On Thu, 2008-05-15 at 17:44 -0400, Richard Treumann wrote:

The MPI_NO_SEND_CANCEL is only useful for cases where libmpi must devote extra memory, longer code paths or extra space in message headers across an entire run just to have the information it needs to do MPI_CANCEL correctly is somebody happens to call it. If a particular MPI implementation does not incur extra costs to be ready for a potential MPI_CANCEL then the implementation will ignore this assertion.

To me I see little benefit in offering MPI_NO_SEND_CANCEL as a hint, all that does is say to the library that a cancel is unlikely to happen and we all know that anyway. As a cancel is still possible I see no opportunity for optimisation of any kind making itself possible, all the extra space in headers and longer code paths would still be needed anyway. As an assertion it would offer some scope for library writers to make simplifications leading to better performance, as a hint I can't see how it would change anything. Ashley,