Newsgroups: comp.parallel.mpi
From: rwhaley@cupid.cs.utk.edu (R Clint Whaley)
Subject: Re: non-blocking error code
Organization: Computer Science Dept, University of Tennessee, Knoxville
Date: 21 Jun 1995 16:55:03 GMT
Message-ID: <3s9it7INN1vr@CS.UTK.EDU>

In article <3s83iv$hv0@charm.magnus.acs.ohio-state.edu>, rdaoud@magnus.acs.ohio-state.edu (Raja B Daoud) writes:
|> R Clint Whaley <rwhaley@cupid.cs.utk.edu> wrote:
|> >   info = MPI_Isend(buff, length, dest, TAG, comm, &NBID);
|> >   while(info != MPI_SUCCESS)
|> >   {
|> >      MPI_Error_class(info, &errclass);
|> >      if (errclass != OutOfResources) ERROR_EXIT;
|> >      info = MPI_Isend(buff, length, dest, TAG, comm, &NBID); 
|> >   }
|> 
|> How about if MPI_Isend() returns any error, you then call MPI_Send()
|> and block?  If MPI_Send() returns an error then exit.  This way you
|> avoid the busy loop.  There is no error class defined specifically
|> for this case, MPI_ERR_INTERN could be many things other than
|> "no resources (envelopes) left".
|> 
|> --Raja
|> 
|> -=-
|> Raja Daoud				raja@tbag.osc.edu
|> Ohio Supercomputer Center		http://www.osc.edu/lam.html


This is a fine suggestion, but infortunately not one I can use.  I really
need to maintain the non-blocking status, and only block until some of
the previous non-blocking communication has been cleared away.  I am aware
that even if I find the correct error class, I will be accepting many other
kinds of errors.  I still find this better than the alternative: keep trying
on _any_ error.  Therefore, if anyone out there knows with authority what
error class a "out of system resources" report from MPI_Isend would be, it
would be a great help if you would share the info.

I think it would be worth documenting in the MPI standard, since in my
experience, this kind of problem occurs fairly often with extensive use
of non-blocking communication.

Thanks,
Clint
-- 
*****************************************************************
R. Clint Whaley       rwhaley@cs.utk.edu      104 Ayres Hall
HOME: (615) 546-1981  OFFICE: (615) 974-8298  Knoxville TN, 37996
http://www.cs.utk.edu/~rwhaley/Clint.html

