hexyz/lib/memory.lua

-- the garbage collector decides when to run its cycles on its own, and this can cause frame spikes in your game.
-- lua provides some amount of control over its garbage collector.
--
-- by storing the average time it takes for a full gc cycle to run, we can check at the end of a frame if we have enough time
-- to run it for 'free'
--
-- if you wish, you can call 'collectgarbage("stop")', and then:
--  at the start of each game frame, call and cache the results of 'am.current_time()' - am.frame_time doesn't seem to work as well
--  at the end of each game frame, call 'check_if_can_collect_garbage_for_free()' with the cached frame time and a desired minimum fps
--
local garbage_collector_cycle_timing_history = {}
local garbage_collector_average_cycle_time = 0
function run_garbage_collector_cycle()
    local time, result = fprofile(collectgarbage, "collect")

    table.insert(garbage_collector_cycle_timing_history, time)
    -- re-calc average gc timing
    local total = 0
    for _,v in pairs(garbage_collector_cycle_timing_history) do
        total = total + v
    end
    garbage_collector_average_cycle_time = total / #garbage_collector_cycle_timing_history
end

function check_if_can_collect_garbage_for_free(frame_start_time, min_fps)
    -- often this will be polled at the end of a frame to see if we're running fast or slow,
    -- and if we have some time to kill before the start of the next frame, we could maybe run gc.
    if (am.current_time() - frame_start_time) < (1 / (min_fps or 60) + garbage_collector_average_cycle_time) then
        run_garbage_collector_cycle()
    end
end