On Wed, Jan 28, 2009 at 05:58:28PM +0100, Christian Siebert wrote:

Torsten Hoefler wrote:

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p 65, 5.13: The example is good but the current text is bad. It is simply not allowed to call NBC in a different order. If a certain implementation runs into a deadlock does not matter. This would even be on of the better scenarios (i.e. an easy-to-noticeable error). Other implementations could complete both bcasts (because it thinks they match) but provide the wrong data (i.e. the data from the other bcast or even a mixture?) - which is a much harder failure to detect. which example are you referring to? Only Ex 5.24 is on this page and doesn't use NBC (and the phrasing "deadlock" is used correctly there. ah, yes - sorry it's ok then (this was the first example directly after the description of all nonblocking collectives, so somehow I was thinking about Ibcast) ok

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p 70, example 5.31: To me this example is not "per se" illegal. Both operations simply don't match - that's fine. However, it is possible to extent the example so that the final program is still a valid MPI program. Maybe just add sth. like "in this form" or "without additional collectives that match". no, it's not possible to make this correct if both ranks call it at the same time. Remember, blocking and nonblocking colls have the same matching "namespace". Just add "if (0==rank) MPI_Alltoall(...)" before the switch and add "if (1==rank) MPI_Ialltoall(...)" after the switch statement to make this a correct program. citing myself above: "if both ranks call it at the same time". It's clear that you can fix the example by creating dead code. However, such things would change most of the examples (for example, you could resolve the deadlock condition in Ex. 5.25 with a similar approach. You can also put an if(0) {} around the whole switch and have a correct program ;)). Fixing this would distract the reader from the real example. I think it's clear as it is.

BTW: remove the "int"s before the function calls! ;-) uh yes - thanks!

Best, Torsten -- bash$ :(){ :|:&};: --------------------- http://www.unixer.de/ ----- Torsten Hoefler | Postdoctoral Researcher Open Systems Lab | Indiana University 150 S. Woodlawn Ave. | Bloomington, IN, 474045, USA Lindley Hall Room 135 | +01 (812) 855-3608