Timers in Co-array Fortran

program timers
  use iso_fortran_env
  implicit none

  ! We often want to execute code at some point in the future, or repeatedly 
  ! at some interval. Co-array Fortran doesn't have built-in timer features, 
  ! but we can use the SLEEP intrinsic to simulate timers.

  ! Simulate a timer that waits for 2 seconds
  call sleep(2)
  print *, "Timer 1 fired"

  ! If you just wanted to wait, you could have used SLEEP directly.
  ! One reason a timer might be useful is that you can potentially 
  ! cancel it before it fires. Here's an example of that concept:

  logical :: stop2
  stop2 = .false.

  ! Start a "timer" in a separate image
  sync all
  if (this_image() == 1) then
    call sleep(1)
    if (.not. stop2) then
      print *, "Timer 2 fired"
    end if
  end if

  ! On image 2, we "stop" the timer
  if (this_image() == 2) then
    stop2 = .true.
    print *, "Timer 2 stopped"
  end if

  ! Give enough time for the "timer" to fire, if it was going to
  sync all
  if (this_image() == 1) then
    call sleep(2)
  end if

end program timers

To compile and run this Co-array Fortran program:

$ caf timers.f90 -o timers
$ cafrun -np 2 ./timers
Timer 1 fired
Timer 2 stopped

The first “timer” will fire ~2s after we start the program, but the second should be stopped before it has a chance to fire.

Note that this is a simplified simulation of timers using Co-array Fortran. The language doesn’t have built-in timer features like some other languages, so we use the SLEEP intrinsic and co-arrays to demonstrate similar concepts. The “stopping” of a timer is simulated using a logical variable shared across images.

In a real-world scenario, you might want to use more sophisticated methods for timing and synchronization, possibly involving MPI libraries or other external timing mechanisms, depending on your specific requirements and the capabilities of your Fortran compiler and runtime environment.

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Timers in Co-array Fortran