# Changes _smp_build_ncpus depending on various factors
#
# -c cpus  constrains the CPU count to "cpus"
# -m mem   constrains the CPU count to the total amount of memory in the system
#          (in megabytes) divided by "mem", rounded down
#
# If no options are passed, sets _smp_build_ncpus to 1.
# _smp_build_ncpus will never be raised, only lowered.
%constrain_build(c:m:) %{lua:
  local mem_limit = math.tointeger(opt.m)
  local cpu_limit = math.tointeger(opt.c)
  local current_cpus = math.tointeger(macros._smp_build_ncpus)
  local constrained_cpus = current_cpus

  -- Parse meminfo to find the total amount of memory in the system
  local function getmem()
    local mem = 0
    for l in io.lines('/proc/meminfo') do
      if l:sub(1, 9) == "MemTotal:" then
        mem = math.tointeger(string.match(l, "MemTotal:%s+(%d+)"))
        break
      end
    end
    return mem
  end

  if (not cpu_limit and not mem_limit) then
    cpu_limit = 1
  end

  if cpu_limit ~= nil then
    constrained_cpus = math.min(cpu_limit, constrained_cpus)
  end
  if mem_limit ~= nil then
    local mem_total = getmem(verbose)
    local limit = math.max(1, mem_total // (mem_limit * 1024))
    constrained_cpus = math.min(constrained_cpus, limit)
  end

  macros._smp_build_ncpus = constrained_cpus
}