Re: [TCLCORE] VWAIT documentation

[<lm...@bi...>]

I'm not a strong voice here but Twylite's request seems pretty reasonable,
just including an example that shows the prob in the docs would be better.
At my company we have a goal: "drive towards zero support costs".  This
request seems in line with that.  If tweaking the docs means less people
ask questions, why not?

On Thu, May 07, 2009 at 09:37:52AM +0200, Twylite wrote:
> Hi,
> >> As such, we will like to request that the following statement
> >> extracted from wiki.tcl.tk/1302 by Chris Nelson to be included in the
> >> standard documentation:
> >>     
> >>    Multiple VWAITS NEST, THEY DO NOT HAPPEN IN PARALLEL. THE
> >> OUTERMOST VWAIT CANNOT COMPLETE UNTIL ALL OTHERS RETURN.
> >>     
> > The standard documentation appears clear on this matter to me.
> > The entire second paragraph of the DESCRIPTION section is
> > devoted to discussing it.
> This has historically been a source of problems for new Tcl users, and I 
> am inclined to feel (now that I have re-read it) that the 8.5 man page 
> for vwait is a little too narrative and does not succinctly explain the 
> behaviour of nested vwaits as the above proposal does. 
> 
> In fact it (the man page) fails completely to explain that unrelated 
> vwaits can cause blocking.  For example:
>   after 500 { vwait b; puts "b was set" }
>   after 1000 { set a 10 }
>   vwait a
>   puts "Never get here"
> 
> This example has nothing to do with "the event handler that sets varName 
> ... not complete[ing] immediately" as described in the man page, but 
> rather that the unrelated "vwait b" creates a new event loop which 
> blocks "vwait a" until the "vwait b" returns.
> 
> On this basis I support the proposal to have the above statement (or 
> something similar) included in the man page.
> 
> Regards,
> Twylite
> 
> 
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-- 
---
Larry McVoy                lm at bitmover.com           http://www.bitkeeper.com