Re: [9fans] Re: advantages of limbo

[David Tolpin <dvd@davidashen.net>]

> From 9fans-admin@cse.psu.edu  Tue Mar  2 12:02:21 2004
> Subject: Re: [9fans] Re: advantages of limbo
> From: David Presotto <presotto@closedmind.org>
> To: 9fans@cse.psu.edu
> Content-Type: text/plain; charset="US-ASCII"
> Date: Tue, 2 Mar 2004 03:02:46 -0500
>
> On the topic of garbage collectors, one of the main reasons for reference
> counting objects and immediately releasing them when they become unreachable
> was to use garbage collection to allow control not only of memory but also
> resources memory represents.  The typical example given is one of windows
> that go away as soon as the last reference to them (actually the object representing
> them) goes away.  

Does that mean that designers of Inferno windowing system were
required to avoid using cyclic references in window structures?
That is, a window does not know who its creator is? 

It's a decision. But a limiting one. Influenced by an implementation.
Just running garbage collector with limited scope would do it
without limitations.

> Also, the reference counting had a distinct advantage of
> being fixed time.  We had a terrible time with java systems of the time
> going away for long periods, both because of the garbage collector going
> off and because of the odd interactions in finalize routines in various
> classes.

It was not a tradeoff of normal garbage collection. Fixed-time garbage
collection techniques existed long before java. It was just an early
implementation to make it running.

> Over the years since limbo appeared, java garbage collection has changed
> radicly and often, drasticly reducing the 'time to take a coffee break'
> garbage collection runs.  By the 1.4.1 jdk, java included 6 or more
> gabage collection strategies and all sorts of tuning parameters.  Along
> the way all sorts of user code was written to avoid tickling the collectors
> at the wrong time or to get things done before they went off.   That's
> a hell of a lot of effort to avoid the small differences advertised by
> the proponents of m&s and generational gc over reference counting.

Among 61864 lines of tight Java code I have been involved in writing
during last two years there is not a single line which was written to
avoid tickling the collector at the wrong time. It just works.

> Of course, limbo isn't immune from odd timings.  However, they do require
> reference loops and those seem not very common amongst limbo programmers.
>

Is there any other reason reference loops are not very common amongs
limbo programmers besides limitations of the garbage collector?

David