10.3.1.4 I/O With Explicit Parallelization

You can do I/O in a loop that executes in parallel, provided that:

• It does not matter that the output from different threads is interleaved (program output is nondeterministic.)

• You can ensure the safety of executing the loop in parallel.

Example: I/O statement in loop

!$OMP PARALLEL DO PRIVATE(k)
      do i = 1, 10     !  Parallelized
        k = i
        call show ( k )
      end do
      end
      subroutine show( j )
      write(6,1) j
1      format(’Line number ’, i3, ’.’)
      end
demo% f95 -openmp t13.f
demo% setenv PARALLEL 4
demo% a.out

Line number 9.
Line number 4.
Line number 5.
Line number 6.
Line number 1.
Line number 2.
Line number 3.
Line number 7.
Line number 8.

However, I/O that is recursive, where an I/O statement contains a call to a function that itself does I/O, will cause a runtime error.