From: Csaba Henk <csaba@..._for_avoiding_spam.org>
Date: 2005-02-27T19:54:58+09:00
Subject: Re: assignments and thread safety

On 2005-02-27, nobu.nokada@softhome.net <nobu.nokada@softhome.net> wrote:
> Hi,
>
> At Sun, 27 Feb 2005 17:43:47 +0900,
> Yohanes Santoso wrote in [ruby-talk:132474]:
>> > Is "$a ||= 1" thread safe? I'd guess so, as "||=" is one piece of
>> 
>> It is not guaranteed to be thread-safe, although in current official
>> ruby vm it is 'atomic'.
>
> It is impossilbe.
>
> What do you expect for:
>
>   $a ||= very.long.operation?

Well, I had there "$a ||= 1", and fetching 1 is not a
very.long.operation. 

But I see the point... even if concretely with 1 being the assinged
value, "$a ||= 1" happens atomically (which could be the case for other
literals and variables on the right hand side), it's necessarily
accidental, so to say. "||=" can't have the value of the right hand side
at its invocation...

Csaba