[MPICH] Collective write when only a subset of processes have data to write

[Heshan Lin]

Thanks for your response, Rob. But I am not sure how to set parameters for
MPI_File_set_view and MPI_File_wirte_all for processes with no data to
write. I tried writing 0 length of data but got errors. By any chance you
can point me to some examples? 

Heshan

> -----Original Message-----
> From: Robert Latham [mailto:robl at mcs.anl.gov]
> Sent: Monday, February 05, 2007 10:53 AM
> To: Heshan Lin
> Cc: mpich-discuss at mcs.anl.gov
> Subject: Re: [MPICH] Collective write when only a subset of processes have
data
> to write
> 
> On Sun, Feb 04, 2007 at 07:59:56PM -0500, Heshan Lin wrote:
> > Hi,
> >
> > I am testing collective write with a parallel program in which every MPI
> > process needs to periodically output non-contiguous data. The basic
program
> > structure for each MPI process looks like following.
> >
> > MPI_File_open(MPI_COMM_WORLD)
> > WHILE (not end) {
> >     Computation()
> >     MPI_File_set_view()
> >     MPI_File_write_all()
> > }
> >
> > One problem I have encountered now is that at some iteration there are
only
> > a subset of MPI processes having data to write. In that case the program
> > will hang if not all processes issue write requests.
> 
> Go ahead and have all processes --  even those with no work to do --
> call MPI_File_write_all.  The MPI-IO implementation will know what do
> to.
> 
> ==rob
> 
> --
> Rob Latham
> Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
> Argonne National Lab, IL USA                 B29D F333 664A 4280 315B