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From: booker%network@ucsd.edu (Booker bense)
Newsgroups: comp.lang.fortran,comp.parallel
Subject: Re: Parallel Fortran question
Message-ID: <12251@hubcap.clemson.edu>
Date: 13 Dec 90 21:02:20 GMT
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Organization: San Diego Supercomputer Center @ UCSD
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In article <12191@hubcap.clemson.edu> john%ghostwheel.unm.edu@ariel.unm.edu (John Prentice) writes:
>I want to code the following for a shared memory parallel system:
>
>      program yuppie
>c
>c        loop over subroutine
>c
>      integer n,nmax
>      parameter (nmax=10)
>      real hippie(nmax)
>      do 10 n=1,nmax
>          call yippie (hippie(n))
>                  .
>          call yippie (hippie(n))
>                  .
>   10 continue
>      end
>      subroutine yippie (hippie)
>      real hippie
>      logical first
>      save first
>      data first /.true./
>c
>      if (first) then
>          .
>        [initializations]
>          .
>          first=.false.
>      endif
>        .
>      end
>
>When yippie gets called the first time, it does some initializations.
>Subsequent calls for the same loop iteration should not repeat the
>initialization however (assume I am parallelizing the loop in the main
>routine).  The way I wrote yippie works fine on a non-shared memory
>machine, but not on a shared memory system.  This is because the save
>statement causes yippie to always save first to the same memory location,
>no matter which processor is being used.  On the Cray, you could use task
>common to save the value of first, but there is no way to initialize task
>common (that I know of).  Any suggestions?  Thanks.
>


- 
A better way to do this for a shared memory machine is to put first
into the arguements for the subroutine. i.e. 
 
	
     do 10 n=1,nmax
	  first = .true. 
          call yippie (hippie(n),first)
          first = .false.
                  .
                  .
                  .
          call yippie (hippie(n),first)
                  .
                  .
                  .
	  
    10 continue
  
And make first a local ( or non-shared or private ) variable. If you
are using the CRI autotasking directives, something like

CMIC$ DO ALL SHARED( hippie ) PRIVATE(first,n)

 I'm assuming that you need first = true for each n ,i.e.  first means
first call in the do loop. I quess you said this didn't you. 




-Booker C. Bense
/* benseb@grumpy.sdsc.edu */