concurrentlua

Is this a good time to mention concurrentlua, a reimplementation of Erlang's concurrency model in Lua, using coroutines to model processes? https://github.com/lefcha/concurrentlua It has not seen a lot development over the past ... couple of years, but it worked quite nicely when I last tried it.

Yes, that must have been the one I was thinking of! :) I was very happy a couple of years back when I was building a toy project in C and Lua to come across a Lua library called concurrentlua[1] that implemented Erlang-style message passing (without pattern matching, though, IIRC). It even allowed you to send messages across machines. [1] https://github.com/lefcha/concurrentlua

Concurrency in Lua's core language is co-operative (coroutines explicitly yield to each other). This is because the language designers don't want to impose any particular threading architecture -- Lua is intentded to be as portable and non-opinionated about that sort of thing as possible. Its coroutines are intended for the same sort of issues as generators/callbacks/continuations, not for explicit parallelism. They won't do multi-core mapreduce, but they'll let you cleanly factor code that has multiple main loops. You can get multi-threaded/multi-process concurrency by messaging between separate Lua VMs, using libraries such as Lua Lanes (http://kotisivu.dnainternet.net/askok/bin/lanes/). The Lua VM is implemented without static state, so several VMs can run in the same process without a GIL. There is LuaPi (https://github.com/LuaDist/lu