Who wrote Example 4.23 of MPI 3.1? I propose to add the exception rather than delete that example. I do not want to have to use real datatypes when sending nothing. Is NULL a valid buffer handle? Can I pass null pointers when count=0? Jeff On Tuesday, January 12, 2016, William Gropp <[email protected]> wrote:

The standard says that the null handles are invalid for input unless explicitly permitted. There’s no exemption for a datatype argument where the associated count is zero.

Bill

William Gropp Director, Parallel Computing Institute Thomas M. Siebel Chair in Computer Science Chief Scientist, NCSA University of Illinois Urbana-Champaign

On Jan 12, 2016, at 9:26 PM, Jeff Hammond <[email protected] <javascript:_e(%7B%7D,'cvml','[email protected]');>> wrote:

Is it allowed to communicate messages with (buffer=NULL,count=0,type=MPI_DATATYPE_NULL)?

George thinks MPI_DATATYPE_NULL cannot be used even when count=0, which I think is ridiculous, particularly when one makes the analogy to buffer=NULL.

See http://www.open-mpi.org/community/lists/users/2016/01/28255.php <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.open-2Dmpi.org_community_lists_users_2016_01_28255.php&d=BQMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=195OD1c98cxYlIPBUDzl00KueizThEKs34a9DvL37eY&m=tWmZZT774xAE-RjUpTuHeZ0-hHkwEoE5sQADPmobarg&s=7rkfIDjMiCphV1WD00EIRKeH44dIa97JAz6C3HTPF7M&e=> for the thread in question.

There is example code in MPI that uses this behavior. George and I agree that example text is non-normative, but I cannot imagine how this example came to exist without the Forum believing it to be valid.

Jeff

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