Re: [9fans] Re: advantages of limbo

[David Presotto <presotto@closedmind.org>]

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.  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.

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.

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