From: "Iñaki Baz Castillo" <ibc@...>
Date: 2012-05-16T16:49:57+09:00
Subject: Re: How to ensure that a block runs entirely after other threads? (Thread.exclusive does not "work")

2012/5/16 Robert Klemme <shortcutter@googlemail.com>:
> That's a perfectly appropriate way to handle that: you don't want to
> incur synchronization overhead for all users even if they do not need
> access from multiple threads.  Even worse, there are cases where only
> the user can decide which synchronization is appropriate.  For example
> the infamous cache idiom
>
> if cache.include? x
>  y = cache.get(x)
> else
>  y = create_y(x)
>  cache.put(x, y)
> end
>
> (I know, which Hash there are more elegant solutions - this is for
> illustration purposes only.)
>
> In this case you cannot guarantee consistency by internally
> synchronizing all methods of "cache" if it must be avoided that two
> threads invoke create_y() for the same x.


100% agreed.

Thanks a lot.

-- 
Iñaki Baz Castillo
<ibc@aliax.net>