(j3.2006) (SC22WG5.5134) image selectors

[Bill Long]

On 12/3/13 6:16 PM, Van Snyder wrote:
> On Tue, 2013-12-03 at 18:02 -0600, Bill Long wrote:
>> The identification of the correct physical PE containing the coarray
>> being referenced using the new syntax involves two steps: Using the
>> specified cosubscripts and the current cobounds for the coarray, an
>> image index is computed. The image index is then converted to a
>> physical PE by a team-specific mapping.
>
> This is an important step that is not explained in the TS, or at least
> if it is, I couldn't find it.  It needs to be in Subclause 5.1.
>

OK.  Reinhold's revised ballot reworded this idea in terms of the image 
index in the initial team rather than physical processors.  That is 
arguably better terminology to use.  The image's image index in the 
initial team never changes throughout the program execution.

I think a key point here is that the image is physically unchanged by 
changing teams - it is still executing on the same processor/thread and 
has all the same variables as before.  What changes are the current 
number of images and the current  image index (i.e the values of 
NUM_IMAGES() and THIS_IMAGE()).  As side effects, the scope of 
collective operations is (possibly) changed (if the number of images 
changed), and the mapping from image index to physical processor 
(probably) changed because the image index value (probably) changed but 
the underlying processor/thread did not.

Cheers,
Bill

-- 
Bill Long                                           longb at cray.com
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