Implement an LRU cache

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Starbeamrainbowlabs 2021-07-13 23:42:08 +01:00
parent e799a2ea61
commit 81957070f9
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GPG Key ID: 1BE5172E637709C2
3 changed files with 96 additions and 4 deletions

@ -13,6 +13,7 @@ worldeditadditions.Mesh,
worldeditadditions.Face = dofile(worldeditadditions.modpath.."/utils/mesh.lua")
worldeditadditions.Queue = dofile(worldeditadditions.modpath.."/utils/queue.lua")
worldeditadditions.LRU = dofile(worldeditadditions.modpath.."/utils/lru.lua")
dofile(worldeditadditions.modpath.."/utils/strings/init.lua")

@ -0,0 +1,80 @@
local Queue
if worldeditadditions then
Queue = dofile(worldeditadditions.modpath.."/utils/queue.lua")
else
Queue = require("queue")
end
--- A least-recently-used cache implementation.
-- @class
local LRU = {}
LRU.__index = LRU
--- Creates a new LRU cache.
-- Optimal sizes: 8, 16, 32, 64 or any value above
-- @param max_size=32 number The maximum number of items to store in the cache.
-- @returns LRU A new LRU cache.
function LRU.new(max_size)
if not max_size then max_size = 32 end
local result = {
max_size = max_size,
cache = { },
size = 0,
queue = Queue.new()
}
setmetatable(result, LRU)
return result
end
--- Determines whether the given key is present in this cache object.
-- Does NOT update the most recently used status of said key.
-- @param key string The key to check.
-- @returns bool Whether the given key exists in the cache or not.
function LRU:has(key)
return self.cache[key] ~= nil
end
--- Gets the value associated with the given key.
-- @param key string The key to retrieve the value for.
-- @returns any|nil The value associated with the given key, or nil if it doesn't exist in this cache.
function LRU:get(key)
if not self.cache[key] then return nil end
-- Put it to the end of the queue
self.queue:remove_index(self.cache[key].index)
self.cache[key].index = self.queue:enqueue(key)
return self.cache[key].value
end
--- Adds a given key-value pair to this cache.
-- Note that this might (or might not) result in the eviction of another item.
-- @param key string The key of the item to add.
-- @param value any The value to associate with the given key.
-- @returns nil
function LRU:set(key, value)
if self.cache[key] ~= nil then
-- It's already present in the cache - update it
-- Put it to the end of the queue
self.queue:remove_index(self.cache[key].index)
local new_index = self.queue:enqueue(key)
-- Update the cache entry
self.cache[key] = {
value = value,
index = new_index
}
else
-- It's not in the cache -- add it
self.cache[key] = { value = value, index = self.queue:enqueue(key) }
self.size = self.size + 1
if self.size > self.max_size then
-- The cache is full, delete the oldest item
local oldest_key = self.queue:dequeue()
self.cache[oldest_key] = nil
self.size = self.size - 1
end
end
end
return LRU

@ -15,6 +15,7 @@ function Queue:enqueue(value)
local new_last = self.last + 1
self.last = new_last
self.items[new_last] = value
return new_last
end
function Queue:contains(value)
@ -30,15 +31,25 @@ function Queue:is_empty()
return self.first > self.last
end
function Queue:remove_index(index)
self.items[index] = nil
end
function Queue:dequeue()
local first = self.first
if Queue.is_empty(self) then
error("Error: The self is empty!")
end
local value = self.items[first]
self.items[first] = nil -- Help the garbage collector out
self.first = first + 1
local first = self.first
-- Find the next non-nil item
local value
while value == nil do
if first >= self.last then return nil end
value = self.items[first]
self.items[first] = nil -- Help the garbage collector out
first = first + 1
end
self.first = first
return value
end