[Bug libfortran/48587] Avoid exhausting unit number with NEWUNIT=

[jb at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48587

--- Comment #4 from Janne Blomqvist <jb at gcc dot gnu.org> 2011-04-14 08:12:33 UTC ---
(In reply to comment #3)
> I suppose one could put an OPEN .. CLOSE in a DO LOOP and see what happens now.

With gfortran 4.4.3 on Linux 2.6.32, /tmp on ext4, single SATA disk, and 2.67
GHz Xeon X3450 CPU, the following program

program twobfiles
  implicit none
  integer, parameter :: dp = kind(1.0d0)
  integer :: ii, cnt, cnt2, cnt_rate
  real(dp) :: elapsed
  call system_clock(cnt, cnt_rate)
  do ii = 10, 10010
     open(unit=ii, status="scratch")
     close(ii)
  end do
  call system_clock(cnt2)
  elapsed = real((cnt2 - cnt), dp) / cnt_rate
  print *, "Estimate for opening and closing 2 billion files: ", &
       elapsed * 2._dp**31 / 10000, " s."
end program twobfiles

estimates around 10 hours. I suspect current trunk and changing the code to use
NEWUNIT= are in the same ballpark.