[petsc-users] ASCIIRead error for multiple processors

[Yuyun Yang]

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?

Thanks,
Yuyun

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________________________________
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<mailto: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

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________________________________
From: Smith, Barry F. <bsmith at mcs.anl.gov<mailto:bsmith at mcs.anl.gov>>
Sent: Thursday, April 4, 2019 3:07:37 PM
To: Yuyun Yang
Cc: petsc-users at mcs.anl.gov<mailto: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<mailto: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



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