【高级技巧】延迟队列：到期任务的小顶堆调度

local heap = {}
local function heapPush(dueAt, task)
    heap[#heap + 1] = { due = dueAt, task = task }
    local i = #heap
    while i > 1 do
        local p = math.floor(i / 2)
        if heap[p].due <= heap[i].due then
            break
        end
        heap[p], heap[i] = heap[i], heap[p]
        i = p
    end
end
local function heapPop()
    local top = heap[1]
    local last = table.remove(heap)
    if #heap > 0 then
        heap[1] = last
        local i = 1
        while true do
            local l, r, m = i * 2, i * 2 + 1, i
            if l <= #heap and heap[l].due < heap[m].due then
                m = l
            end
            if r <= #heap and heap[r].due < heap[m].due then
                m = r
            end
            if m == i then
                break
            end
            heap[m], heap[i] = heap[i], heap[m]
            i = m
        end
    end
    return top
end

local function onHeapTick()
    while heap[1] ~= nil and heap[1].due <= os.time() do
        local job = heapPop()
        sendmsg(nil, 1, "到期结算：" .. job.task)
    end
end