From: Ara.T.Howard@...
Date: 2004-09-11T02:35:01+09:00
Subject: Re: Variable scoping

On Sat, 11 Sep 2004, Brian Candler wrote:

>> This is because you have never read ruby-man-1.4, and it's very bad :-)
>
> You mean very bad of me not to read it? Fair enough. I _have_ read quite a
> lot though :-) Besides, we can all make mistakes.

well - not guy really ;-)

> | while TRUE
> |   ns = gs.accept
> |   print(ns, " is accepted\n")
> |   Thread.start do
> |     s = ns			# save to dynamic variable
>
> But isn't there a race there? That is, if the interpreter context-switches
> after the Thread.start, goes back around the loop, and ns is assigned to a
> new object before "s = ns" is executed.
>
> I think for safety you should do
>
>  Thread.start(ns) do |s|
>
> But that's the trouble with this thread-safety stuff. Maybe 999 out of 1000
> times the previous code would work. It's almost certainly not possible to
> catch that sort of problem with unit-testing, unless you splatter "sleep"s
> all over the code when testing.
>
> Some sort of static indication of a possible problem would be very useful.
>
> It would have to be able to tell that:
>  - you are using a variable within a Thread .... block
>  - the variable may be assigned to again by the other thread
>    (which, in this case, is an *earlier* assignment because it's in a loop)
>
> Regards,
>
> Brian.

why not fork?  it's not that expensive anymore and would solve most of your
problems.

-a
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