Channel Buffering in Co-array Fortran

program channel_buffering
  use iso_fortran_env
  implicit none

  integer :: status
  character(len=20) :: messages(2)[*]
  integer :: images

  ! By default, co-arrays in Fortran are distributed across images,
  ! which can be thought of as similar to Go's unbuffered channels.
  ! However, we can simulate a buffered channel by using a local array
  ! on a single image.

  ! Here we create a co-array of strings that can hold up to 2 values.
  ! We'll only use it on image 1 to simulate a buffered channel.
  images = num_images()

  if (this_image() == 1) then
    ! Because we're simulating a buffered channel, we can send these
    ! values into the array without a corresponding concurrent receive.
    messages(1) = "buffered"
    messages(2) = "channel"

    ! Later we can receive these two values as usual.
    print *, trim(messages(1))
    print *, trim(messages(2))
  end if

  sync all

end program channel_buffering

To run the program, save it as channel_buffering.f90 and use your Fortran compiler. For example, with gfortran:

$ gfortran -coarray=single channel_buffering.f90 -o channel_buffering
$ ./channel_buffering
buffered
channel

In this Co-array Fortran version, we’ve simulated Go’s buffered channel using a co-array. Co-array Fortran doesn’t have a direct equivalent to Go’s channels, but co-arrays provide a way to share data between images (similar to processes), which can be used for communication.

We create a co-array of strings that can hold two messages. To simulate the buffered behavior, we only use this array on the first image (equivalent to the first process). We then write to and read from this array, mimicking the behavior of sending to and receiving from a buffered channel in Go.

The sync all statement at the end ensures all images have completed their execution before the program terminates, which is important in more complex co-array programs.

Note that this is a simplified simulation of Go’s buffered channels. In a real Co-array Fortran program, you would typically use co-arrays for inter-image communication, which can be more complex but also more powerful for parallel programming.