[petsc-users] ASCIIRead error for multiple processors

[Matthew Knepley]

On Fri, Apr 5, 2019 at 10:27 AM Yuyun Yang <yyang85 at stanford.edu> wrote:

> Hmm ok. Then should I use this function or not when I'm reading the input?
> It's probably still going to give me the same error and unable to proceed?
>
> I'd like to know if I should use something else to work around this
> problem.
>

No, what you do is

  if (!rank) {
    PetscViewerASCIIRead();
    MPI_Bcast();
  } else {
    MPI_Bcast();
  }

  Thanks,

     Matt


> Thanks,
> Yuyun
>
> Get Outlook for iOS <https://aka.ms/o0ukef>
> ------------------------------
> *From:* Matthew Knepley <knepley at gmail.com>
> *Sent:* Friday, April 5, 2019 5:16:12 AM
> *To:* Yuyun Yang
> *Cc:* Smith, Barry F.; petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] ASCIIRead error for multiple processors
>
> On Thu, Apr 4, 2019 at 10:56 PM Yuyun Yang <yyang85 at stanford.edu> wrote:
>
>> So do I call MPI_Bcast right after I call PetscViewerASCIIRead? Is that
>> going to prevent the other processors from trying to read the same file but
>> were unable to?
>>
>
> No, all this does is replicate data from process 0 on the other processes.
>
>    Matt
>
>
>> Thanks,
>> Yuyun
>>
>> Get Outlook for iOS <https://aka.ms/o0ukef>
>> ------------------------------
>> *From:* Matthew Knepley <knepley at gmail.com>
>> *Sent:* Thursday, April 4, 2019 7:30:20 PM
>> *To:* Yuyun Yang
>> *Cc:* Smith, Barry F.; petsc-users at mcs.anl.gov
>> *Subject:* Re: [petsc-users] ASCIIRead error for multiple processors
>>
>> On Thu, Apr 4, 2019 at 9:19 PM Yuyun Yang via petsc-users <
>> petsc-users at mcs.anl.gov> wrote:
>>
>>> We are probably not going to use hundreds of processors, but i think it
>>> would be good to just have processor 0 read the input and broadcast that to
>>> all the other processors. Would that be a possible fix? And what would you
>>> suggest to work around this problem for now?
>>>
>>
>> Explicitly call MPI_Bcast().
>>
>>    Matt
>>
>>
>>> Thanks!
>>> Yuyun
>>>
>>> Get Outlook for iOS <https://aka.ms/o0ukef>
>>> ------------------------------
>>> *From:* Smith, Barry F. <bsmith at mcs.anl.gov>
>>> *Sent:* Thursday, April 4, 2019 3:07:37 PM
>>> *To:* Yuyun Yang
>>> *Cc:* petsc-users at mcs.anl.gov
>>> *Subject:* Re: [petsc-users] ASCIIRead error for multiple processors
>>>
>>>
>>>    Currently PetscViewerFileSetName_ASCII() only opens the file on
>>> process 0 (for read or write) thus when you call PetscViewerASCIIRead()
>>> from any process but the first it will be reading from an fd that has not
>>> been set and you could get unpredictable results.
>>>
>>>    The implementation and documentation for PetscViewerASCIIRead() is
>>> buggy.
>>>
>>>    There are two possible fixes we could make
>>>
>>> 1) have PetscViewerFileSetName_ASCII()  open the file for reading on all
>>> processes or
>>> 2) have PetscViewerASCIIRead() generate an error if the process is not
>>> rank == 0
>>>
>>>    Barry
>>>
>>> Note that using PetscViewerASCIIRead() from a handful of processes is
>>> probably fine but having hundreds or thousands of processes open the same
>>> ASCII file and reading from it will likely not be scalable.
>>>
>>>
>>>
>>>
>>> > On Apr 4, 2019, at 3:15 PM, Yuyun Yang via petsc-users <
>>> petsc-users at mcs.anl.gov> wrote:
>>> >
>>> > Hello team,
>>> >
>>> > I’m trying to use PetscViewerASCIIRead() to read in a single
>>> interger/scalar value from an input file. It works for one processor.
>>> However, when running on multiple processors, I’m getting the below error:
>>> >
>>> > [1]PETSC ERROR: Invalid argument
>>> > [1]PETSC ERROR: Insufficient data, read only 0 < 1 items
>>> > [1]PETSC ERROR: #1 PetscViewerASCIIRead() line 1054 in
>>> /usr/local/CLAB-2/petsc-3.6/src/sys/classes/viewer/impls/ascii/filev.c
>>> >
>>> > Is there something wrong with how I’m implementing this, or ASCIIRead
>>> does not work with multiple processors?
>>> >
>>> > Thanks,
>>> > Yuyun
>>>
>>>
>>
>> --
>> What most experimenters take for granted before they begin their
>> experiments is infinitely more interesting than any results to which their
>> experiments lead.
>> -- Norbert Wiener
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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