Re: Calling functions in other states

[David Olofson <david@...>]

On Thursday 15 November 2007, Tom Miles wrote:
> I apologise if this is either a stupid question, or has been asked
> before, but I was wondering if there was a way that I haven't found
> of calling functions of one state from within a lua script of
> another?

Well, my first thought is "you don't." No matter how you implement it, 
you're going to end up with a caller->callie->caller roundtrip, and 
no matter how you implement it, there is going to be some latency and 
overhead. It's a simple way of dealing with multithreading, but it's 
inherently very inefficient in most applications.


> I have several states all started with lua_newthread() all  
> of which run their own scripts.  I have a very convoluted method at
> the moment for each thread to "talk to each other" which is
> hideously slow and has been a nightmare to maintain as new
> situations arise, and was wondering what the "industry standard" way
> of doing it was (if there was one)?

For an effective and (relatively speaking) simple solution, try some 
form of message passing. Basically the same low level functionality 
as RPC (Remote Procedure Calls), but you just send a message and get 
on with your work, without waiting for a response. The receiver will 
eventually process the message and, if appropriate, send back a 
response message.

You can implement RPC over a system like this, but RPC is a 
fundamentally broken design unless you really don't have anything 
useful to do while waiting for the "return".


//David Olofson - Programmer, Composer, Open Source Advocate

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