[DahkCeles]

This function takes a workload and chips away at it, moving to the next frame after a budgeted amount of time. The budget is set to 50% of the target FPS, or 50% of the current FPS (if there is no target).

Better alternatives might check after X iterations, or sample the frame rate at more than a single point and maybe average it out.

--  Budgets 50% of target or current FPS to perform a workload. 
--  finished = start(workload, onFinish, onDelay)
--  Arguments:
--      workload        table       Stack (last in, first out) of functions to call.
--      onFinish        function?   Optional callback when the table is empty.
--      onDelay         function?   Optional callback each time work delays to the next frame.
--  Returns:
--      finished        boolean     True when finished without any delay; false otherwise.
local function start(workload, onFinish, onDelay)
    local maxDuration = 500/(tonumber(C_CVar.GetCVar("targetFPS")) or GetFrameRate())
    local startTime = debugprofilestop()
    local function continue()
        local startTime = debugprofilestop()
        local task = tremove(workload)
        while (task) do
            task()
            if (debugprofilestop() - startTime > maxDuration) then
                C_Timer.After(0, continue)
                if (onDelay) then
                    onDelay()
                end
                return false
            end
            task = tremove(workload)
        end
        if (onFinish) then
            onFinish()
        end
        return true
    end
    return continue()
end

And here is the testing code I used to make sure it works...

-- Simple testing code
-- /sillyloop           Runs a brief atomic workload (same as /sillyloop 1)
-- /sillyloop 0         Runs an empty workload
-- /sillyloop 10000     Runs a long workload with 10000 parts
-- This overwrites existing workloads, so call /sillyloop to stop an ongoing workload
 
local workload = {}
 
local function sillyLoop()
    local x=1
    for i=1, 10000 do
        x = x+1+2+3+4+5+6+7+8+9
        x = x-1-2-3-4-5-6-7-8-9
        x = x/2/3/4/5/6/7/8/9
        x = x*i*2*3*4*5*6*7*8*9
    end
    
end
 
SlashCmdList["DEBUG_SILLYLOOP"] = function(msg)
    wipe(workload)
    for i=1, tonumber(msg) or 1 do
        workload[i] = sillyLoop
    end
    local overallStart = debugprofilestop()
    start(
        workload,
        function() print("done!") end,
        function() print(#workload.." remaining after "..("%.2d"):format(debugprofilestop()-overallStart)/1000) end
    )
end
SLASH_DEBUG_SILLYLOOP1 = "/sillyloop"