【高级技巧】乐观锁：版本号比对的安全写入

local function loadRecord(key)
    local blob = tostring(getsysvar(key) or "")
    local ver, data = string.match(blob, "^(%d+)|(.*)$")
    return tonumber(ver) or 0, data or ""
end
local function saveRecord(key, ver, data)
    local curVer = loadRecord(key)
    if curVer ~= ver then
        return false
    end
    setsysvarex(key, (ver + 1) .. "|" .. data, 1)
    return true
end

local function updateNotice(key, newNotice)
    for attempt = 1, 3 do
        local ver = loadRecord(key)
        if saveRecord(key, ver, newNotice) then
            return true
        end
    end
    return false
end