Rate Limiting in Co-array Fortran

program rate_limiting
  use iso_fortran_env, only: int64
  implicit none
  
  integer :: i, req
  integer, parameter :: num_requests = 5
  integer :: requests(num_requests)[*]
  real(kind=8) :: start_time, current_time
  
  ! First we'll look at basic rate limiting. Suppose
  ! we want to limit our handling of incoming requests.
  ! We'll serve these requests off an array.
  
  do i = 1, num_requests
    requests(i) = i
  end do
  
  ! This limiter will pause execution for 200 milliseconds.
  ! This is the regulator in our rate limiting scheme.
  
  call cpu_time(start_time)
  
  ! By pausing before serving each request, we limit ourselves to
  ! 1 request every 200 milliseconds.
  
  do i = 1, num_requests
    call sleep(0.2)
    call cpu_time(current_time)
    print *, "request", requests(i), "at time", current_time - start_time
  end do
  
  ! We may want to allow short bursts of requests in
  ! our rate limiting scheme while preserving the
  ! overall rate limit. We can accomplish this by
  ! using a counter and allowing a certain number of
  ! requests to proceed without delay.
  
  integer :: burst_counter
  burst_counter = 3
  
  ! Now simulate 5 more incoming requests. The first
  ! 3 of these will benefit from the burst capability.
  
  do i = 1, num_requests
    if (burst_counter > 0) then
      burst_counter = burst_counter - 1
    else
      call sleep(0.2)
    end if
    call cpu_time(current_time)
    print *, "bursty request", i, "at time", current_time - start_time
  end do
  
end program rate_limiting

This Co-array Fortran program demonstrates rate limiting, an important mechanism for controlling resource utilization and maintaining quality of service. The program uses simple timing and sleep functions to implement rate limiting.

In the first part, we simulate handling 5 requests with a fixed rate limit of one request every 200 milliseconds. We use the sleep subroutine to pause execution between requests.

In the second part, we implement a basic form of bursty rate limiting. We allow the first 3 requests to proceed immediately (simulating a burst), and then apply the rate limit to subsequent requests.

To run the program, save it as rate_limiting.f90 and compile it with a Fortran compiler that supports Co-array Fortran. For example:

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

The output will show the requests being processed with the appropriate delays. The exact timing may vary slightly due to system-specific factors.

Note that this is a simplified demonstration of rate limiting concepts. In a real-world scenario, you might use more sophisticated timing mechanisms and possibly leverage Co-array Fortran’s parallel capabilities for distributed rate limiting.

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Rate Limiting in Co-array Fortran