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