Introduction

• Ashwin Hirschi
• • contact: ashwin@reflexis.com
• Reflexis B.V.
• • company founded 1999
  • software development & consultancy
  • small-to-medium-to-large-sized customers
  • actively using Lua since 2002

Purpose of this talk

Problem? What problem?

Problem? What problem? (2)

• How are you going to deploy your "solution"?
• » Users won't accept a cmdline tool with some scripts
• » Web-based solutions are not always desirable
• How do you create a friendly user experience?
• Will you write a new host app for each solution?
• Does every user's desktop need an install?
• How will you distribute updates?

Reflexis Lite Features

• compact, Lua-driven, Windows platform
• many useful libraries
• open-ended GUI system
• convenient multi-threading
• integrated profiler
• practical deployment

Libraries

• sockets (luasocket)
• database (xtx/xdb or sqlite)
• XML (pieces)
• regex (pcre)
• buffering
• compression (zlib/zip)

Graphical User Interface

• soft/scripted message handling
• renders using GDI, "cycle-based" object collection
• open DIY widgets ("areas") approach
• double-buffered, for flicker-free rendering
• some highlights: auto-sizing elements, virtual (and hybrid!) listboxes, adaptive font selection & sizing, schemes
• typical implementation sizes: statusbar <2k, button 5k, (multi-)text 7k, navbar 9k, listview 16k

Graphical User Interface (2)

• "actions" ease mapping of handlers to events
• form definitions based on Lua syntax
• table-based, automatic layouting
• consistent support for: context-menus, tab order, help requests
• booklets (GUI applets) orchestrate front-end handling
• the "scratchpad" booklet acts as console for vanilla Lua scripts

Graphical User Interface (3)

• limitations (by design!): only 1 window, no menu bar
• implementation shortcuts: edit boxes, menus, file dialogs
• missing pieces: handling of viewports, bitmaps, multi-level menus

Multi-threading: Boxes

• a Lua state
• two threads: controller + worker
• a thread-safe message queue
• a name (used as ID)

Multi-threading: Boxes (2)

• Boxes are created and destroyed from the main state only:
• » openbox, loadbox, execbox, closebox, hasbox
• But anyone can send messages to boxes:
• » sendbox
• Messaging is a-synchronous (mostly)

Multi-threading: Boxes (3)

• controller vs worker threads:
• » master – slave, i.e. controller starts worker
• » high – low priority, i.e. controller can/will interrupt worker
• workers can help dealing with "blocking" situations
• threads are suspended/resumed (not created/destroyed)
• dual-threading is optional

Deployment

• typical install = 1 executable + 1 application file (= EXE + ARK)
• the executable is small: typically 200-250 Kb (UPX-compressed)
• auto-configuring: runs from anywhere
• libraries are statically linked
• no external dependencies
• supports Win95 through WinXP
• runs comfortably on old hardware

Deployment (2)

• library scripts, e.g. UI system, DB utilities, Internet protocols
• application scripts
• application "booklets" (GUI-specific logic)
• GUI data, like form definitions, colour schemes
• other application-specific data
• boot script (optional license key file etc.)

Profiler

• fully integrated (i.e. embedded in runtime)
• uses high-frequency performance counters for accurate timings
• a single "profiler" function allows full control:
• » on, off, fetch, state, reset
• can be activated on-demand, e.g. for specific code sections
• timing results can be extracted using callback

Changes

• a home-grown "require" implementation
• » can also support "alternatives", like zip-or-db based setups
• a "compile" primitive
• » based on luac code, to drive in-house tooling etc.
• John Belmonte's weak references patch
• » mainly used for publish-subscribe system
• Fixes & adjustments to LuaSocket

Advantages

• fast, incremental development cycles
• same tooling for initial prototype and final product
• systems are easy to develop/debug/fix (alerts)
• products can evolve, don't build what you don't need (right now)
• new developers are always quickly up to speed

Advantages (2)

• same language across different configurations:
• » clients & servers, desktop & web, products & tools, etc.
• » code re-use saves time and increases quality
• extremely light-weight tooling:
• » no need for high-end dev machines
• » no licensing fuss, etc.
• » overall... much cheaper!

Advantages (3)

• extremely stable runtime, in production use for 4 years
• very responsive UI, also on low-end machines
• much richer user experience than browsers
• easy installs: simply copy to machine or run off shared drive
• updates consist of single files (ARKs)

Disadvantages

• Lua 4 - Lua 5(.1) breakage
• » table traversal changes break 80% of code base (Yay? NOT!)

Lessons learned

• It pays off to implement as much as possible in Lua:
• » more forgiving & flexible, so easier to evolve/extend/tweak
• » much faster to develop, so more time to focus on product!

 
• We succeeded because we created a Lua-driven platform!

 
• Last but not least, Lua is seriously high quality software!

The End?