ISO/IEC JTC1/SC22/WG5 N1863

           Requirements for TS on further coarray features 

                           John Reid

                          30 June 2011

Resolution LV5 of the WG5 meeting in Las Vegas, Feb. 2008 reads:
"LV5.  Content and processing of TR on Enhanced Coarray Facilities
That WG5 declares that the content of the Technical Report on Enhanced
Coarray Facilities in Fortran is as shown in document J3/08-131r1.
Further, WG5 expects the TR to be published during the second quarter
of 2011."  

The features of J3/08-131r1 are:

1) Collective intrinsic subroutines:
   CO_ALL
   CO_ANY
   CO_COUNT
   CO_MAXLOC
   CO_MAXVAL
   CO_MINLOC
   CO_MINVAL
   CO_PRODUCT
   CO_SUM

2) Teams and features that require teams: 
   Team formation and inquiry; FORM_TEAM, TEAM_IMAGES intrinsics,
         and the IMAGE_TEAM type.
   SYNC TEAM statement
   TEAM specifiers in I/O statements
      
3) The NOTIFY and QUERY statements.

4) File connected on more than one image, except for the files
   preconnected to the units specified by OUTPUT_UNIT and ERROR_UNIT.

A draft TR, containing exactly these features, is visible as J3/11-176
or N1858. 

Some latitude on the technical content seems appropriate. We discuss 
each item of the list in turn.

1) Collective procedures are needed in order that portable codes can use 
efficient methods for commonly occurring calculations that demand 
collaboration among images. How this is best done may depend on the 
details of the architure. The set of collective subroutines was based on
mirroring the transformational functions of Fortran 2008. Alternatives,
such as those of proposal 1 of N1835, should be considered. In 
particular, there should be a collective procedure for broadcasting and
one that calls user-written code for the underlying operation.  

2) It is not always appropriate for all the images to be engaged in a
single calculations. There is a need to support independent calculations
being performed simultaneously on teams of images. Better ways of 
providing this functionality should be considered. 

3) The NOTIFY and QUERY statements provide additional synchronization
facilities.  Alternatives, such as those of proposal 9 of N1835, should 
be considered. 

4) There is a need for features to support I/O in parallel. Alternatives 
should be considered.   

It is not the intention to provide significant extra facilities beyond 
those of the four items of this list.