add en async.md. #51

site/src/site/sphinx/async.md

@@ -36,8 +36,8 @@ $ jobs
 * ‘ctrl + d’：按照linux语义应当是退出终端，目前arthas中是空实现，不处理
 
 ## 4. fg、bg命令，将命令转到前台、后台继续执行
-* 任务在后台执行或者暂停状态（‘ctrl + z’暂停任务）时，执行fg <job-id>将可以把对应的任务转到前台继续执行。在前台执行时，无法在console中执行其他命令
-* 当任务处于暂停状态时（‘ctrl + z’暂停任务），执行bg <job-id>将可以把对应的任务在后台继续执行
+* 任务在后台执行或者暂停状态（`ctrl + z`暂停任务）时，执行`fg <job-id>`将可以把对应的任务转到前台继续执行。在前台执行时，无法在console中执行其他命令
+* 当任务处于暂停状态时（`ctrl + z`暂停任务），执行`bg <job-id>`将可以把对应的任务在后台继续执行
 * 非当前session创建的job，只能由当前session fg到前台执行
 
 ## 5. 任务输出重定向
@@ -48,7 +48,7 @@ $ trace Test t >> test.out &
 ```
 这时trace命令会在后台执行，并且把结果输出到~/logs/arthas-cache/test.out。可继续执行其他命令。并可查看文件中的命令执行结果。
 
-当远程调用时，可能无法确定机器文件路径，arthas同时支持了自动重定向到缓存路径。使用方法如下：
+当连接到远程的arthas server时，可能无法查看远程机器的文件，arthas同时支持了自动重定向到本地缓存路径。使用方法如下：
 ```sh
 $ trace Test t >>  &
 job id  : 2

site/src/site/sphinx/en/async.md

@@ -0,0 +1,83 @@
+Arthas Async Jobs
+===
+
+Asynchronous jobs in arthas, using commands related to linux jobs.[linux man jobs](http://man7.org/linux/man-pages/man1/jobs.1p.html)。
+
+
+## 1. Use & to run the command in the background
+
+For example, execute the trace command in the background:
+
+```sh
+trace Test t &  
+```
+
+## 2. List background jobs
+
+If you want to list all background jobs, you can execute the `jobs` command and the results are as follows:
+
+
+```sh
+$ 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: After this time, the job will automatically timeout and exit.
+
+## 3. Suspend and Cannel job
+
+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:
+
+* ‘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>`
+* ‘ctrl + c’: Stop the job
+* ‘ctrl + d’: According to linux semantics should be the exit terminal, currently arthas ignore this input.
+
+
+
+## 4. fg/bg, Bring a background job to the foreground/Restart a stopped background job
+
+* 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. 
+* When the job is suspended (`ctrl + z` to suspend job), executing `bg <job-id>` will continue the corresponding job in the background.
+* A job created by a non-current session can only be executed by the current session fg to the foreground.
+
+## 5. Redirect the job output
+
+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:
+
+```sh
+$ trace Test t >> test.out &
+```
+
+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.
+
+
+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:
+
+```sh
+$ trace Test t >>  &
+job id  : 2
+cache location  : /Users/gehui/logs/arthas-cache/28198/2
+```
+
+You can see that does not specify the redirect file after `>>`, arthas will automatically redirect the job output to the `~/logs/arthas-cache`.
+
+In the above example, pid is `28198` and job id is `2`.
+
+## 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 redirect the output to the log file.
+* Do not open too many background asynchronous commands at the same time to avoid affecting the performance of the target JVM.