(j3.2006) (SC22WG5.3622) [ukfortran] A comment on John Wallin's comments on Nick MacLaren's comments

[N.M. Maclaren]

On Nov 5 2008, Van Snyder wrote:
>
>I remarked on this problem before m185, and proposed a trivial addition
>to the OPEN statement to allow message passing using I/O statements,
>which already know how to do DTIO and asynchronous, in 08-204.  Subgroup
>didn't even consider it.
>
>If coarrays are kicked off the train in Tokyo, we really should go back
>and look at the directions proposed in 08-204 and 08-205.  Fortran I/O
>applied to message passing should provide all the basic functionality of
>MPI, and would be far clearer.

Er, no.  They would provide the point-to-point functionality, but that is
not quite the same.  In my MPI course, I teach collectives as the basic
functionality, and point-to-point as the specialist feature!

However, I am not saying that internal FIFOs aren't a good communication
mechanism - far from it - merely that MPI is more than that.

>Within a single SMP, say a dual quad-core PC, one can already accomplish
>what's proposed in 08-204 with a pipe, but I haven't met a system yet
>where pipes work across NFS.  08-204 provides syntax for users to hook
>to stuff that vendors provide that go beyond NFS.  08-205 provides a way
>for users to roll their own, perhaps atop MPI, while hiding the ugly
>details behind I/O statements.

I am not quite sure what you mean. The basic FIFO aspect of pipes is 
preserved across NFS - if you are referring to multiple sources or multiple 
sinks, that is going a bit beyond pipes. And, of course, there is nothing 
stated about when data is transferred - but that is true even of local 
pipes.

What definitely is the case is that the metadata and contents can get out of
of sync in NFS version 3, even in the simplest configurations.  But a pure 
pipe doesn't rely on stat().

Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679