Buffer system not works

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#1

I am creating a game with a queue system, I have created a module that stores the queue number of the players. So I decide to write it using a buffer

local USER_ID_SIZE = 4 -- 4 bytes

local Module = {}
Module.buffer = buffer.create(112)
Module.MaxOffset = 0

function Module.Write(UserId: number?, position: number?, offset: number?)
 local offset = offset or USER_ID_SIZE * (position - 1)
 
 if UserId then
  Module.MaxOffset = math.max(Module.MaxOffset, offset)
  buffer.writeu32(Module.buffer, offset, UserId)
 else
  for i = offset, Module.MaxOffset, USER_ID_SIZE do
   Module.Write(Module.Read(i+USER_ID_SIZE), nil, i)
  end
  Module.MaxOffset = math.max(Module.MaxOffset - USER_ID_SIZE, 0)
 end
end

function Module.Read(position: number): number
 local offset = USER_ID_SIZE * (position - 1)
 return buffer.readu32(Module.buffer, offset)
end

function Module.IsFree(position: number): boolean
 return Module.Read(position) == 0
end

return Module

Call:

local buf = require(game.ServerScriptService.Core.PlacesInfo) 
buf.Write(111, 1) 
buf.Write(222, 2) <--\
buf.Write(333, 3) ---/
buf.Write(nil, 2) 
print(buf.Read(2)) -- 333
print(buf.Read(3)) -- 0

it should be like this: after I set position 2 to nil, the value under position 3 would move to it, but it doesn’t work.

#2

I belive you cannot write the same buffer position more than 1 time.
Seeing this it’s probably shifting because you cannot write a nil value in a buffer.
The problem I see it’s in the else, the position cannot be nil because you are substracting one from the position on the first place and you cannot multiply a number for a nil value.
The rest of the code doesen’t seem off place, I would consider changing the write part where you call the nil value.

Hope this helps.

1 Like
#3

I would recommend not using buffers at all unless you really need to optimize memory usage. It’ll just make things more complicated than it needs to be with no real benefit.

#4

You can, it will just overwrite whatever bits are stored at that position

The nil aspect is weird though, this line

  for i = offset, Module.MaxOffset, USER_ID_SIZE do
   Module.Write(Module.Read(i+USER_ID_SIZE), nil, i)
  end

Should cause an error since it will try to do nil - 1 on the first line of the Write function. I don’t know why OP is not getting an error

I don’t understand what is wrong. When you set 2 to nil, the value at position 3 is moved to position 2, as seen by print(buf.Read(2)) -- 333, which is typical behavior for queues (and how table.remove() does it)
By “the value under position 3”, do you mean like position 1 would move to position 3?

You might be able to use buffer.copy to move the whole upper values of the buffer down by UDER_ID_SIZE rather than doing it one value at a time. However I have not tested buffer.copy where the target and the source are the same buffer, and if that causes some edge case

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#5

I noticed that my Read function takes a position, not an offset.
and in the loop, I’m sending an offset there, not a position