As a general idea and following similar MPI concepts, it can be really useful if MPI_BUFFER_ATTACH/DETACH allowed a layered usage, inside modules. That is, inside a call, a library can make a 'detach' and cache it, next 'attach' an internally allocated resource, call BSEND, 'detach' it own resources, and finaly re-'attach' the original resources. I've already disccussed this a bit with Bill Gropp, regarding MPICH2 behaviour.
So I would to propose the following: 1- MPI_BUFFER_ATTACH should attach the provided buffer, raising an error if the provided size is less than BSEND_OVERHEAD (why to postpone the error until MPI_Bsend?). Currently, the behavior is: In [1]: from mpi4py import MPI In [2]: mem = MPI.Alloc_mem(1) In [3]: mem Out[3]: <read-write buffer ptr 0x8c561c8, size 1 at 0xf6c38040> In [4]: MPI.Attach_buffer(mem) In [5]: MPI.BSEND_OVERHEAD Out[5]: 128 Any subsequent MPI_BSEND is likely to fail for lack of buffer space. Am I right? 2- MPI_BUFFER_ATTACH should raise an error if a previous buffer was attached. OMPI currently seems to work like this, however in a second call to attach i get an error code -104, which I think is internal and should be remaped to public range [SUCCESS, LASTCODE). See below, the error string is generated by MY code, because I asumed as a genral rule that calling MPI_GET_ERROR_STRING is unsafe with an out of range error code. In [6]: MPI.Attach_buffer(mem) --------------------------------------------------------------------------- mpi4py.MPI.Exception Traceback (most recent call last) # more output .... Exception: unable to retrieve error string, ierr=-104 out of range [MPI_SUCCESS=0, MPI_ERR_LASTCODE=54) 3 - MPI_BUFFER_DETACH should always success, even if there is no buffer to detach. In the last case, it should return a null pointer, and perhaps a zero size. This way, inside a library routine we can safely call MPI_BUFFER_DETACH, MPI_BUFFER_ATTACH/DETACH owned memory, and finally test if original buffer (gotten in the initial call to detach) is valid buy testing pointer or size. Waiting for your comments... Regards, -- Lisandro Dalcín --------------- 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
