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Subject: Re: [OMPI users] testsome returns negative indices
From: Ross Boylan (ross_at_[hidden])
Date: 2014-03-21 13:17:19

On 3/21/2014 10:02 AM, Jeff Squyres (jsquyres) wrote:
> So just to be clear, the C interface for MPI_Testsome is:
> int MPI_Testsome(int incount, MPI_Request requests[],
> int *outcount, int indices[],
> MPI_Status statuses[]);
> And your R call is:
> mpi_errhandler(MPI_Testsome(countn, request, &INTEGER(indices)[0],
> &INTEGER(indices)[1], status));
> I'm assuming request is an MPI_Request object.
It's a pointer to an array of such objects.
static MPI_Request *request;
request=(MPI_Request *)Calloc(REQUEST_MAXSIZE, MPI_Request);
> And integer(indices)[0] is where you want the outcount to go, and then integer(indices)[1] through [value_of_outcount] is where you want the indices to go, right?
> If so, then yes, that looks proper.
> You'll probably need to look into what's happening in the R wrapper as to why you're not getting the right answers, sorry.
> (and yes, the values in the indices[] array should be between 0 and (incount-1))
I'm getting increasingly suspicious that this could be an integer size
mismatch, maybe from different compilation options. I think R uses 32
bits (even on 64 bit machines) and MPI uses 64, even though both have
type int. R defines
#define INTEGER(x) ((int *) DATAPTR(x))

What should the integer size be for MPI on 64 bit architectures,
specifically linux gcc (Debian 4.4.5-8) 4.4.5?

> On Mar 21, 2014, at 12:01 PM, Ross Boylan <ross_at_[hidden]> wrote:
>> On Fri, 2014-03-21 at 14:11 +0000, Jeff Squyres (jsquyres) wrote:
>>> Is that C or R code?
>> C.
>>> If it's R, I think the next step would be to check the R wrapper for MPI_Testsome and see what is actually being returned by OMPI in C before it gets converted to R. I'm afraid I don't know R, so I can't really comment on the syntax / correctness of your code snipit.
>>> If it's C -- which I don't think it is, but it *could* be...? -- I would need to understand your syntax in calling MPI_Testsome better; e.g., what's &INTEGER(foo)[x]?
>> allocVector(INTSXP, countn+1) allocates an R vector of integers.
>> INTEGER(indices) returns the data portion of that structure, where the
>> actual integers go. The &...[0] get the address of the first location.
>> PROTECT keeps things from being garbage-collected by R.
>> The allocation of indices is a cheat: the first location is used for the
>> outcount, and the following locations get the actual indices.
>> status is a pointer to an array of MPI status objects,
>> The indices should be small integers, shouldn't they? I'm also getting
>> some large values back.
>> Ross
>>> On Mar 20, 2014, at 8:39 PM, Ross Boylan <ross_at_[hidden]> wrote:
>>>> MPI_Testsome seems to have returned successfully, with a positive outcount, and yet given me a negative index, -4432. Can anyone help me understand what's going on?
>>>> The call is from R, and so there might be a translation issue. My first thought was that it might be 32 vs 64 bit integers, but both OMPI and R seem to be using the C int type for the integers.
>>>> Here's the inner call:
>>>> SEXP mpi_testsome(SEXP sexp_count){
>>>> int countn=INTEGER(sexp_count)[0];
>>>> SEXP indices;
>>>> PROTECT (indices = allocVector(INTSXP, countn+1));
>>>> mpi_errhandler(MPI_Testsome(countn, request, &INTEGER(indices)[0],
>>>> &INTEGER(indices)[1], status));
>>>> UNPROTECT(1);
>>>> return indices;
>>>> }
>>>> SEXP is an R structure.
>>>> OMPI 1.7.4.
>>>> Ross Boylan
>>>> _______________________________________________
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