Caching Basics with Parallel

local cache = {}

-- Function that returns a function to cache a single slot of a chest.
local function cache_item(chest, slot)
  return function()
    -- get detailed info about this one slot
    local detail = chest.getItemDetail(slot)

    -- If there is still an item in that slot (slots can change between calls!)...
    if detail then
      -- cache it.
      cache[detail.name] = detail.displayName
    end
  end
end

--- Return a function that goes through a chest and caches all slots.
--- In total, this method should take two ticks to run, since it's all parallel.
--- Be careful of large inventory networks! If you have more than 255 inventory slots, this will overflow the event queue and stall the program.
--- In that case, you may wish to make this function non-parallel.
local function cache_items(chest)
  return function()
    local funcs = {} -- a list of functions to parallelize

    -- for each slot with an item...
    for slot, item in pairs(chest.list()) do
      -- if we haven't cached this item yet...
      if not cache[item.name] then
        -- Add a caching function to the list of functions we want to run in parallel.
        table.insert(funcs, cache_item(chest, slot))
      end
    end

    -- run all the functions in parallel.
    parallel.waitForAll(table.unpack(funcs))
  end
end

-- go through every inventory on the network and cache it, in parallel.
local function cache_network()
  local inventories = {peripheral.find("inventory")} -- a list of all inventories on the network
  local funcs = {} -- a list of functions to parallelize

  for i, inventory in ipairs(inventories) do
    table.insert(funcs, cache_items(inventory))
  end

  -- run all the functions in parallel
  parallel.waitForAll(table.unpack(funcs))
end

-- Then, at the start of your program you can
cache_network()

-- Then, whenever you need the displayName of an item, you can use this:
local display_name = cache[item_name] -- where item_name can be like "minecraft:dirt" or "minecraft:stone"

-- If the item is not in the cache, you can manually cache it (assuming you have the chest and slot still):
cache_item(chest, slot)() -- Note the extra parenthesis at the end.