Table of Contents

Arthas Async Jobs

Async Jobs online tutorial

Asynchronous jobs in arthas. The idea is borrowed from linux jobs.

1. Use & to run the command in the background

For example, execute the trace command in the background:

trace Test t &

By doing this, the current command is put to the background to run, you can continue to execute other commands in the console.

2. List background jobs

If you want to list all background jobs, you can execute the jobs command and the results are as follows:

$ jobs
[10]*
       Stopped           watch com.taobao.container.Test test "params[0].{? #this.name == null }" -x 2
       execution count : 19
       start time      : Fri Sep 22 09:59:55 CST 2017
       timeout date    : Sat Sep 23 09:59:55 CST 2017
       session         : 3648e874-5e69-473f-9eed-7f89660b079b (current)

You can see that there is currently a background job executing:

• job id is 10, * indicates that this job is created by the current session.
• status is Stopped
• execution count is the number of executions, which have been executed 19 times since the start.
• timeout date: timeout timestamp, when the time exceeds this timestamp, the job will be automatically timeout and exit.

3. Suspend and cancel job

When the job is executing in the foreground, for example, directly executing the command trace Test t, or executing the background job command trace Test t &, then putting the job back to the foreground via fg command, the console cannot continue to execute other command, but can receive and process the following keyboard events:

• ‘ctrl + z’: Suspends the job, the job status will change to Stopped, and the job can be restarted by bg <job-id> or fg <job-id>
• ‘ctrl + c’: Stops the job
• ‘ctrl + d’: According to linux semantics this should lead to exit the terminal, right now Arthas has not implemented this yet, therefore simply ignore this keystroke.

4. fg/bg, switch the job from the foreground to the background, and vise verse

• When a job is executed in the background or in suspended status (use ctrl + z to suspend job), fg <job-id> can transfer the job to the foreground to continue to run.
• When a job is in suspended status (use ctrl + z to suspend job), bg <job-id> can put the job to the background to continue to run.
• A job created by other session can only be put to the foreground to run by using fg in the current session.

5. Redirect the output

The job output can be redirect to the specified file by > or >>, and can be used together with &. By doing this, you can achieve running commands asynchronously, for example:

$ trace Test t >> test.out &

At this time, the trace command will be executed in the background, and the result will be output to the test.out file under the working directory of the application. You can continue to execute other commands. And you can view the command execution result in the file. You can execute the pwd command to view the working directory of the current application.

$ cat test.out

If no redirect file is specified, the result will be output to the ~/logs/arthas-cache/ directory, for example:

$ trace Test t >> &
job id : 2
cache location : /Users/admin/logs/arthas-cache/28198/2

At this time, the command will be executed asynchronously in the background, and the result will be asynchronously saved in the file (~/logs/arthas-cache/${PID}/${JobId});

• At this time, the execution of the task is not affected by the session disconnection; the default timeout period of the task is 1 day, and the default timeout period can be modified through the global options command;
• The result of this command will be output asynchronously to the file; at this time, regardless of whether save-result is true or not, the result will not be written asynchronously to ~/logs/arthas-cache/result.log.

6. Stop job

If you want to stop background job, just kill <job-id>.

7. Others

• Support up to 8 commands at the same time to redirect the output to the log files.
• Do not open too many background jobs at the same time to avoid negative performance effect to the target JVM.
• If you do not want to stop the Arthas service and continue to perform background tasks, you can exit the Arthas console by executing quit command (stop command will stop the Arthas service)