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Structured concurrency and Lua (part 1)

John Belmonte, 2022-Sep

I've started writing a toy structured concurrency implementation for the Lua programming language. Some motivations:

use it as a simple introduction to structured concurrency from the perspective of Lua (this article)
learn the fundamental properties of structured concurrency and how to implement them
share code that could become the starting point for a real Lua library and framework

So what is structured concurrency? For now, I'll just say that it's a programming paradigm that makes managing concurrency (arguably the hardest problem of computer science) an order of magnitude easier in many contexts. It achieves this in ways that seem subtle to us—clearly so, since its utility didn't reach critical mass until around 2018[^sc_birth] (just as control structures like functions, if, and while weren't introduced to languages until long after the first compu

WSL install another distro

Here are some default vars for the process

ISO_DIR=~/fedora;
ROOTFS_MOUNT_DIR=/mnt/contents

DISTRO_LOCATION=

(This is a translation of the original article in Japanese by moratorium08.)

(UPDATE (22/3/2019): Added some corrections provided by the original author.)

Writing your own OS to run on a handmade CPU is a pretty ambitious project, but I've managed to get it working pretty well so I'm going to write some notes about how I did it.

Scaling your API with rate limiters

The following are examples of the four types rate limiters discussed in the accompanying blog post. In the examples below I've used pseudocode-like Ruby, so if you're unfamiliar with Ruby you should be able to easily translate this approach to other languages. Complete examples in Ruby are also provided later in this gist.

In most cases you'll want all these examples to be classes, but I've used simple functions here to keep the code samples brief.

Request rate limiter

This uses a basic token bucket algorithm and relies on the fact that Redis scripts execute atomically. No other operations can run between fetching the count and writing the new count.

	FROM hayd/alpine-deno:1.10.1
	WORKDIR /src/app

	ADD deps.ts ./
	RUN ["deno", "cache", "deps.ts"]

	ADD *.ts ./
	RUN ["deno", "cache", "mod.ts"]

	ENTRYPOINT ["deno", "run", "--unstable", "--allow-net", "--allow-hrtime", "--allow-env", "--cached-only", "--no-check", "mod.ts"]

	require "sqlite3"
	require 'set'
	require 'byebug'
	# Will be rebuilt at any time. Nice and incremental.
	db = SQLite3::Database.new "index.db"

	# Keep prefix indexes for "mos*" searches.
	#
	# TODO: It doesn't seem like SQLITE FTS5 supports synonyms well. That's ok, but
	# we're going to want that. We can download this database from Princeton, write

	FROM buildpack-deps:stretch-scm

	# gcc for cgo
	RUN apt-get update && apt-get install -y --no-install-recommends \
	g++ \
	gcc \
	libc6-dev \
	make \
	pkg-config \
	&& rm -rf /var/lib/apt/lists/*

	/*
	MIT License
	Copyright (c) 2018 Jonas Balsfulland
	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

	[Unit]
	Description=standalone kubelet
	After=docker.service
	Requires=docker.service

	[Service]
	User=root
	ExecStartPre=-/bin/docker kill kubby
	ExecStartPre=-/bin/docker rm kubby
	ExecStartPre=-/bin/docker create \

	# LVDB - LLOOGG Memory DB
	# Copyriht (C) 2009 Salvatore Sanfilippo <[email protected]>
	# All Rights Reserved

	# TODO
	# - cron with cleanup of timedout clients, automatic dump
	# - the dump should use array startsearch to write it line by line
	# and may just use gets to read element by element and load the whole state.
	# - 'help','stopserver','saveandstopserver','save','load','reset','keys' commands.
	# - ttl with milliseconds resolution 'ttl a 1000'. Check ttl in dump!