[maqjav]

This is the code I wrote with your ideas:

local Routine = {} do   
    function Routine:Init(getterItems, chunkSize)
        self.context, self.deadline = {}
        self.context.currentIndex = 1
        self.context.getterItems = getterItems 
        self.context.chunkSize = chunkSize
    end
 
    function Routine:Run(callback)
        if (not self.context) then
            return true
        end
        self.deadline = debugprofilestop() + 500/(tonumber(C_CVar.GetCVar("targetFPS")) or GetFrameRate() or 35)
 
        repeat
            local totalIndex = 1
            local chunkIndex = 1
            for key, value in pairs(self.context.getterItems()) do
                if (totalIndex >= self.context.currentIndex) then
                    if (chunkIndex == self.context.chunkSize) then
                        return false
                    end
                    
                    callback(self.context, key, value)
                    self.context.currentIndex = self.context.currentIndex + 1
                    chunkIndex = chunkIndex + 1
                end
                
                totalIndex = totalIndex + 1
            end
            
            self.context.finished = true
            return true
        until debugprofilestop() > self.deadline
    end
    
    function Routine:IsRunning()
        if self.context and not self.context.finished then
            return true
        end
        return false
    end
    
    function Routine:Reset()
        self.context = {}
    end
    
    function Routine:New(routine)
        routine = routine or {}
        setmetatable(routine, self)
        self.__index = self
        return routine
    end
end

And this is how I use it:

local routine = Routine:New()
routine:Init(GetStuff, 100)
 
-- Using OnUpdate script
myFrame:SetScript("OnUpdate", function(self)
    local finished = routine:Run(function(state, key, value)
        doHeavyStuff(key, value)
    end)
    
    if (finished) then
        routine:Reset()
        self:SetScript("OnUpdate", nil)
    end
end);
 
-- Using a ticker if the frame is hidden
C_Timer.NewTicker(0.5, function(self)
    local finished = routine:Run(function(context, key, value)
        doHeavyStuff(key, value)
    end)
    
    if (finished) then
        routine:Reset()
        self:Cancel()
    end
end

So far this improves the performance a lot. It takes longer to finish, but I'm sure I can improve it changing the value of "state.chunkSize".

The issue I find with this code is that it loops through the table returned by GetStuff() several times and I don't see how to avoid it.

Thank you both!