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Arthas Async Jobs
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===
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Asynchronous jobs in arthas, using commands related to linux jobs.[linux man jobs](http://man7.org/linux/man-pages/man1/jobs.1p.html)。
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## 1. Use & to run the command in the background
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For example, execute the trace command in the background:
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```bash
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trace Test t &
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```
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## 2. List background jobs
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If you want to list all background jobs, you can execute the `jobs` command and the results are as follows:
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```bash
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$ jobs
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[10]*
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Stopped watch com.taobao.container.Test test "params[0].{? #this.name == null }" -x 2
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execution count : 19
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start time : Fri Sep 22 09:59:55 CST 2017
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timeout date : Sat Sep 23 09:59:55 CST 2017
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session : 3648e874-5e69-473f-9eed-7f89660b079b (current)
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```
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You can see that there is currently a background job executing.
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* job id is 10, `*` indicates that this job is created by the current session.
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* status is `Stopped`
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* execution count is the number of executions, which have been executed 19 times since the start.
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* timeout date: After this time, the job will automatically timeout and exit.
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## 3. Suspend and Cannel job
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When the job is executing in the foreground, such as directly calling the command `trace Test t` or calling the background job command `trace Test t &`, the job is transferred to the foreground through the `fg` command. At this point, the console cannot continue to execute the command, but can receive and process the following keyboard events:
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* ‘ctrl + z’: Suspend the job, the job status will change to `Stopped`, and the job can be restarted by `bg <job-id>` or `fg <job-id>`
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* ‘ctrl + c’: Stop the job
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* ‘ctrl + d’: According to linux semantics should be the exit terminal, currently arthas ignore this input.
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## 4. fg/bg, Bring a background job to the foreground/Restart a stopped background job
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* When the job is executed in the background or suspended (`ctrl + z` to suspend job), executing `fg <job-id>` will transfer the corresponding job to the foreground to continue execution.
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* When the job is suspended (`ctrl + z` to suspend job), executing `bg <job-id>` will continue the corresponding job in the background.
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* A job created by a non-current session can only be executed by the current session fg to the foreground.
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## 5. Redirect the job output
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The job output can be redirect to the specified file by `>` or `>>`, and can be used together with `&` to implement the asynchronous job of the arthas command. such as:
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```bash
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$ trace Test t >> test.out &
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```
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The trace command will be executed in the background and the output will be redirect to `~/logs/arthas-cache/test.out`. You can continue to execute other commands in the console.
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When connecting to a remote arthas server, you may not be able to view the files of the remote machine. Arthas also supports automatic redirection to the local cache file. Examples are as follows:
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```bash
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$ trace Test t >> &
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job id : 2
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cache location : /Users/gehui/logs/arthas-cache/28198/2
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```
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You can see that does not specify the redirect file after `>>`, arthas will automatically redirect the job output to the `~/logs/arthas-cache`.
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In the above example, pid is `28198` and job id is `2`.
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## 6. Stop job
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If you want to stop background job, just `kill <job-id>`.
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## 7. Others
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* Support up to 8 commands at the same time redirect the output to the log file.
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* Do not open too many background asynchronous commands at the same time to avoid affecting the performance of the target JVM. |