Re: branch master updated: doc: Recommend avoiding execl, execle or execlp in mcron job specifications.

Re: branch master updated: doc: Recommend avoiding execl, execle or execlp in mcron job specifications.

[Ludovic Courtès]

Hello,

guix-commits@gnu.org skribis:

> diff --git a/doc/guix.texi b/doc/guix.texi
> index e547d469f4..caa6976a82 100644
> --- a/doc/guix.texi
> +++ b/doc/guix.texi
> @@ -18940,9 +18940,8 @@ gexps to introduce job definitions that are passed to mcron
>    ;; job's action as a Scheme procedure.
>    #~(job '(next-hour '(3))
>           (lambda ()
> -           (execl (string-append #$findutils "/bin/updatedb")
> -                  "updatedb"
> -                  "--prunepaths=/tmp /var/tmp /gnu/store"))
> +           (system* (string-append #$findutils "/bin/updatedb")
> +                    "--prunepaths=/tmp /var/tmp /gnu/store"))
>           "updatedb"))
>  
>  (define garbage-collector-job
> @@ -18980,6 +18979,12 @@ the job would appear as ``Lambda function'' in the output of
>  @command{herd schedule mcron}, which is not nearly descriptive enough!
>  @end quotation
>  
> +@quotation Tip
> +Avoid calling the Guile procedures @code{execl}, @code{execle} or
> +@code{execlp} inside a job specification, else mcron won't be able to
> +output the completion status of the job.
> +@end quotation

The problem is that this creates an additional process and the first one
now just sits there in ‘waitpid’.

Could mcron return the completion status of the process that calls the
thunk?  It suppose it’s already monitoring it (via SIGCHLD or a direct
‘waitpid’ call) so it should have that info available, no?

I hope this makes sense.

Ludo’.

Re: branch master updated: doc: Recommend avoiding execl, execle or execlp in mcron job specifications.

[Maxim Cournoyer]

Hi Ludovic,

Ludovic Courtès <ludo@gnu.org> writes:

> Hello,
>
> guix-commits@gnu.org skribis:
>
>> diff --git a/doc/guix.texi b/doc/guix.texi
>> index e547d469f4..caa6976a82 100644
>> --- a/doc/guix.texi
>> +++ b/doc/guix.texi
>> @@ -18940,9 +18940,8 @@ gexps to introduce job definitions that are passed to mcron
>>    ;; job's action as a Scheme procedure.
>>    #~(job '(next-hour '(3))
>>           (lambda ()
>> -           (execl (string-append #$findutils "/bin/updatedb")
>> -                  "updatedb"
>> -                  "--prunepaths=/tmp /var/tmp /gnu/store"))
>> +           (system* (string-append #$findutils "/bin/updatedb")
>> +                    "--prunepaths=/tmp /var/tmp /gnu/store"))
>>           "updatedb"))
>>  
>>  (define garbage-collector-job
>> @@ -18980,6 +18979,12 @@ the job would appear as ``Lambda function'' in the output of
>>  @command{herd schedule mcron}, which is not nearly descriptive enough!
>>  @end quotation
>>  
>> +@quotation Tip
>> +Avoid calling the Guile procedures @code{execl}, @code{execle} or
>> +@code{execlp} inside a job specification, else mcron won't be able to
>> +output the completion status of the job.
>> +@end quotation
>
> The problem is that this creates an additional process and the first one
> now just sits there in ‘waitpid’.
>
> Could mcron return the completion status of the process that calls the
> thunk?  It suppose it’s already monitoring it (via SIGCHLD or a direct
> ‘waitpid’ call) so it should have that info available, no?

Yes, that should be possible, and I agree that's desirable.  We'd have
to move the finalization logging from 'run-job' to 'child-cleanup', both
defined in (mcron base), moving or factoring out 'seconds-since' and
also recording the start date of the job in the <job-data> record
returned by 'run-job'.

My personal mcron TODO now reads:

--8<---------------cut here---------------start------------->8---
* mcron
** TODO Add a 'test' command to run scheduled action *now*
** TODO Log job completion status upon SIGCHLD
--8<---------------cut here---------------end--------------->8---

But feel free to beat me to it!

-- 
Thanks,
Maxim