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- Subject: Re: multiple interpreters x multiple threads x multiple environments
- From: Mark@... (Mark Ian Barlow)
- Date: Mon, 22 Sep 1997 15:53:51 GMT
In message <199709091844.PAA08845@server02> email@example.com writes:
> About the on-going discussion on multiple threads:
Well, it *was* ongoing; sorry, I had to do a bit of paying work.
> Like Roberto said, multiple threads of execution in Lua would require
> support on the C part, something that neither ANSI C nor POSIX can give.
Am I right or wrong in thinking that the ANSI C definition of setjmp() and
longjmp() permits home-cooked co-routines? I can certainly do it in Turbo C,
which I have always found to be pretty strict in adhering to the standard.
Basically, I chop up the available stack by recursing down it, planting
a setjmp() at my chosen intervals and filling in an array of jmp_bufs as I
go. I can then longjmp() to any one I choose from my scheduling kernel, but
of course there's no protection to prevent me exceeding my self-imposed
stack size in each co-routine, so recursion within individual co-routines
whould require some caution. Am I exploiting a feature that pure ANSI C does
not necessarily support? Here's a simple function that chops the stack
into equal chunks...
extern void reschedule(const int thread_tag);
void prepare_stacks( const int n_stacks,
const int stack_depth,
const int depth_count,
jmp_buf *jbuf_array )
/* N.B: Units of 'stack_depth' are sizeof(this function's stack frame) */
stack_depth, /* continue recursing and */
depth_count - 1, /* decrement frame count */
const int stacks_remaining = n_stacks - 1;
int thread_tag = setjmp(jbuf_array[stacks_remaining]);
reschedule(thread_tag); /* scheduler called our longjmp() */
else if (stacks_remaining)
stack_depth, /* head down again but */
stack_depth, /* reset frame count */
<snip stuff about multiple interpreters>
> Multiple environments are easy to implement in Lua.
> One way is as Roberto mentioned: use tables to save and restore the global
> Another way is to use the setglobal/getglobal tag methods.
> In this solution, these tag methods are used to filter and redirect requests
> to read and write the global environment, say to tables.
> To switch environments, simply change the handlers for setglobal/getglobal.
This (latter) method takes care of a fast environment switch; If I
restricted myself to, say, switching context only at specific time-
slice de-scheduling points, maybe even only at function entry/exit
(via the debugger interface) how much else would I need to save?
-- Mark Ian Barlow Non-Linear Control Consultants Ltd.
Mark@nlcc.demon.co.uk Voice / Fax: +44 (0)1207 562 154