[jira] [Comment Edited] (YARN-9667) Container-executor.c duplicates messages to stdout

["Peter Bacsko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-9667?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16880230#comment-16880230 ] 

Peter Bacsko edited comment on YARN-9667 at 7/8/19 11:35 AM:
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I suggest considering two things:

1) When setting {{ERRORFILE}} and {{LOGFILE}}, just invoke {{setbuf(ERRORFILE, NULL);}} and {{setbuf(LOGFILE, NULL);}}. Then writing the output will be written to the stream immediately without buffering.

2) We should use {{_exit()}} in the child process. After doing some research, this is the preferred method of exiting from a child process. There are some exceptions, but in general this seems to be the commonly used way of terminating a child. Eg. if {{execvp()}} fails then just bail out, avoid any sort of cleanup. This avoids flusing buffers twice, plus avoids calling functions registered with {{atexit()}} twice, which probably we don't have right now, but guarding against a potential bug is always a good thing.


was (Author: pbacsko):
I suggest considering two things:

1) When setting ERRORFILE or LOGFILE, just invoke {{setbuf(ERRORFILE, NULL);}} and {{setbuf(LOGFILE, NULL);}}. Then writing the output will be written to the stream immediately without buffering.

2) We should use {{_exit()}} in the child process. After doing some research, this is the preferred method of exiting from a child process. There are some exceptions, but in general this seems to be the commonly used way of terminating a child. Eg. if {{execvp()}} fails then just bail out, avoid any sort of cleanup. This avoids flusing buffers twice, plus avoids calling functions registered with {{atexit()}} twice, which probably we don't have right now, but guarding against a potential bug is always a good thing.

> Container-executor.c duplicates messages to stdout
> --------------------------------------------------
>
>                 Key: YARN-9667
>                 URL: https://issues.apache.org/jira/browse/YARN-9667
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: nodemanager, yarn
>    Affects Versions: 3.2.0
>            Reporter: Adam Antal
>            Priority: Major
>
> When a container is killed by its AM we get a similar error message like this:
> {noformat}
> 2019-06-30 12:09:04,412 WARN org.apache.hadoop.yarn.server.nodemanager.containermanager.linux.privileged.PrivilegedOperationExecutor: Shell execution returned exit code: 143. Privileged Execution Operation Stderr:
> Stdout: main : command provided 1
> main : run as user is systest
> main : requested yarn user is systest
> Getting exit code file...
> Creating script paths...
> Writing pid file...
> Writing to tmp file /yarn/nm/nmPrivate/application_1561921629886_0001/container_e84_1561921629886_0001_01_000019/container_e84_1561921629886_0001_01_000019.pid.tmp
> Writing to cgroup task files...
> Creating local dirs...
> Launching container...
> Getting exit code file...
> Creating script paths...
> {noformat}
> In container-executor.c the fork point is right after the "Creating script paths..." part, though in the Stdout log we can clearly see it has been written there twice. After consulting with [~pbacsko] it seems like there's a missing flush in container-executor.c before the fork and that causes the duplication.
> I suggest to add a flush there so that it won't be duplicated: it's a bit misleading that the child process writes out "Getting exit code file" and "Creating script paths" even though it is clearly not doing that.
> A more appealing solution could be to revisit the fprintf-fflush pairs in the code and change them to a single call, so that the fflush calls would not be forgotten accidentally. (It can cause problems in every place where it's used).
> Note: this issue probably affects every occasion of fork(), not just the one from {{launch_container_as_user}} in {{main.c}}.



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