Print

---

(also posted to comp.lang.fortran).

I'm trying to write a short demo coarray program
illustrating a race condition.
I find that I cannot do it with ifort v.15
because it seems to apply image synchronisation
even when it's not in the code.
Is this an allowed compiler behaviour?
I think probably yes, but wanted to check.

Here's my example:

% cat z.f90 
program swap
use iso_fortran_env, only: output_unit
implicit none
integer :: img, i[*]
 img = this_image()
   i = img
 if ( img .eq. 1 ) then
   read (*,*)
   i = i[ num_images() ]
 end if
 if ( img .eq. num_images() ) then
   i = i[ 1 ]
 end if
 write (output_unit,*) img, "kuku"
end program swap
% setenv FOR_COARRAY_NUM_IMAGES 4
% ifort -coarray -O0 z.f90

(note the noopt flag)

% ./a.out 
           2 kuku
           3 kuku

At this point the execution is paused
waiting for the user input at READ(*,*).

When I hit ENTER, I get the remaining lines:

           1 kuku
           4 kuku

So it seems the compiler recognised that
I'm swapping values between 2 images and
synchronised the exectution segments between
images 1 and 4.

Anyway, I just wanted to ask for confirmation
in this list that such compiler behind the
scenes synchronisation does not violate the
standard.

Thanks

Anton