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
...
```
