koreader/frontend/document/doccache.lua

--[[
"Global" LRU cache used by Document & friends.
--]]

local Cache = require("cache")
local CanvasContext = require("document/canvascontext")
local DataStorage = require("datastorage")
local logger = require("logger")

local function calcCacheMemSize()
    local min = DGLOBAL_CACHE_SIZE_MINIMUM
    local max = DGLOBAL_CACHE_SIZE_MAXIMUM
    local calc = Cache:_calcFreeMem() * (DGLOBAL_CACHE_FREE_PROPORTION or 0)
    return math.min(max, math.max(min, calc))
end
local cache_size = calcCacheMemSize()


local function computeCacheSize()
    local mb_size = cache_size / 1024 / 1024

    -- If we end up with a not entirely ridiculous cache size, use that...
    if mb_size >= 8 then
        logger.dbg(string.format("Allocating a %dMB budget for the global document cache", mb_size))
        return cache_size
    else
        return nil
    end
end

local function computeCacheSlots()
    local mb_size = cache_size / 1024 / 1024

    --- ...otherwise, effectively disable the cache by making it single slot...
    if mb_size < 8 then
        logger.dbg(string.format("Setting up a minimal single slot global document cache"))
        return 1
    else
        return nil
    end
end

local DocCache = Cache:new{
    slots = computeCacheSlots(),
    size = computeCacheSize(),
    -- Average item size is a screen's worth of bitmap, mixed with a few much smaller tables (pgdim, pglinks, etc.), hence the / 3
    avg_itemsize = math.floor(CanvasContext:getWidth() * CanvasContext:getHeight() * (CanvasContext.is_color_rendering_enabled and 4 or 1) / 3),
    -- Rely on CacheItem's eviction callback to free resources *immediately* on eviction.
    enable_eviction_cb = true,
    disk_cache = true,
    cache_path = DataStorage:getDataDir() .. "/cache/",
}

return DocCache