java:81)
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at com.taobao.tomcat.valves.ContextLoadFilterValve.invoke(ContextLoadFilterValve.java:150)
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at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
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at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
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at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
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at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:429)
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at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1085)
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at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
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at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
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- locked org.apache.tomcat.util.net.SocketWrapper@7127ee12
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at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
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at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
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at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
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at java.lang.Thread.run(Thread.java:745)
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Number of locked synchronizers = 1
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- java.util.concurrent.ThreadPoolExecutor$Worker@31a6493e
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```
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::: warning
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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。
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:::
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### thread -i, 指定采样时间间隔
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- `thread -i 1000` : 统计最近 1000ms 内的线程 CPU 时间。
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- `thread -n 3 -i 1000` : 列出 1000ms 内最忙的 3 个线程栈
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```bash
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$ thread -n 3 -i 1000
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"as-command-execute-daemon" Id=4759 cpuUsage=23% RUNNABLE
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at sun.management.ThreadImpl.dumpThreads0(Native Method)
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at sun.management.ThreadImpl.getThreadInfo(ThreadImpl.java:440)
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at com.taobao.arthas.core.command.monitor200.ThreadCommand.processTopBusyThreads(ThreadCommand.java:133)
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at com.taobao.arthas.core.command.monitor200.ThreadCommand.process(ThreadCommand.java:79)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.process(AnnotatedCommandImpl.java:96)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl.access$100(AnnotatedCommandImpl.java:27)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:125)
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at com.taobao.arthas.core.shell.command.impl.AnnotatedCommandImpl$ProcessHandler.handle(AnnotatedCommandImpl.java:122)
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at com.taobao.arthas.core.shell.system.impl.ProcessImpl$CommandProcessTask.run(ProcessImpl.java:332)
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at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
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at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
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at java.lang.Thread.run(Thread.java:756)
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Number of locked synchronizers = 1
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- java.util.concurrent.ThreadPoolExecutor$Worker@546aeec1
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...
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```
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### thread --state ，查看指定状态的线程
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```bash
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[arthas@28114]$ thread --state WAITING
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Threads Total: 16, NEW: 0, RUNNABLE: 9, BLOCKED: 0, WAITING: 3, TIMED_WAITING: 4, TERMINATED: 0
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ID NAME GROUP PRIORITY STATE %CPU DELTA_TIME TIME INTERRUPTE DAEMON
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3 Finalizer system 8 WAITING 0.0 0.000 0:0.000 false true
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20 arthas-UserStat system 9 WAITING 0.0 0.000 0:0.001 false true
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14 arthas-timer system 9 WAITING 0.0 0.000 0:0.000 false true
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```
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