Stateful Goroutines in Co-array Fortran

module stateful_coarrays
  implicit none
  private

  type :: read_op
    integer :: key
    integer :: resp
  end type read_op

  type :: write_op
    integer :: key
    integer :: val
    logical :: resp
  end type write_op

  type(read_op), allocatable :: reads(:)[:]
  type(write_op), allocatable :: writes(:)[:]
  integer :: state(5)[*]
  integer(kind=8) :: read_ops[*] = 0
  integer(kind=8) :: write_ops[*] = 0

  public :: initialize, run_stateful_coarray, report_results

contains

  subroutine initialize()
    allocate(reads(100)[*])
    allocate(writes(10)[*])
  end subroutine initialize

  subroutine run_stateful_coarray()
    integer :: i, key, val
    real :: r

    do i = 1, 100
      call random_number(r)
      key = int(r * 5) + 1
      reads(i)%key = key
      reads(i)%resp = state(key)
      read_ops = read_ops + 1
      call sleep(1)
    end do

    do i = 1, 10
      call random_number(r)
      key = int(r * 5) + 1
      call random_number(r)
      val = int(r * 100)
      writes(i)%key = key
      writes(i)%val = val
      state(key) = val
      writes(i)%resp = .true.
      write_ops = write_ops + 1
      call sleep(1)
    end do
  end subroutine run_stateful_coarray

  subroutine report_results()
    if (this_image() == 1) then
      print *, "readOps:", read_ops
      print *, "writeOps:", write_ops
    end if
  end subroutine report_results

end module stateful_coarrays

program main
  use stateful_coarrays
  implicit none

  call initialize()
  call run_stateful_coarray()
  sync all
  call report_results()
end program main

This example demonstrates how to implement stateful operations using Co-array Fortran. Co-array Fortran provides a parallel programming model that allows for shared memory-style programming in a distributed memory environment.

In this implementation:

We define two derived types read_op and write_op to encapsulate read and write operations.
We use co-arrays for reads, writes, state, read_ops, and write_ops to allow sharing of data across images (parallel processes).
The run_stateful_coarray subroutine simulates the behavior of multiple goroutines performing read and write operations. It uses random number generation to simulate the random access pattern.
Instead of channels, we directly modify the shared state co-array and update the operation counters.
The sleep calls simulate the time delay between operations.
The report_results subroutine prints the final operation counts, but only on the first image to avoid duplicate output.

To run this program:

$ gfortran -fcoarray=single stateful_coarrays.f90 -o stateful_coarrays
$ ./stateful_coarrays

Note that this implementation uses a single-image coarray model for simplicity. In a real-world scenario, you would typically run this across multiple images to take advantage of parallelism:

$ gfortran -fcoarray=lib stateful_coarrays.f90 -o stateful_coarrays -lcaf_mpi
$ cafrun -np 4 ./stateful_coarrays

This Co-array Fortran version provides a different approach to managing shared state compared to the original example. Instead of using goroutines and channels, it uses co-arrays to share data across parallel processes. The synchronization is implicit in the co-array operations, providing a different model for concurrent programming.

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Stateful Goroutines in Co-array Fortran