Jim,
if i understand correctly, George point is that OpenMPI is currently
correct with respect to the MPI standard :
MPI_DATATYPE_NULL is *not* a predefined datatype, hence it is not
(expected to be) a committed datatype,
and hence it cannot be used in MPI_Alltoallw (regardless the
correspondi
That's ridiculous. You can have 0 of anything. There is absolutely no
logical reason why MPI_DATATYPE_NULL should not be valid with count=0. Are
you suggesting that one cannot pass buffer=NULL when count=0 either?
Jeff
On Tue, Jan 12, 2016 at 6:06 PM, George Bosilca wrote:
> As JH mentioned
Sorry there was a mistake in that code,
stypes and rtypes should be of type MPI_Datatype not integer
however the result is the same.
*** An error occurred in MPI_Alltoallw
*** reported by process [204406785,1]
*** on communicator MPI_COMM_WORLD
*** MPI_ERR_TYPE: invalid datatype
On Tue, Jan
Maybe the example is too simple. Here is another one which
when run on two tasks sends two integers from each task to
task 0. Task 1 receives nothing. This works with mpich and impi
but fails with openmpi.
#include
#include
my_mpi_test(int rank, int ntasks)
{
MPI_Datatype stype, rtype;
+1
FWIW, the trivial patch below does not make the test run because
MPI_DATATYPE_NULL is not commited.
also, FWIW, this simple test case fails with both OpenMPI and MPICH
(and i expected it to work with MPICH)
/*
* This is a dumb example that sendrecv to/from self
* with MPI_DATATYPE_NULL and
As JH mentioned the examples are not normative. The type MPI_DATATYPE_NULL
is not part of the MPI predefined datatypes, and as such is not expected to
be a commited datatype, thus improper for communications (even when the
count is 0).
George.
On Tue, Jan 12, 2016 at 8:25 PM, Jim Edwards wrot
Hi Gilles,
I think that your conversation with Jeff pretty much covered it but
your understanding of my original problem is correct.
Thanks for the prompt response and the PR.
On Tue, Jan 12, 2016 at 5:59 PM, Jeff Hammond
wrote:
> Consider MPI_Get_accumulate with op=MPI_NO_OP, which is used to
Consider MPI_Get_accumulate with op=MPI_NO_OP, which is used to achieve
atomic Get. Obviously, one does not want to allocate and describe a source
buffer that will not be touched by this. This is a case like MPI_Alltoallw
where (NULL,0,MPI_DATATYPE_NULL) needs to work at participating processes.
Thanks Jeff,
i could not find anything in the standard that says this is an invalid
usage ... so i can only agree this is a bug.
fwiw, example 4.23 is working fine with OpenMPI
but that is a different case : with MPI_Gather and friends, recv stuff
is irrelevant on non root task.
in the case of MP
Example 4.23 of MPI 3.1 (it is hardly a new example, but may have a
different number in older versions) demonstrates the use of
(buffer=NULL,count=0,type=MPI_DATATYPE_NULL). While examples in the MPI
standard are not normative text, this is certainly a valid use of MPI. I
can't find a citation wh
Hi Jim,
can you please confirm my understanding is correct :
- OpenMPI does *not* accept MPI_DATATYPE_NULL as an input of MPI_Alltoallw
- mpich does accept MPI_DATATYPE_NULL as an input of MPI_Alltoallw *if*
the corresponding count *is* zero
- mpich does *not* accept MPI_DATATYPE_NULL as an inp
Hi,
I am using OpenMPI-1.8.3 built with gcc 4.8.3
and I am using an MPI_Alltoallw call to perform
an all to some (or some to all) communication.
In the case in which my task is not sending (or receiving) any data I set
the
datatype for that send or recv buffer to MPI_DATATYPE_NULL - this
works fi
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