Finding and fixing memory leaks in FiveM resources

A resource that uses 2 MB after a restart and 200 MB six hours later is leaking. Lua has a garbage collector, so leaks in FiveM scripts are almost never lost memory — they are data your code keeps a reference to and never lets go: a table keyed by player that nobody cleans, a cache without a limit, an event handler added again on every call.

CreateThread(function()
    while true do
        Wait(300000)
        print(('[%s] Lua memory: %.1f MB'):format(GetCurrentResourceName(), collectgarbage('count') / 1024))
    end
end)

Short spikes are normal — the collector runs in steps. A line that keeps rising across hours is a leak. Resmon shows per-resource numbers on the client — see resmon explained.

local sessions = {}

AddEventHandler('playerDropped', function()
    sessions[source] = nil
end)

local cache, order, MAX = {}, {}, 500
local function remember(key, value)
    if not cache[key] then
        order[#order + 1] = key
        if #order > MAX then cache[table.remove(order, 1)] = nil end
    end
    cache[key] = value
end

AddEventHandler('onResourceStop', function(res)
    if res ~= GetCurrentResourceName() then return end
    -- delete entities, blips and zones created by this resource
end)

Handlers registered inside loops are also a correctness bug: each one fires, so events run several times. Event basics: events explained.

• Props and peds spawned for effects and never deleted.
• NUI elements created on every message and never removed.
• Streamed textures requested repeatedly without releasing them.
• ox_lib points and zones created on every enter instead of once.