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ringbuffer

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ringbuffer

unidirectional cdata ring buffers


local ringbuffer = require'ringbuffer'

Unidirectional cdata array-based ring buffers with the following properties:

  • elements can be added or removed one by one or in bulk.
  • data can only be added to the tail and removed from the head (FIFO).
  • the buffer is fixed-size and can grow on request.
  • can work with an internally allocated byffer, an external buffer, or can be used as an abstract interface over an external API.

API

ringbuffer{size=, ctype=, ...} -> cb create a cdata ring buffer
cb:head(i) -> i normalized offset from head
cb:tail(i) -> i normalized offset from tail (tail is last index + 1)
cb:segments() -> i1, n1, i2, n2 offsets and sizes of buffer's occupied segments
cb:free_segments() -> i1, n1, i2, n2 offsets and sizes of buffer's free segments
cb:push(n[, data]) -> i1, n1, i2, n2 add data to tail, invoking cb:read()
cb:pull(n[, data]) -> i1, n1, i2, n2 remove data from head, invoking cb:write()
cb:checksize(n) grow the buffer to fit at least n more elements
cb:alloc(n) -> cdata allocator (defaults to ffi.new)
cb:read(dst, di, si, n) segment reader (defaults to ffi.copy)
cb:write(src, di, si, n) segment writer (defaults to ffi.copy)
cb.data -> cdata the buffer itself
b.start -> i start index
b.size -> n capacity
b.length -> n occupied size

ringbuffer(cb) -> cb

Convert an initial table to a ring buffer and return it. The table can have fields:

  • size: the size of the buffer.
  • ctype: the element type for allocating an internal buffer, or
  • data: a pre-allocated buffer.
  • start, length: optional, in case the buffer comes pre-filled.
  • alloc: optional custom allocator, for initial allocation and growing.

How it works

When push() is called with a data arg, the write() method is called once or twice with the segments to be written from data into the buffer. When pull() is called with a data arg, the read() method is called once or twice with the segments to be read from the buffer into data.

As an interface

A ring buffer doesn't have to manage an actual buffer. Instead, it can be used to manage an external resource that the ring buffer logic can be applied to. To do this pass data = true when creating a buffer to avoid allocating an actual buffer. Call push() and pull() without a data arg to avoid calls to write() and read() and use the buffer state variables start, length and size as you want. Or, pass true (or any other value) to the data arg in push() and pull() and override read() and write() to do the actual moving of data.

Extending

The ringbuffer function is actually a callable table which can be copied or inherited from and patched to create custom buffer classes.


Last updated: 14 months ago | Edit on GitHub

Pkg type:Lua+ffi
Version: r3-1-g41e1355
Last commit:
License: PD
Requires: luajit 
Required by: none

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