lds - LuaJIT Data Structures

lds provides data structures which hold LuaJIT cdata.

These containers cover the common use cases of Lua tables:

Array (fixed-size array)
Vector (dynamically-sized array)
HashMap (key-value store)

After installing the library, simply require the module and use the returned value:

local lds = require 'lds'

Manual Installation

This library is currently only available as a GitHub repo. To install, clone the repo and copy lds.lua and the lds directory (the one inside the repo) to somewhere on your LUA_PATH.

# The path   /usr/local/share/lua/5.1  is just an example, it is common on Ubuntu platforms

git clone https://github.com/neomantra/lds.git
cp -r lds/lds.lua lds/lds    /usr/local/share/lua/5.1

LuaRocks Installation

To install from the LuaRocks rockspec:

git clone https://github.com/neomantra/lds.git
luarocks build rockspecs/lds-scm-1.rockspec

This library is NOT officially loaded to the LuaRocks repository.

Example

The following example shows a cdata being stored in a Vector and then retrieved from there are stored in a HashMap.

local ffi = require 'ffi'
local lds = require 'lds'

ffi.cdef([[
struct Item {
    int    id;
    char   name[16];
    int    inventory;
};
]])

local Item_t = ffi.typeof('struct Item')

-- Create a Vector and add some items
local v = lds.Vector( Item_t )
v:push_back( Item_t( 100, 'Apple',  42 ) )
v:push_back( Item_t( 101, 'Orange', 10 ) )
v:push_back( Item_t( 102, 'Lemon',   6 ) )
assert( v:size() == 3 )
assert( v:get(0).id == 100 )
assert( v:get(2).id == 102 )

-- Now create a HashMap of Item id to Item
-- Note this is stored by-value, not by-reference
local map = lds.HashMap( ffi.typeof('int'), Item_t )
for i = 0, v:size()-1 do  -- lds.Vector is 0-based
    local item = v:get(i)
    map:insert( item.id, item )  
end
assert( map:size() == 3 )
assert( map:find(100).key == 100 )
assert( map:find(100).val.inventory == 42 )
assert( map:find(102).key == 102 )
assert( map:find(102).val.inventory == 6 )

Motivation

Lua provides a powerful data structure called a table. A table is an heterogeneous associative array -- its keys and values can be any type (except nil).

The LuaJIT FFI enables the instantiation and manipulation of C objects directly in Lua; these objects called cdata. Although cdata may be stored in Lua tables (but are not suitable as keys), when used this way they are subject to a 4GB memory limit and GC inefficiency.

lds provides the containers Array, Vector, and HashMap, which cover the common use cases of Lua tables. However, the memory of these containers are managed through user-specified allocators (e.g. malloc) and thus are not subject to the LuaJIT memory limit. It is also significantly lower load on the LuaJIT Garbage Collector.

One drawback to be aware of is that lds containers are homogeneous. A given container has explicitly one key type and one cdata value type.

API

Documentation for this library is pretty sparse right now -- try reading the test scripts.

The source is well documented and the implementation is decently readable -- much easier than an STL implementation.

Caveats

Array and Vector indices are 0-based, not 1-based.
Raw memory allocators are used, not the LuaJIT __new/__gc system, so you can only store simple data. In other words, if your cdata allocates memory or other resources, you will need to manage that manually.
Right now the hash function is identity (hash(x) = x), so keys are limited to simple numeric types and pointers.
Although raw memory allocators are used, they may allocate memory in the range which LuaJIT desires. The impact of this depends on which allocator you use and your OS.

TODO

ldoc in wiki
TODOs in HashMap

Support

Submit feature requests and bug reports at the Issues page on GitHub.

Contributors

Evan Wies

Acknowledgments

Many thanks to Professor Pat Morin for a well written textbook and readable implementations, both released with open licenses. HashMap is based on his ChainedHashTable. Read and learn at opendatastructures.org.

LICENSE

lds is distributed under the MIT License.

lds - LuaJIT Data Structures

Copyright (c) 2012-2020 Evan Wies. All rights reserved

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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