Channels in Fortran

In Fortran, we don’t have direct equivalents to Go’s channels and goroutines. However, we can use Fortran’s coarrays for inter-image communication, which provides a form of parallel processing. Here’s an example that demonstrates a similar concept:

program channels_example
  use iso_fortran_env, only: team_type
  implicit none

  character(len=10) :: message
  type(team_type) :: new_team

  ! Create a new team with two images
  call form_team(2, new_team)

  if (this_image() == 1) then
    ! This is equivalent to "sending" a message
    message = "ping"
    sync images(2)
  else if (this_image() == 2) then
    ! This is equivalent to "receiving" a message
    sync images(1)
    print *, message
  end if

end program channels_example

In this Fortran program, we’re using coarrays and image synchronization to mimic the behavior of channels in Go.

1. We use the iso_fortran_env module to access the team_type derived type, which we’ll use to create a team of images.

2. We declare a message variable to hold our “ping” string.

3. We create a new team with two images using form_team(2, new_team). This is somewhat analogous to creating a channel in Go.

4. We use this_image() to determine which image (similar to a thread or process) is currently executing.

5. In image 1 (equivalent to the sender in Go):

   • We set the message to “ping”.
   • We use sync images(2) to synchronize with image 2, effectively “sending” the message.

6. In image 2 (equivalent to the receiver in Go):

   • We use sync images(1) to wait for image 1 to be ready.
   • We then print the message, which has been set by image 1.

To run this program, you would compile it with a Fortran compiler that supports coarrays, and then run it with at least two images. For example:

$ gfortran -fcoarray=lib channels_example.f90 -lcaf_mpi
$ cafrun -np 2 ./a.out
ping

This program demonstrates a basic form of inter-image communication in Fortran, which is conceptually similar to channel communication in Go. However, it’s important to note that Fortran’s coarray model is different from Go’s channel model, and has its own set of rules and best practices for parallel programming.