[yt-users] curious warning message in parallelHOP

[Britton Smith]

I made the change.  It was PR #35.  People were on board with it back when
it was accepted, but if it's forking, then I agree we should just get rid
of it.  After that was put it, another issue crept up as it was found that
the command that it calls doesn't even always return the same format on
every system.  I guess that's the risk you run when making system calls.  I
support killing it.

Britton

On Wed, May 9, 2012 at 8:37 PM, John Wise <jwise at physics.gatech.edu> wrote:

> Hi Matt and Geoffrey,
>
> If you're talking to this John, I didn't make that change.  I think
> Britton made that change in changeset ab0e7664f75d.
>
> But if popen() creates forks, I'd -1 on this being default, also because
> it causes problems in some MPI implementations, as Geoffrey has found out
> the hard way!
>
> John
>
>
> On 05/09/2012 08:23 PM, Matthew Turk wrote:
>
>> Hi Geoffrey,
>>
>> Grepping through the yt codebase, I think the most likely culprit is
>> that get_memory_usage (which I believe gets called often during
>> parallel HOP) falls back on calling popen, which results in a fork.  I
>> think John might have added this.  I am -1 on this being default
>> behavior, and +1 on changing fallback (by default) to just return 0 if
>> it can't get memory information from the resource module, and maybe
>> governing this with a config parameter.  John, what do you think?
>>
>> -MAtt
>>
>> On Wed, May 9, 2012 at 7:46 PM, Geoffrey So<gsiisg at gmail.com>  wrote:
>>
>>> I got this warning message when running paralllel HOP, which I guess was
>>> there before but never noticed before because it's close to the top
>>> (usually
>>> looking at the bottom of the logs).  I was wondering if there's anything
>>> I
>>> need to worry about?
>>>
>>> ------------------------------**------------------------------**
>>> --------------
>>> An MPI process has executed an operation involving a call to the
>>> "fork()" system call to create a child process.  Open MPI is currently
>>> operating in a condition that could result in memory corruption or
>>> other system errors; your MPI job may hang, crash, or produce silent
>>> data corruption.  The use of fork() (or system() or other calls that
>>> create child processes) is strongly discouraged.
>>>
>>> The process that invoked fork was:
>>>
>>>   Local host:          lens51 (PID 6818)
>>>   MPI_COMM_WORLD rank: 323
>>>
>>> If you are *absolutely sure* that your application will successfully
>>> and correctly survive a call to fork(), you may disable this warning
>>> by setting the mpi_warn_on_fork MCA parameter to 0.
>>> ------------------------------**------------------------------**
>>> --------------
>>> [lens6:19012] 447 more processes have sent help message
>>> help-mpi-runtime.txt
>>> / mpi_init:warn-fork
>>> [lens6:19012] Set MCA parameter "orte_base_help_aggregate" to 0 to see
>>> all
>>> help / error messages
>>> [lens6:19012] 32 more processes have sent help message
>>> help-mpi-runtime.txt
>>> / mpi_init:warn-fork
>>> [lens6:19012] 32 more processes have sent help message
>>> help-mpi-runtime.txt
>>> / mpi_init:warn-fork
>>>
>>> From
>>> G.S.
>>>
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>
> --
> John Wise
> Assistant Professor of Physics
> Center for Relativistic Astrophysics, Georgia Tech
>
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