RE: Tricky c#/LuaInterface Question

Hi

Thanks for the reply. I went with a simple solution of using a mutex, so that when I was executing in the Lua code I take the mutex and then when the script calls sleep and exits back out into the C# sleep function I release the mutex so that event handlers are safe to call into the Lua core again to execute a Lua callback function.

I have tested this pretty heavily it seems solid now. I have had 4 fast timers created and running from a Lua script without a crash.

As a follow up question, I was maybe hoping in the future I could expand on what I have now to spin up two Windows threads from C# and then execute two entirely separate Lua contexts (both use LuaInterface of course)

I was thinking this should be threadsafe as the start of the task does something like this.

lua = new Lua();
lua.RegisterFunction("printToApp", this, GetType().GetMethod("printToApp"));

This idea seems to be flawed though from a quick experiment I did. Having two threads each create a new Lua instance and register a few simple functions always crashes on execution.

Does anyone have some insight into is it possible to run 2 totally independent threads with LuaInterface ? Any help would be appreciated. Thanks

Geoff

Date: Tue, 18 Nov 2014 12:32:34 +0100
From: marco@mastropaolo.com
To: lua-l@lists.lua.org
Subject: Re: Tricky c#/LuaInterface Question

Sorry for the typos and missing links.. I'm on mobile.

There are several solutions :

1. Use another time class. .NET has a ton of timers most of which dispatch on a single thread in a non reentrant way. They are less precise but easier to work with.

2. Set the synchronization object of the timer to some UI element for automatic dispatching.

3. Use a Dispatcher or a SynchronizationContext to dispatch execution on the thread you want.

4. Set AutoReset to false - this should suffice to work (you have to manually restart the timer though). I would consider using a lock to handle concurrency in a safe way, though.

Note that as far as I know, Lua and LuaInterface will not complain if you use it from different threads as long as it's only one thread at the time.

I might be wrong though.

Shameless plug: you can also check other interface layers for C# and Lua like NLua, SharpLua, MoonSharp, UniLua, and KopiLua. As I'm the author of one of these I listed them in random order but all are good ;) None will help you much in this scenario but should be easier to handle on other aspects.

Il 18/nov/2014 11:25 "Geoff Smith" <spammealot1@live.co.uk> ha scritto:

Hello

I have been using LuaInterface for a little while, I have got on pretty well with it so far until I hit this difficult problem. The documentation for it doesn't really help me much on this issue, so hopefully someone here might be able to assist please.

I wanted to add a feature where I can create timers on the Lua side with something like

timerRefNum = myAPI.createTimer(1000, myCallbackHandler) -- 1 sec timer

then at the bottom of my Lua script I might have something like

while true do
myApi.sleep(100) -- Lua sleeps for 100 mS while nothing much to do
end

I am not the most experienced C# coders, but the outline for this code on the C# side seemed fairly easy.

I create a System.Timers.Timer for each Lua createTimer() call and add a c# ElapsedEvent handler which then calls the associated Lua function.

After having written the C# code I ran a Lua test script with 2 separate timers firing at 500 mS and 1000 mS intervals, with 2 different Lua handlers. This appeared to work fine and ran for 15 minutes or so before crashing. :(

Of course my solution is fatally flawed, what I overlooked was that the main Lua thread will be executing in Windows thread "x", then timer 1 fires and that C# handler will run in thread "'y", the second timer fires and that runs in thread "z"

As Lua / LuaInterface isn't threadsafe that is what I believe is causing the crash. I am struggling now to see how I would implement this timer functionality properly and threadsafe.

Any ideas or links to similar example code snippets would be much appreciated. Thanks

Regards Geoff