thread
======

> Check the basic info and stack trace of the target thread.

### Parameters

|Name|Specification|
|---:|:---|
|*id*|thread id in JVM|
|`[n:]`|the top n busiest threads with stack traces printed|
|`[b]`|locate the thread blocking the others|
|[i `<value>`]|specify the interval to collect data to compute CPU ratios (ms)|

> How the CPU ratios are calculated? <br/><br/>
> CPU ratio for a given thread is the CPU time it takes divided by the total CPU time within a specified interval period. It is calculated in the following way: sample CPU times for all the thread by calling `java.lang.management.ThreadMXBean#getThreadCpuTime` first, then sleep for a period (the default value is 100ms, which can be specified by `-i`), then sample CPU times again. By this, we can get the time cost for this period for each thread, then come up with the ratio. <br/><br/>
> Note: this operation consumes CPU time too (`getThreadCpuTime` is time-consuming), therefore it is possible to observe Arthas's thread appears in the list. To avoid this, try to increase sample interval, for example: 5000 ms.<br/><br/>
> If you'd like to check the CPU ratios from the very beginning of the Java process, [show-busy-java-threads](https://github.com/oldratlee/useful-scripts/blob/master/docs/java.md#-show-busy-java-threads) can come to help. 

### Usage

#### List the top n busiest threads with detailed stack trace

```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)
```

#### List all threads' info when no options provided

```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, show the running stack for the target thread

```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, locate the thread bocking the others

In some occasions, we experience the whole application is stuck because there's one particular thread hold one lock that other threads are relying on. To diagnose such an issue, Arthas provides `thread -b` to find the problematic thread in one single command.

```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
```

> Note: By now Arthas only supports to locate the thread blocked by `synchronzied`, while `java.util.concurrent.Lock` is not supported yet.


#### thread -i, specify the sampling interval

```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
...
```