On 11 February 2010 15:06, George Bosilca <bosi...@eecs.utk.edu> wrote: > This is absolutely not true. Open MPI supports zero length collective > operations (all of them actually), but if their arguments are correctly > shaped. >
OK, you are right here ... > What you're asking for is a free ticket to write MPI calls that do not follow > the MPI requirements when a special value for count is given. > But you did not answer my previous question... What's the rationale for requiring sendbuf!=recvbuf when count=0? I would argue you want a free ticket :-) to put restrictions on user code (without an actual rationale) in order to simplify your implementation. > While zero-length arrays/sequence/containers do appears in real code, they > are not equal to NULL. If they are NULL, that means they do not contain any > useful data, and they don't need to be source or target of any kind of > [collective or point-to-point] communications. > Yes, I know. Moreover, I agree with you. NULL should be reserved for invalid pointers, not for zero-length array... The problem is that people out there seem to disagree or just do not pay any attention to this, thus (pointer=NULL,length=0) DO APPEAR in real life (like the Python example I previously showed you)... Additionally, some time ago (while discussing MPI_Alloc_mem(size=0)) we commented on the different return values for malloc(0) depending on the platform... Well, this discussion got too far... In the end, I agree that representing zero-length arrays with (pointer=NULL,length=0) should be regarded as bad practice... -- Lisandro Dalcin --------------- Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC - Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54-(0)342-451.1594
