【高级技巧】分段锁：大表写入的分段互斥

local SEG = 16
local segBusy = {}
local function segOf(key)
    local sum = 0
    for i = 1, #key do
        sum = sum + string.byte(key, i)
    end
    return sum % SEG
end
local function withLock(key, fn)
    local s = segOf(key)
    while segBusy[s] do
        coroutine.yield()
    end
    segBusy[s] = true
    local ok, err = pcall(fn)
    segBusy[s] = nil
    if not ok then
        error(err)
    end
end

local function depositItem(guildName, itemLine)
    withLock(guildName, function()
        local blob = getsysvar("GuildBag_" .. guildName) or ""
        setsysvarex("GuildBag_" .. guildName,
            blob .. itemLine .. ";", 1)
    end)
end